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AbstractThis research report describes a 10-year long monitoring project about recent

weathering and erosion on Bronze Age rock carvings in southern and central Sweden. Main objectives are to describe the micro topography of a selection of rock carvings accurately, to calculate recent downwearing rates and also to deduce the spatial variability of deterioration and how it varies in time. The investigations have been made with a flat bed laser scanner especially constructed for the purpose. The scanner records the micro topography of rock surfaces with a height resolution of 0.025 mm, within a measurement range of 100 mm. The maximum area that can be scanned is about 40x40 mm and usually one height recording is taken for each square mm. The scanner is described in chapter 3, together with a critical review of its possibilities.

A total of 43 sites have been laser scanned, and repeated measurements were made at 26 of these sites. The investigated places have been chosen together with experts on rock cravings within the different study areas. From the field data, among others, accurate contour maps, 3-D images and digital shadow images can be made. It is also possible to treat the data statistically in various ways. Calculations of surface roughness have, for example, proved to be useful when describing and comparing different sites with each other. From the places where repeated measurements have been made recent downwearing rates have been computed. This has been done by subtraction of consecutive field data grids from each other. How all calculations are made and how to interpret the results is described in chapter 4.

In chapter 5 there is a systematic description of all investigated sites, with measurement results and opinions about the present weathering status and possible future risks for continuing deterioration. Several different minor weathering phenomena are associated with the downwearing on the investigated areas. These are described in chapter 6. In chapter 7 there is an attempt to classify the status of all laser scanned sites on a scale from 1 to 6.

There are large variations in downwearing rates between the investigated places. At a few places they can be considered as disastrous. At most sites recent deterioration is detected, but average rates are, however, similar to or lower than those that can be expected for crystalline rocks in general in Scandinavia (1-2 mm in 1000 years). It has also been revealed that the micro weathering is episodic. This means that periods with fast breakdown alternate with periods when almost nothing happens. There is also a pronounced spatial variation of where downwearing happens. Usually deterioration at times only takes place on limited spots while most of the micro mapped area is left unaffected. After material losses have taken place from these spots weathering continues at other places. The research is, together with several other types of studies, of value when taking decisions about future management of valuable rock carving areas. Especially it makes our understanding about how micro weathering proceeds in Scandinavian crystalline rocks better than before.

Key words: rock carvings, downwearing rates, micro weathering, laser scanning, southern and central Sweden, rock surface roughness, micro maps

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Contents

Abstract 1

Contents 2

1. Introduction 5

2. Weathering and its causes 7

3. Methods for field measurements 9

3.1. Direct measurement methods 9

3.2. The laser scanner 10

3.2.1. Principle of the laser scanner device 11

3.2.2. The laser gauge probe 11

3.2.3. Signal processing and control of measurements 12

3.2.4. Restraints of triangulation lasers 14

3.3. Field procedures 15

4. Methods for processing the data 17

4.1. Roughness calculations 17

4.1.1. The calculation method 17

4.1.2. Examples of other numerical methods 18

4.1.3. What does roughness data tell? 18

4.2. Calculation of material losses 19

4.2.1. Comparison of consecutive micro maps 19

4.2.2. How to interpret the calculation of material losses 20

5. Site descriptions 22

5.1. Blekinge län 22

5.1.1. Torhamn 11 (Hästhällen, Möckleryd), Nr 1 22

5.2. Kalmar län 28

5.2.1. Gamleby 54, Nr 2 28

5.2.2. Lofta 353 (Vittinge), Nr 3 29

5.3. Skåne län 31

5.3.1. Gryt 1 (Frännarp), Nr 4 31

5.3.2. Järrestad 13 (Dansarenhällen), Nr 5 32

5.3.3. Simrishamn 23, a 34

5.4. Stockholms län 36

5.4.1. Ösmo 622, Nr 6 36

5.4.2. Turinge 441, b 37

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5.5. Södermanlands län 38

5.5.1. Nicolai församling 340 (Släbro), Nr 7 & c 38

5.6. Uppsala län 40

5.6.1. Boglösa 138 (Rickeby), Nr 8 & d 40

5.6.2. Litslena 194 (Ullstämma), Nr 9 42

5.6.3. Vårfrukyrka 192 (cup marks), Nr 10 43

5.6.4. Boglösa 141, e 45

5.7. Västra Götalands län, province of Bohuslän 45

5.7.1. Brastad 141 (man with big hand), Nr 11 46

5.7.2. Brastad 18 (deer figure), Nr 12 48

5.7.3. Foss 6 (Lökeberg), Nr 13 48

5.7.4. Skee 614 (Massleberg), g 50

5.7.5. Skee 619 (Jörlov), Nr 15 50

5.7.6. Tanum 12 (Aspeberget), Nr 16, h & i 52

5.7.7. Tanum 18 (Aspeberget, ship), j 56

5.7.8. Tanum 26 (Aspeberget, horse), k 57

5.7.9. Tanum 255 (Fossum), Nr 17 58

5.7.10.Tanum 72 (Tegneby, Mellangården), l 60

5.7.11.Tanum 417 (Kalleby, Västergården), m 60

5.8. Västra Götalands län, province of Dalsland 61

5.8.1. Tisselskog 11 (Högsbyn, the meadow), Nr 18 61

5.8.2. Tisselskog 15 (Högsbyn, Ronarudden), Nr 19 62

5.8.3. Tisselskog 12 (Högsbyn, foot-sole), n 64

5.9. Västra Götaland län, province of Västergötland 64

5.9.1. Husaby 70 (Flyhov), Nr 14 & f 64

5.10. Östergötlands län 68

5.10.1.Borg 51 (Herrebro), Nr 20 69

5.10.2.St. Johannes 14 (Egna hem), Nr 21 70

5.10.3.Västra Tollstad 21 (Hästholmen), Nr 22 72

5.10.4.Östra Eneby 1 (Himmelstalund), Nr 23 & o 72

5.10.5.Östra Eneby 8 (Fiskeby), Nr 24 & p 74

5.10.6.Östra Eneby 23 (Ekenberg), q 76

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6. Weathering phenomena at the investigated sites 77

6.1. Visible signs of deterioration 77

6.1.1. Surface coloration 77

6.1.2. Mineral weathering and pitting 79

6.1.3. Flaking 79

6.1.4. Gneiss weathering 80

6.1.5. Widened joints 81

6.1.6. Angular rock fragments 81

6.1.7. Granular disintegration 82

6.1.8. Karren forms 83

6.2. Reasons for breakdown at the investigated sites 83

7. Status of the investigated rock carving sites 85

8. General discussion and conclusions 88

8.1. Discussion 88

8.2. Main conclusions 90

References 92

Appendix 96

Table of material balance calculations 96

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Chapter 1. Introduction The main objective of this research report is to describe the micro topography and to

show results from calculations of downwearing rates at a selection of rock carving sites in southern and central Sweden. For these purposes a laser scanner with a fully computerised data collection system has been constructed. During the project time the scanner has continuously been modernised to make it easier to carry and to facilitate the use of it in the field. How the equipment works and how measurements taken with it should be interpreted is described in chapter 3 and 4. A total number of 43 sites have been investigated. At 26 of these places repeated measurements, during a monitoring period reaching from 1994 to 2003, have been made in order to follow the course of recent deterioration. The sites have been chosen in order to represent different rock types and environments. It is also an aim that they should represent the main rock carving areas within southern and central Sweden. The choice of objects to investigate has been done together with staff from the Swedish board of antiquities as well as with regional and local authorities.

The method, together with some initial measurements of rock carvings, is presented by Swantesson (1992c) and likewise by Swantesson & Oldberg (1993). The outlines of the project described in this research report and early results are accounted for by Swantesson (1996a). Early results are also found in Swantesson (1996b). The laser scanning method has also proved to be of great use for other purposes. It has, for example, been possible to read runic inscriptions that were difficult to interpret with conventional methods (Hagland, 1998, Swantesson, 1998 and Swantesson & Gustavson, 2005). Laser scanning has furthermore been made within the frame of an EU-project at twenty coastal sections in five European countries. At each section five sites were monitored between 1999 and 2001 in order to calculate weathering and erosion rates in environments influenced by marine processes (Swantesson, 2006a).

This research report deals only with the actual investigations and conclusions that can be drawn from the achieved results. For those having a more general interest in Bronze Age rock carvings in Sweden there is, however, a wealth of literature available. It is only possible to mention a tiny fraction of it here. Unfortunately the bulk of the written material is in Swedish. One such book that can serve as an introduction to the main rock carving areas in Sweden, also for the international reader, is written by Hasselrot (1984). It contains many high quality artistic photographs of the Bronze Age stone art. The book by Janson et al. (1989) gives a more extensive review of the most important areas. Experts on the rock carvings in the respective provinces described wrote the different chapters. It also contains English summaries. In a book by Hygen & Bengtsson (2000) the focus is on the UNESCO world cultural heritage area in the province of Bohuslän and on the neighbouring province of Østfold in Norway.

Examples of publications where the rock carving areas are treated more scientifically in English are Bertilsson (1987) and Coles (2000). The first author deals with the northern part of the province of Bohuslän and the second author describes areas in the southwestern part of the province of Uppland. Intense recent research involving a wide variety of scientific disciplines has been made in the borderland area between Sweden and Norway in the provinces of Bohuslän and of Østfold. Some of the results are published, but much is

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yet to appear. Kallhovd & Magnusson (2000) give an extensive overview of the investigations that are currently being made in this area.

The Swedish board of antiquities has initially funded the research presented in this report. During the last two years financial support has come from the RANE-project, 1BSR, Interreg 3B. The investigations have also benefited from the EU-project ESPED (European Shore Platform Erosion Dynamics), MAS3-CT98.0173. The same laser scanner as for the micro mappings of the rock carvings was used in this project about rock deterioration at the coast. Resources were made available for modernisation of the scanner device and comparisons with other areas, measured in an identical way, were made possible. During the long time span of the monitoring project contacts with numerous people have taken place. There have been many valuable and interesting interchanges of opinions. My main discussion partner during the entire research period has been Runo Löfvendahl at the Swedish board of antiquities, who always has been interested in the progress of the investigations. Gunnar Berg constructed the electronics belonging to the laser scanner device and Magnus Jansson wrote the main part of the software needed for the data acquisition and control of the laser scanning process.

Despite that discussions have taken place with authorities, several scientists in many disciplines and other experts all conclusions and opinions in this research report must be regarded as the author’s own.

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Chapter 2. Weathering and its causes Weathering can be defined as ‘processes at are near the earth surface in order to bring

minerals and rocks into equilibrium with present environmental conditions’. In this context it must be realised that almost all rock material we see around us initially is formed at totally different temperatures and pressures than those we experience in the biosphere, where we live, today. Weathering usually makes the rock ‘softer’ which can lead to that material losses happens from rock surfaces. The actual detachment or erosion can take place in several ways. Agencies behind it can except the weathering itself, for example, be running water, slope processes, coastal waves, glacial ice or the wind. Weathering and erosion contribute together to the actual downwearing or denudation that is observed in nature. The processes are occurring naturally but man might sometimes influence rates. It is difficult to assess how great the impact of, for example, pollution, acidification and other anthropogenic factors are upon the speed of natural downwearing.

It is generally agreed that weathering processes can be divided into three distinct groups (Ollier, 1984 and Bland & Rolls, 1998). The first is by chemical reactions, the second by physical (mechanical) action and the third by biological activity. The biological or biotic weathering, however, works either chemically or physically. It is beyond the scope of this research report to give an extensive account about the weathering processes and their complicated nature. Only a brief summary of some main aspects is given here. The reader who is interested in the topic is referred to student textbooks such as Ollier (1984) and Bland & Rolls (1998) for a more complete introduction.

Chemical weathering involves solution and alterations by which new minerals are formed. One process is that ions are released by solution and are removed with the water that drains the actual area. Among common rock types this predominantly occurs in limestones. The process when water molecules are incorporated into the lattice of a mineral is called hydration. The most well known example is when anhydrite associates with water and forms gypsum. Hydrolysis is different from hydration since it involves a real chemical reaction between water and a mineral. When, for example, potassium feldspar reacts with water one of the new minerals that can be formed is the clay mineral kaolinite. The new minerals created by hydrolysis are more stable than the initial ones. Another common chemical weathering process is reduction and oxidation reactions. Ferrous iron (Fe2+) is, for example, frequently oxidised into ferric iron (Fe3+) in nature. By this reaction easily observed rusty and reddish colours are created. Complexes are compounds in which molecules or ions form co-ordinate bonds to a metal atom or ion. The formation of complexes is important for the release and mobilisation of iron(III) (Fe3+) and aluminium(III) (Al3+) especially in soil profiles. Generally chemical weathering goes faster in warm climates since reaction rates increase with temperature.

In contrary to chemical weathering no compositional changes are involved in physical or mechanical weathering. There is only disintegration into smaller components. As its chemical counterpart mechanical breakdown can take place by many various processes. The concept of freeze-thaw weathering is fairly well known. Usually it is described as water that freezes into ice increase in volume and exerts pressure on the surrounding rock, causing failure. This is an oversimplification and there are several, more or less

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complicated, ways by which freezing water can disintegrate the rock. Salts are effective mechanical weathering agents. They can exert strong pressures when they crystallise from a solution or when their crystalline form is hydrated. Wetting alternating with drying can cause disintegration especially in softer rocks or in rocks that already have experienced other types of weathering. Insolation by the sun during the day increases the temperature of rock surfaces and is accompanied by a slight volume increase. It is often meant that this, if it is repeated enough many times, can lead to rupture. The effect of solar heating is probably limited. Abrupt temperature changes caused by fires and by lightning are, however, highly effective for rock breakdown. Pressure release is another process that ought to be mentioned in this context. Other rocks might previously have overlain the rocks that we see today in nature. These rocks have been eroded away and the response to the release of the burden is the formation of sheet joints. The burden might also have been the land ice.

Many different organisms are important for biological weathering. Bacteria can, for example, influence downwearing rates by the release of carbon dioxide, by being engaged in the nitrification process and by the oxidation of metals. Lichens and also fungi work biophysically by the penetration of hyphae into existing micro-cracks, and by the expansion of thalli and hyphae due to water absorption. The main biochemical action of lichens is the emission of organic acids which can be very effective in causing mineral alteration. Algae can also fracture rocks and in addition they are able to participate in the dislocation and precipitation of metals at rock surfaces. It is often said that plant roots growing in existing fractures exerts a pressure on the rock that is sufficient for rupture. This is probably only possible in very week rocks. The main contribution to weathering by plant rotes is instead both emission and absorption of varying substances as a part of their life processes. They form a very complex biochemical micro system. Furthermore is decaying plant and animal matter an important factor in biotic weathering. Large amounts of carbon dioxide are produced as well as humic and fulvic acid.

In nature several of the above mentioned weathering processes work together to bring about rock deterioration. It is almost never possible to point out a single process as the main responsible factor for the actual weathering at a certain place. Chemical alteration might, for example, weaken the rock and it can also lead to volume changes. This will facilitate the work for mechanical and biomechanical agents. The disintegration by mechanical action will in its turn increase the area of attack for chemical reactions and produce a larger number of cracks where, for example, lichen hyphae can penetrate.

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Chapter 3. Methods for field measurements Weathering and rock breakdown in Scandinavian crystalline rocks is generally very

slow. Of this reason it has not until recently, with the introduction of modern advanced technique, been possible to perform direct measurements of downwearing rates. Indirect methods to estimate rock denudation rates during the Holocene have been used by, for example, Dahl (1967) and Rudberg (1970). They measured the height of quartz veins and nodules protruding above the rest of the rock. This assumes that the land ice left a smoothly polished surface and that the quartz only has weathered to a very limited extent during the Holocene. They arrived at minimum downwearing rates between 1.05 and 1.5 mm in 1000 years. Later André (1996) presents deterioration rates between 0.1 and 1.3 mm in 1000 years in quartzite, quartz phyllite and amphibolite from the Abisko area in northern Sweden.

3.1. Direct measurement methods The most commonly used technique, especially in Anglo-Saxon countries, for direct

measurements of rock downwearing is the MEM (micro erosion meter). It is a mechanical instrument that is low in weight and easily can be handled in the field. High & Hanna (1970) describe the standard version of the device in detail. The main component of the MEM is an engineer’s dial gauge mounted on a triangular base plate. Heights are recorded manually by lowering the probe of the dial gauge gently onto the rock surface. For repeated recordings three studs with hemispherical heads have to be permanently attached to the rock. When measurements are made the legs of the MEM rests on these studs. The bases of the legs are differently shaped. The first leg has a conical depression, the second a V-notch while the third leg is flat. This makes replacements of the MEM on the studs easy and very exact. Since the dial gauge is mounted slightly off centre three recordings can be made at each site by rotating the device on the studs. Provided a good calibration procedure is used readings can be said to be correct within 0.05 mm (Spate et al., 1985).

Several improvements of the MEM have been made and Trudgill et al. (1981) describes a traversing instrument allowing up to 1000 readings to be made. The use of this type of devices is, however, very time consuming. Generally a large number of MEM sites have to be installed to be able to calculate accurate mean downwearing rates since there usually is a considerable spatial variation of rock breakdown over short distances. Where weathering is slow an even larger amount of sites is needed to obtain reliable results. The number of recordings that can be achieved by any MEM is far to low in the investigated areas in southern and south central Sweden. In softer rocks the method has, however, been successful to monitor building stone decay in polluted urban environments (Trudgill et al., 2001). Comparisons between the MEM and the same laser scanner that has been used in the project reported here are found in articles by Williams et al., (2000) and Swantesson et al., (2006a). Advantages and disadvantages of the respective methods are treated.

Photogrammetric methods fulfil the requirements of giving a 3-dimensional image of an area of chosen size. Repeated measurements can be made and the downwearing of rock surfaces calculated. For good results the costs of the apparatus needed are relatively high

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and great skill of the operator is essential. An overview of photogrammetric methods for the study of rock surfaces is made by Inkpen et al. (2000).

3.2. The laser scanner A prototype of the flat bed laser scanner used for micro mapping of the rock carvings is

together with early results already described by Swantesson (1989). At this stage the device had several limitations, of which its weight of about 150 kg was the most disadvantageous. Most of the equipment was during field measurements housed in a van and micro mappings could not be made further away from a road than 30 m, restricted by the length of the cables connecting the laser scanner with electronics and a computer. A further disadvantage was that an alternating current generator driven by petrol served as power source. Handling of it was difficult and it also made significant noise. Since the investigations started the equipment has been gradually improved and the total weight of all components is now below 30 kg. Two persons can easily carry the device several 100 m, and it is transportable in an ordinary car.

Figure 1. Sketch of the principal construction of the laser scanner device. A = laser light source and

detector. B = stepping motors. C = laser probe processing unit. D = two 12 V batteries. E = portable

computer. F = box with cards for controlling the measurement process and the data processing. From

Williams et al. (2000).

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3.2.1. Principle of the laser scanner device

The principal construction of the laser scanner equipment of flat bed type is seen in figure 1. The central unit of the scanner is a commercially available laser gauge probe of the triangulation type. The probe is moved in the x- and y-directions by means of two stepping motors and timing belts. The motors are mounted on a specially designed aluminium frame with four adjustable legs. Three of the legs have the same types of bases as on a MEM, while the fourth leg serves as a support and prevents the frame from tilting. This allows the fast and reliable repositioning of the instrument with studs secured to the rock. This relocation system has, however, not been used when measuring the Bronze Age rock carvings as described below in section 3.3. Software for controlling the measurement process and for data collection as well as control cards have been especially developed for the purpose. The cards are housed in a separate box. Upon the box is, while measuring, a portable computer placed that serves as the main control unit. The device uses 24 V at an amperage of 1.5 A. In the field two rechargeable 12 V batteries of motor cycle type, each weighing 4 kg, are used as power source. Cables connect the different units of the equipment. By unscrewing the cables from their contacts the device can be carried and transported in parts. The power of the motors is sufficient to move the probe accurately for measurements of surfaces of all inclinations. For vertical or steeply inclined areas the frame has, however, to be secured by, for example straps to prevent it from moving when measurements are taken.

3.2.2. The laser gauge probe

The principle of the triangulation laser gauge probe that has been used in the project is seen in figure 2. The low power SELCOM® GeAs laser emits IR light with a wavelength of 850 nm. Where the laser beam hits the rock surface a red spot with a diameter of about 0.2 mm can easily be seen with the aid of an IR-viewer. The operator can thus detect which part of the rock that currently is measured. On newer versions of the laser scanner device, used in other projects (Williams et al., 2000 & Swantesson et al., 2006a), visible red light with a wavelength of 670 nm is used instead. Via the detector of the laser gauge probe heights can be recorded with a resolution of 0.025 mm within a measurement range of 100 mm (figure 2). Since some noise can occur the resulting accuracy is approximately 0.1 mm. Before final treatment of collected data they are pre-processed in the laser probe processing unit attached to the frame.

Laser gauge probes with a better resolution are available. However, if the resolution, for example, is five times as good the measurement range will generally decrease with the same amount. A measurement range of 100 mm allows for most height differences within the scanned areas of maximally about 40x40 cm. The laser scanner developed for this project can be used under all external light conditions. Even bright sunlight does not affect the reliability of recorded data. Neither does the colour of the measured surface influence the quality of the collected values. Highly transparent minerals and water on the rock surface, however, makes that something else than the true surface is measured.

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Figure 2. The principle of an optical triangulation laser gauge probe. The laser light is focused through a

lens and hits the rock surface at A. The reflected light from A is focused through another lens at point A’on a detector. If the light beam instead hits the rock surface at B, the reflection will be focused at B’.The distance between A’ and B’ is a measure of the height difference between A and B. In the sketch

this is the maximum that can be recorded with the laser probe used in the project. The angle between

the laser beam and the optical axis of the detector is 18˚. From Williams et al. (2000).

3.2.3. Signal processing and control of measurements

The signal-processing card, housed in a separate box together with other control cards, receives serial data from the laser unit. According to the operator’s choice an average of 32, 64, 128 or 256 height values is calculated and transformed to parallel data by a processor. It is necessary to calculate an average since the single values emitted from the laser can be disturbed and are not enough accurate. The laser used in the project has a frequency of 16 kHz and the speed of the stepping motor has been set to 25 mm per second in the x-direction. For almost all measurements a mean was calculated for 128 original heights.

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This value was sent to the computer, via a PCMCIA card, and represents an average of heights over a distance of 0.2 mm. The two cards controlling the motors are autonomous and communicate with the computer serially.

The entire measurement process and the data acquisition are controlled in the field from a portable computer. Originally all software was made for the MS-DOS environment. Later this was transformed to fit the Windows environment, which made the software easier to use for the operator. Real time communication is established with the signal-processing card, since problems arise because the processor of the computer sometimes is blocked by the Windows operating system. This part of the software is written in C while menus are written in Visual Basic. The laser probe can from the menu be demanded to move to any desired point within the frame area with minimum increments of 0.1 mm in the x- and y-directions. The height value of this point is displayed and this function is used when the positions of reference studs are recorded. Tests of repeated measurements of such studs, mainly by unskilled volunteers, indicate that their positions can be determined with a standard deviation of ±0.25 mm in the x- and y-directions (Williams et al., 2000).

From the menu the size of the area to be scanned can be chosen up to the maximum possible of 380x420 mm. Furthermore the spacing between averaged height values to be saved on the computer can be selected. The minimum possible distance is 0.4 mm. For the measurements of the Bronze Age rock carvings the distance has in almost all cases been 1 mm in both the x- and the y-direction. When these settings have been made the machine can for control by the operator be demanded to move along the borders of the chosen measurement square. It can also be ordered to start the measurement process. When a micro mapping begins the laser gauge probe is first always moved by the program to the origo position x, z = 0, 0. After this initiation the laser moves to the chosen starting point and the measurement process commences. Height values are collected when the x-motor moves the laser probe at constant speed. Then the laser probe is moved back, but no values are saved to the computer. The reason is that there is a slight backlash in the axis of the motor that can cause inaccuracy. Measurements are thus only made during movements in one direction. After this procedure the other motor moves the probe one increment in the y-direction and the process will be automatically repeated until the entire area has been scanned.

No further effort is needed from the operator until the laser scan is finished. The progress of the measurement process can, however, be followed on the display of the computer. Furthermore a display on the box containing the control cards shows approximately where the measured rock surface lies within the measurement range of the laser gauge probe or if it accidentally lies without it. The recorded height value data is saved to the computer as a sequential file, with a header that makes it directly available for further treatment with the commercially available software SURFER®. Since distances in the x- and y-directions are known an x, y, z-file can as well easily be created. Among other things that can be mentioned about the possibilities of the menu, on the computer screen, is that the special software controlling advanced settings of the motor control cards is accessible from it.

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3.2.4. Restraints of triangulation lasers

Apart from the restraint caused by the accuracy of the instrument and the possible measurement range the time needed for a complete scan can sometimes produce problems. A micro mapping of the maximum possible area of about 40x40 cm with a spacing of 1 mm between recorded heights in the x- and y-directions takes about 2 hours to perform. For most of the reported measurements this means that the scanning time has exceeded 1½ hour. The time for positioning the device is not included. The weather thus has to be stable when fieldwork is conducted since rain and water on the rock surface cause incorrect results. Much faster measurements can now be done, but such technique was not available when the project with assessing the breakdown of Bronze Age rock carvings started.

Figure 3. Blindspots and secondary reflections that can arise when a triangulation laser is used (not to

scale). A: No reflection can reach the detector because the step in the rock surface is steeper than 72°.

B: No reflection can reach the detector from beneath the miniature overhang. C: Secondary reflections

can create erroneous readings. From Williams et al. (2000).

There are, however, some restraints that not can be easily overcome with any type of triangulation laser. This is illustrated in figure 3. Since there is an angle between the optical axis of the laser beam and the detector of the gauge probe steep steps in the rock surface

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becomes invisible for the detector. For the used laser probe the angle between the two axes is 18°, meaning that inclinations of more than 72° not will be detected. When the scanner traverses such areas a red warning light appears on the control box and the last correct value is repeated in the recorded data file until the area with invalid height values has been passed. That no point beneath miniature overhangs, as seen in figure 3 B, can be detected is more obvious. Secondary reflections can arise near steep parts of the rock surface. This problem is partly due to the properties of the surface that is measured. These restraints means that the best micro maps are achieved on fairly smooth rock surfaces without to many abrupt height variations.

3.3. Field procedures When a single micro mapping shall be made the field procedure is relatively simple.

The different parts of the device are assembled and the frame is placed on the object to be measured. Best results are achieved when the x, y-plane of the frame is roughly parallel to the rock surface. Caution has to be taken that the area to be scanned lies within the measurement range of the laser gauge probe. On vertical or highly inclined surfaces the frame has to be securely tightened. The complete equipment during field measurements is seen in figure 4.

When repeated measurements are planned on one site, for assessing downwearing rates, the measurement procedure is somewhat more complicated. To be able to replace the laser scanner frame on the site some kind of fix points are needed. The type of relatively large studs used when taking measurements with a MEM are fairly reliable for exact replacements. With the laser scanner frame that is much larger also this system can cause minor inaccuracies, since significant temperature variations between measurements might alter the size of the frame slightly. Much more important is, however, that large permanent studs not can be placed in the immediate vicinity of sensitive Bronze Age rock carvings of ethical reasons.

Instead four small studs especially designed for the project have been attached to the rock surface at each place where repeated micro mappings were made. The studs are of stainless steel and are usually placed within already damaged parts near the rock carvings. A hole with a diameter of 3.5 mm and a depth of about 10 mm is drilled into the rock. The hole is filled with epoxy glue and the stud is placed into the hole and becomes securely fastened to the rock. The heads of the studs are flat with a diameter of 6 mm and they are placed level with the rock surface. Unless it is known where to find the studs they are not easily detected and they thus only disturbs the environment to a very limited degree. There is a minor depression in the middle of the head of each stud. The exact position of this point is carefully recorded, with the laser scanner, in connection with every measurement at the site. Unlike the larger MEM studs it is not possible to place the legs of the frame directly upon them. Neither is it possible to position the laser frame identically for all measurements. Instead the recordings of the x-, y- and z-values of the four fix points is a requirement that makes recalculations between scanner data taken at consecutive occasions possible. When such recalculations have been made overlays and comparisons between

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different micro maps are possible. At a few sites naturally occurring protruding parts of harder mineral have been used instead of the studs. This has, however, been less exact.

Figure 4. The complete laser scanner device during measurement at a rock carving site in Gamleby in

the county of Kalmar. All parts of the equipment described in the principal sketch in figure 1 are seen on

the photograph. The IR-viewer necessary to see where the laser beam hits the rock surface lies

between the control box and the laser scanner frame.

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Chapter 4. Methods for processing the dataSince all measurement data is stored in a computer directly in the field as a sequential

file it is immediately available for visualisations and further calculations. Contour maps, 3-D images and digital shadow images of the scanned area are, for example, readily made. A digital shadow image resembles a photograph, but is constructed only with the aid of the recorded height values. It has the advantage that there is no disturbance from different colours and shades of grey when, for example, chiselled details are viewed. For this type of work the software SURFER® has proved to meet most demands. Examples of these types of images are found in chapter 5, where all measured sites are described. Furthermore all height values of the resulting grids can be observed. The regular grid data also makes all kinds of statistical computations possible.

4.1. Roughness calculations The calculation of surface roughness indexes is an effective and objective method for a

numerical presentation of the micro topography of rock surfaces. This makes in many cases comparisons between different areas easier than from images alone since the information is found in a condensed form. As seen in tables 3, 4, 5 & 6 in chapter 5 there are significant differences in the surface roughness between the investigated areas. The surface roughness is always referred to in the descriptions of the different sites. The calculations presented in this report have been made according to a method described by Swantesson (1992a).

4.1.1. The calculation method

For the roughness calculations the laser-scanned surfaces have been divided in squares, each comprising 100 evenly spaced height values. This has been done both for squares measuring 10x10 mm, with a spacing of 1 mm between heights used in the computations, and for squares measuring 20x20 mm, with a spacing of 2 mm. In both cases the best fit of a sloping plane has first been calculated. The roughness index has then been expressed as the standard deviation ( ) of height values in mm from this plane multiplied by 100.

Usually surface roughness indexes are computed from 144 squares at each scanned area, which makes further statistical treatment of the data possible. In a few cases when slightly smaller areas were micro mapped indexes from 100 squares were obtained. For the squares measuring 10x10 mm the roughness calculations of the 144 indexes were made from the lower left part of the laser scanned area. The distribution of roughness values can, for example, be plotted in histograms and the mean and the median value at each site can be determined. Examples of such histograms, with a class width of 2.5, are found in chapter 5 where the sites are described.

Furthermore the standard deviation, the skew and the kurtosis of the distribution is calculated. The results are presented in tables in chapter 5. The skew is expressed as

(xi-xmean)3p(x)/ 3. This is a measure of the asymmetry of a distribution. A positive value means that there is a longer tail to the right, while a negative value means that there is a longer tail to the left. The kurtosis is expressed as ((xi-xmean)4p(x)/ 4)-3, and describes

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how sharp the peak of a distribution is. The value is 0 for a perfect normal distribution, above 0 if it is peaked and below 0 if it is flat.

4.1.2. Examples of other numerical methods

There are several other possible statistical methods that can be applied on the recorded data that will gain information about the scanned rock surfaces. It is not possible to give a complete account here. Roughness calculations can, for example, also be done from line scans instead of area scans. Such methods are described by among others McCarroll (1992) and McCarroll & Nesje (1996). Obviously an area scan contains a large number of lines that can be used in this context. Both methods have been used for a number of coastal sites in Mallorca. The two types of calculations give fairly similar results.

A fractal approach is also possible. Fractals have been used to describe natural irregular and fragmented structures such as relief, coastlines and rivers (Mandelbrot, 1983 and Turcotte, 1993). The fractal analysis can also be applied on micro topography and a regular grid of laser scanned heights is a good data source. It can, for example, be determined if certain objects or structures are true fractals, with one single fractal dimension. If they instead are pseudo fractals, with several distinct fractal dimensions, their discontinuity and/or inflection points can also be determined (Cachão, 1995). This can serve as an important descriptive and interpretative tool about which geomorphologic processes that have acted upon the investigated surface. Comparisons between fractal analysis and roughness calculations from the same sites show that results are fairly difficult to correlate. The two methods thus describe different properties of the rock surface and can be considered to be complementary to each other.

4.1.3. What does roughness data tell?

Provided that rock types with similar mineralogy and grain sizes are compared roughness data gives an excellent measure of how far weathering has reached (Swantesson, 1992a). In Scandinavia it can usually be assumed that most rock surfaces were fairly smoothly polished after the land ice left the area, and that the only micro relief was due to fine glacial striations. When weathering starts it often acts differently on different minerals and thus slowly produces a somewhat more pronounced micro relief. Initially there is a gradual increase in the surface roughness with time. Further breakdown will later only give slightly higher mean and median values of roughness, but the skew of the roughness index distribution tends to become more positive. This is due to a larger number of more abrupt small steps on the rock surface with a longer time of exposure. The majority of the roughness values are usually grouped fairly well together but some considerably higher values give the positive skew. The abrupt steps create a larger number of such higher values. With few exceptions the kurtosis shows that the distribution is peaked compared to a perfect normal distribution. This is also an indication that the majority of the roughness values usually are grouped together on each site.

When the tables in chapter 5 are read it is also seen that the standard deviation ( ) of roughness indexes is highly variable between the different sites. A low standard deviation means that the rock surface have similar characteristics over the entire scanned area, while

- 19 -

a higher value means that there are variations between smooth parts and parts with a more pronounced micro relief. The 1:st and 3:rd quartile values of the roughness indexes are also numbers that helps in understanding the micro topography variations of the scanned surfaces. It must, however, not be forgotten that surface roughness to a great extent is a rock property. Roughness data gives a description of rock surfaces but they can not be used for absolute dating. When interpreting the status of rock carvings the data, however, often gives clues about for how long time the investigated sites have been exposed to weathering. It is, for example, likely that a smooth and well-preserved surface has been covered for a long time between the Bronze Age and the present.

4.2. Calculation of material losses When making measurements in the field you will inevitably encounter certain problems

that never occur during controlled laboratory conditions. These problems always cause a certain inaccuracy of the resulting micro maps. They are usually not serious when only a single laser scan is made at a field site. When two consecutive measurements are compared more serious difficulties can, however, arise since the disturbances are not the same at both occasions. One factor inducing errors is that the lichen cover on the rock outcrop has varied from time to time. Ideally measurements should only have been performed on areas where lichens were absent. This was not possible due to the character of the investigated objects. Before measurements the area to be scanned was cleaned with water and a soft brush. With this method it was not always possible to remove the lichen cover completely. During measurements it could be observed that leaves, needles and dust were blowing across the measurement square. They could accidentally be recorded by the detector and cause a false height value. Another problem that has occurred at some places is that ants walk across the scanned area. They will cause false height readings when hit by the laser beam.

4.2.1. Comparison of consecutive micro maps

Naturally images from two consecutive laser scans of the same site can be placed next to each other and details can then be compared manually. This is, however, very time consuming and a quantitative measure of material losses can never be achieved. If the laser scanner really is in exactly the same position during both measurement occasions the grid from the first scan can simply be subtracted from the second one, giving a resulting grid indicating where and to what extent material losses have occurred. Since it was not possible to relocate the laser scanner frame exactly for each measurement, one of the two grids has to be recalculated to make this subtraction possible. For this purpose a so-called affine transformation, using the recorded x-, y- and z-values of the four small fix points, was applied. This type of transformation allows rotation, translation and scale changes, while parallelism, projective properties and topology always are preserved (Hauska & Harrie, 1999). Unfortunately such recalculations introduce certain extra inaccuracies that have to be added to those that are due to the field measurements themselves.

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4.2.2. How to interpret the calculations of material losses

All results from the calculations are found in the table in the appendix, and the results are referred to in chapter 5 ‘Site descriptions’. cut-fill is the result from the simple subtraction of the two grid files and is stated in mm3. A negative value means material loss, while a positive value indicates a volume increase. denud. (denudation) is a measure of the average surface level lowering (negative value) or rise (positive value) in mm that has occurred between the two indicated measurements. Both these figures are very crude and can usually not be used for any interpretations of downwearing rates. It is, from sites where no changes have taken place, estimated that the maximum possible error of the denudation calculation can be as high as ±0.25 mm.

Despite the affine transformation small variations in the placing of the laser scanner frame between micro mappings can cause fairly large errors in the calculations. For example, if the inclination of the frame has varied slightly between measurements parallax errors can arise. In this case not exactly the same point on the rock surface will be recorded although the x- and y-position given by the frame position is the same. These errors are negligible at heights that are in the same z-plane as the four fix points, but increase with growing distance from the plane. Another reason why the errors are fairly large is that one height recording is taken for each square mm, but only within a small part of it. A minor change in the positioning of the laser scanner thus also causes another point of the rock surface to be measured. All errors are largest on sites with many small steep rock steps and/or joints where also false reflections and missing values due to the triangulation laser technique are substantial. The resulting errors can partly be overcome by using a denser grid during the scans. This was not possible with the laser scanner used but can fairly easily be achieved with more modern equipment. Most important is, however, to solve the relocation problem of the device better when similar measurements are performed. Another reason for some of the errors is that the manual recordings of the x- and y-positions of the fix points sometimes not have been accurate enough.

For the calculations of downwearing rates only material losses that have taken place beneath depths of 0.5 mm are considered. Despite the problems described above we can with few exceptions be sure that a real removal of rock fragments has occurred in these cases. After the subtraction of the first laser scan file from the second a smoothing of the resulting material balance grid file is made. The aim of the smoothing is to reduce noise, such as single erroneous height values that still can be present especially at joints or other abrupt edges. The calculations of material losses in mm3 to depths of more than 0.5 mm and the area affected by rock removal to depths deeper than this in mm2 are done on the smoothed grid. The downwearing rate is calculated as surface lowering in mm in 1000 years and is based on the material losses to depths of more than 0.5 mm.

The resulting figures are excellent for a reliable comparison of the different investigated sites. Images with contour maps of the resulting smoothed grids give a very good picture of the spatial variation of downwearing within the scanned areas and to what extent rock removal has taken place. Examples of such images are found in chapter 5, ‘Site descriptions’. It must, however, be remembered that the indicated downwearing rates are conservative measures and should be interpreted as minimum values of deterioration. At sites with a high natural downwearing rate there is a relatively small difference between the

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calculated and the real one. At other places with a slower downwearing the real rate can in worst cases be estimated to be twice as fast as the calculated (Swantesson, 2005). This is the case for most of the investigated rock carving sites. The table in the appendix should always be read together with the descriptions of the sites in chapter 5. The reliability of the calculated results is described in connection with each site. It is also accounted for how micro topographical and environmental factors can have affected the accuracy of the calculated results.

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Chapter 5. Site descriptions All investigated sites are described in this chapter. They are accounted for county by

county in alphabetical order. The places where repeated measurements have taken place are listed in table 1, and their positions are seen on the map in figure 5. The co-ordinates in ‘Rikets Nät’ (RT90) in the table are either taken from the economical map at the scale 1:10000 or with a simple handheld GPS. In both cases the accuracy can be estimated to be about 10 m. Furthermore the number of micro mappings at each site is stated in the table, as well as the calculated surface lowering in mm per 1000 years. Sites where only one micro mapping has been made are listed in table 2.

Statistics from the roughness calculations are reproduced in table 3 & 4 for those places where multiple measurements have been made, and in table 5 & 6 for places where only one measurement has been made. The values shown in table 3 & 5 are based on calculations from squares sized 10x10 mm. Those in table 4 & 6 are calculated from squares sized 20x20 mm. How the computations are made and how to interpret the results is described in detail in chapter 4, ‘Methods for processing the data’, on page 17.

5.1. Blekinge län In the county of Blekinge only one site has been measured. It is situated in the parish of

Torhamn at Möckleryd in the SE part of Blekinge. The prevailing bedrock in the area consists of acid, intermediate intrusive rocks. They are usually gneissic and the schistosity is generally dense.

5.1.1. Torhamn 11 (Hästhällen, Möckleryd), Nr 1

The investigated outcrop of a few 100 square m forms an open area within a pine forest. It is fairly flat and slight inclinations in all aspects occur. Lichens are abundant, especially where damaged parts exist. The carvings consist among others of about 50 ships. The first impression is that the rock generally is in a good state. Large parts seem to be original surfaces with micro glacial striations, almost entirely in the feldspar. There are, however, substantial areas that display shallow damage. It is difficult to conclude whether those areas result from anthropogenic influence or from natural weathering. One characteristic feature of the rock carvings on the outcrop is that they are made very shallow. The red paint used to facilitate the study of the carvings for the public is in most cases even in height with the surrounding rock. The shallowness of the figures probably indicates that the rock was almost perfectly glacially polished when they were made.

Micro mappings were performed over an area consisting of a few ships, with adjacent deteriorated parts, at three occasions. The first measurement took place in August 1995, the second in August 1998 and the third in June 2002. Calculations show a minimum downwearing rate of 0.47 mm per 1000 years during the period between 1998 and 2002 and a rate of 0.65 mm per 1000 years for the entire period between 1995 and 2002. As seen in figure 6 the breakdown has occurred at seven major spots, all of which are situated at the edge between more or less original surfaces and already damaged parts. It can also be concluded that the downwearing was slightly faster between the first and second

- 23 -

measurement than between the second and third. However, fragments continued to get lost from several places. When the roughness is viewed in table 3 & 4 it can be seen that the calculated values are near the average for all measured rock carving sites. The reason that the apparently smooth outcrop does not show lower values is that the sharp contrast between original feldspar areas and parts where grains have been removed is depicted. The skewness and kurtosis are relatively low since there are few abrupt edges and that the contact to damaged parts usually is slightly concave.

Figure 5. Outline map showing the location of rock carving sites where micro-mappings have been

made at more than one occasion during the period 1994-2003. The numbers correspond to those in

table 1. The co-ordinates in the margins are in ‘Rikets Nät’ (RT90).

1300000 1400000 1500000 1600000

6200000

6300000

6400000

6500000

6600000

1.

2.3.

4.

5.

6.

7.

8. 10.9.

11.12. 13.

14.

15.

16. 17.

18.

19.

20. 21.

22.

24. 23.

- 24 -

Table 1. Sites where micro-mappings have been performed at multiple occasions. The numbers

correspond to those on the map in figure 5. The co-ordinates are in ‘Rikets Nät’ (RT90). A is the number

of measurements made during the period 1994-2003. B is the range of calculated surface lowering at

different time intervals at the micro-mapped sites in mm per 1000 years. The sign – means that the

results are inconclusive. The reader is referred to the main text for information about how the

calculations were made and how to interpret the results.

County and site Coordinates A B

Blekinge län

1. Torhamn 11 (Hästhällen, Möckleryd) 6221100 1501862 3 0.47 – 0.65

Kalmar län

2. Gamleby 54 (in built up area) 6418530 1535812 3 0.18 – 0.20

3. Lofta 353 (Vittinge) 6421881 1540902 2 0.04

Skåne län

4. Gryt 1 (Frännarp) 6231869 1389954 3 0.21 – 0.42

5. Järrestad 13 (Dansarenhällen) 6158922 1403672 3 -

Stockholms län

6. Ösmo 622 (Nynäshamn municipality) 6541334 1621073 3 -

Södermanlands län

7. Nicolai 340 (Släbro, Nyköping) 6517188 1567884 4 0.04 – 0.28

Uppsala län

8. Boglösa 138 (Rickeby) 6610512 1574973 7 0.00 – 0.71

9. Litslena 194 (Ullstämma) 6614622 1581991 3 0.10 – 1.11

10. Vårfrukyrka 192 (cup marks) 6611055 1574702 3 -

Västra Götalands län

11. Brastad 141 (man with hand) 6479730 1246535 4 0.00

12. Brastad 18 (deer figure) 6482980 1247639 3 0.01 – 0.10

13. Foss 6 (Lökeberg) 6484633 1255103 3 3.73

14. Husaby 70 (Flyhov) 6492705 1359761 5 2.46 – 60.83

15. Skee 619 (Jörlov) 6547485 1242406 4 1.79 – 2.13

16. Tanum 12 (Aspeberget) 6516714 1241168 5 < 0.01 – 1.12

17. Tanum 255 (Fossum) 6519778 1243970 4 0.01 – 0.03

18. Tisselskog 11 (Högsbyn, the meadow) 6535219 1302579 4 0.13 – 1.56

19. Tisselskog 15 (Högsbyn, Ronarudden) 6534901 1302510 3 < 0.01 – 0.30

Östergötlands län

20. Borg 51 (Herrebro) 6494978 1517245 3 0.00 – 0.93

21. St. Johannes 14 (Egna hem) 6494667 1522848 3 0.22 – 0.25

22. Västra Tollstad 21 (Hästholmen) 6461952 1431510 3 0.00 – 0.07

23. Östra Eneby 1 (Himmelstalund) 6496841 1519663 5 0.06 – 0.21

24. Östra Eneby 8 (Fiskeby) 6497029 1518221 4 0.01

- 25 -

Table 3. Statistics from surface roughness calculations at rock carving sites where measurements have

taken place at more than one occasion. The calculations are based on 100 evenly distributed height

values in squares sized 10x10 mm.

Site Min Max Mean Median 1:st qu 3:rd qu skew kurt

Torhamn 11 13.19 48.77 27.21 26.81 22.89 30.58 6.20 0.81 1.28

Gamleby 54 16.64 41.62 24.56 22.96 21.34 27.59 5.27 1.10 1.08

Lofta 353 8.31 71.29 16.96 14.16 12.44 17.96 9.47 3.47 14.44

Gryt 1 8.02 40.43 24.27 24.58 20.10 28.45 6.03 -0.07 -0.12

Järrestad 13 13.36 144.59 29.76 21.88 18.57 30.27 20.26 2.56 8.46

Ösmo 622 18.03 140.45 42.84 39.38 31.38 49.45 17.55 2.30 8.39

Nicolai 340 13.75 141.84 28.57 22.38 19.00 27.56 19.55 3.37 12.99

Boglösa 138 13.60 113.46 33.52 27.95 22.40 37.53 18.00 2.06 4.56

Litslena 194 11.03 126.59 28.32 22.95 18.32 31.34 16.80 2.81 10.27

Vårfrukyrka 192 16.62 73.24 34.28 31.71 26.23 40.24 10.92 1.01 0.83

Brastad 141 18.21 58.08 28.36 27.42 24.39 31.08 5.99 1.48 4.12

Brastad 18 18.95 100.61 35.68 31.19 27.84 38.19 13.50 1.97 4.53

Foss 6 17.41 131.50 37.89 34.23 26.43 43.82 16.42 2.47 10.24

Husaby 70 6.82 51.09 18.29 16.08 13.09 21.75 8.13 1.41 2.14

Skee 619 20.41 67.24 36.09 35.05 30.15 41.58 8.25 0.88 1.53

Tanum 12 (I) 16.62 49.96 33.68 33.97 29.94 38.64 7.07 -0.25 0.02

Tanum 12 (II) 20.89 44.89 30.29 30.17 26.54 33.63 4.93 0.46 0.16

Tanum 12 (III) 22.70 53.89 33.56 33.01 29.32 37.46 5.81 0.74 1.09

Tanum 255 15.89 50.15 31.05 30.96 26.86 35.80 7.08 0.05 -0.23

Tisselskog 11 7.82 106.83 31.10 27.58 16.55 39.45 19.22 1.80 4.27

Tisselskog 15 4.26 319.02 43.65 30.53 17.89 51.84 43.23 3.39 15.43

Borg 51 11.47 122.08 26.37 23.46 19.67 28.16 13.15 3.73 20.64

St. Johannes 14 11.00 77.72 29.90 26.44 20.43 35.88 12.99 1.34 2.14

Västra Tollstad 21 11.20 39.24 18.70 17.92 15.57 21.44 4.64 1.47 3.89

Östra Eneby 1 10.19 110.36 26.68 23.47 19.08 30.31 12.41 3.11 15.26

Östra Eneby 8 7.14 67.88 18.26 16.54 12.90 21.48 7.60 2.36 11.72

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Table 4. Statistics from surface roughness calculations at rock carving sites where measurements have

taken place at more than one occasion. The calculations are based on 100 evenly distributed height

values in squares sized 20x20 mm.

Site Min Max Mean Median 1:st qu 3:rd qu skew kurt

Torhamn 11 18.21 74.88 34.75 32.13 27.06 40.80 10.54 1.35 2.03

Gamleby 54 18.99 90.73 35.03 31.45 26.44 39.76 12.95 2.64 5.10

Lofta 353 12.64 152.33 38.01 32.24 21.10 45.32 23.37 1.93 4.73

Gryt 1 23.12 68.39 38.59 37.74 31.23 44.01 9.02 0.65 0.14

Järrestad 13 13.44 237.41 39.30 27.64 21.46 38.90 36.92 3.53 13.88

Ösmo 622 23.56 206.47 64.24 61.16 45.71 77.07 24.76 1.72 6.72

Nicolai 340 19.73 165.94 42.68 35.50 28.82 43.25 23.81 2.54 7.43

Boglösa 138 22.43 159.96 44.38 38.82 31.90 47.29 22.11 2.95 10.73

Litslena 194 18.39 129.78 47.45 40.42 30.65 57.03 23.60 1.36 1.53

Vårfrukyrka 192 25.12 143.96 71.68 65.61 46.23 91.83 30.74 0.70 -0.43

Brastad 141 17.50 65.41 31.66 29.12 24.95 36.51 9.35 1.18 1.65

Brastad 18 26.63 139.49 45.96 41.04 36.01 48.69 17.78 2.68 8.86

Foss 6 21.75 194.30 74.14 69.58 48.08 91.07 33.49 0.97 0.72

Husaby 70 8.31 83.67 33.29 30.69 23.33 42.72 14.30 0.78 0.63

Skee 619 32.29 84.19 48.62 48.40 42.61 53.07 8.66 0.78 1.19

Tanum 12 (I) 23.03 63.51 41.71 42.07 36.24 46.99 8.46 0.02 -0.27

Tanum 12 (II) 23.80 57.99 37.99 37.45 33.81 41.77 5.95 0.43 0.46

Tanum 12 (III) 30.11 66.86 41.01 38.95 35.75 44.74 7.84 1.39 1.90

Tanum 255 22.42 61.81 36.19 35.98 30.95 40.77 7.09 0.48 0.50

Tisselskog 11 17.66 358.83 62.77 47.93 39.51 64.55 46.28 3.18 13.88

Tisselskog 15 18.37 209.95 70.69 63.36 39.50 82.03 45.25 1.53 1.92

Borg 51 19.87 94.75 41.75 38.52 32.00 50.10 13.68 1.01 0.91

St. Johannes 14 15.40 128.75 49.24 44.02 32.69 63.87 21.62 1.01 1.07

Västra Tollstad 21 18.21 41.59 26.82 26.30 23.29 29.79 4.92 0.18 0.73

Östra Eneby 1 16.82 98.46 40.13 36.29 30.00 46.68 14.34 1.21 1.74

Östra Eneby 8 10.92 92.16 37.66 34.26 26.07 47.31 16.65 1.03 0.95

- 27 -

The shape of the measured site is ideal for the equipment and such micro topographical features that makes recording with a triangulation laser less certain are not present. Of this reason it can undoubtedly be concluded that downwearing and destruction are active at present. Although the calculated rate is somewhat lower than what can be expected as an average for Swedish crystalline rocks there is a constant tearing of parts of the ship figures. The individual layers of the gneissic rock are fairly hard but due to the dense schistosity and weak support between the layers the rock carvings are susceptible to breakdown. The characteristics of the rock does not exclude that some of the present damaged areas were initiated already when the figures were cut. Furthermore people walking on the outcrop can cause wearing. The presence of pine needles on the rock might, due to their acidifying effect, as well influence the course of downwearing negatively.

Figure 6. Material losses to depths of more than 0.5 mm during the period 1995 to 2002 at Torhamn 11.

The contour interval is 0.25 mm. The largest damage in the bottom right corner of the image was mainly

produced between 1995 and 1998, while the cluster of lost fragments to the left in the image mainly

arose between 1998 and 2002.

100 150 200 250 300

mm

100

150

200

250

300

350

mm

- 28 -

5.2. Kalmar län Both measurement sites in Kalmar län lies in the vicinity of the town Västervik in the N

part of the county. Gamleby 54 is situated in a built-up area, while Lofta 353 lies on a small summit in a rural area. The bedrock in this area consists to a great extent of red to grey metasediments (Gavelin, 1984). The composition is highly variable, both considering mineralogy and chemistry. There is often a regular change between dark (grey) and light (pink) beds with thicknesses between 3 and 20 cm. The pink bands are rich in quartz and potassium feldspar, while biotite is the most common mineral in the grey bands. Orthoquartzites in connection with metasediments also occur.

5.2.1. Gamleby 54, Nr 2

The site in mainly dark metasediments lies near the centre of the village Gamleby. It is situated at the edge of the pavement of a small road, and a railroad as well as villas and lighter industries are present in the immediate vicinity. On the measured area there is one deeper, and a few smaller cup marks as well as the lower part of a ship. The average slope is 8º towards WNW. Damage due to flaking is numerous and several places where exfoliation sheets, of a thickness of less than 1 cm, have lost contact with the underlying rock, while still present, also exist. On more fresh parts of the rock glacial striations are obvious. Lichens are abundant and smaller lost rock fragments are found in minor joints and at lower parts.

Measurements were made in August 1995, in July 1997 and in June 2002. The total material loss is small and affects an area of 288 mm2 (figure 7). The calculated minimal deterioration rate is almost the same for both the entire period between 1995 and 2002 and for the period between 1997 and 2002. It varies between 0.18 and 0.20 mm per 1000 years. Between 1995 and 1997 a small hole, with a diameter of 8 mm, was created through a part of a flaking sheet where it had lost contact with the underlying rock and between 1997 and 2002 another exfoliated area was slightly extended. On other parts of the rock almost no changes are seen. The mean and median roughness values (table 3 & 4) are fairly low, while the minimum value is higher than at many other places. This describes the character of the parts of the measurement area having glacial striations. A few higher values are found at the edges of exfoliated parts and where cup marks exist. In the latter case it is most noticeable where the calculation is based on squares sized 20x20 cm.

Despite that the breakdown is fairly limited it is easily detected (figure 7), and it is seen that downwearing at this site mainly occurs by extension of exfoliated areas. Although the present deterioration rate is limited there is no reason to consider the state of the rock carvings as relatively safe. On parts of the measured area where the exfoliation sheets have lost contact with the underlying rock future breakdown can proceed very quickly. This is the case for several tenth of square cm. Already exfoliated areas on other parts of the measured site might also be extended fairly fast. The rock surfaces beneath the disappeared flaking sheets are temporarily stable. The alteration here is limited since this part has been protected from, for example, chemical alteration. This is, however, of little value since carvings as well have disappeared in those areas.

- 29 -

Figure 7. Material losses to depths of more than 0.5 mm during the period 1995 to 2002 at Gamleby 54.

The contour interval is 0.25 mm. The damage near the lower right corner is due to a hole through an

exfoliation sheet created between 1995 and 1997, while the largest spot in the upper part of the image

shows an extension of an exfoliated area that occurred between 1997 and 2002.

5.2.2. Lofta 353 (Vittinge), Nr 3

The locality lies on a roche moutonnée, forming a small summit, and is surrounded by farmland (figure 8). Glacial striations are visible at some places and there are limited numbers of quartz veins, which protrudes a few mm above the surrounding generally light metasediment. The measurement site is almost level, and consists in its upper part of a ship figure. Two obvious joints are crossing the figure. The contours of the ship are less clear near these joints than elsewhere. A damaged area, a few cm big, is present immediately beneath the rock carving. Triangular rock fragments, with sharp edges, are found at several places on the outcrop. These fragments that have been detached from the rock vary in size from about one mm up to some cm. The lichen cover seems to have increased considerably during the seven year long monitoring period.

50 100 150 200 250 300

mm

50

100

150

200

250

mm

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Measurements were made only twice, in August 1995 and in June 2002. Only a very limited material loss, corresponding to a denudation rate of 0.04 mm per 1000 years, was detected. It occurred at three minor spots along the joints. When calculations were made of the balance between cut and fill a fairly high positive value meaning a volume increase was received. This is, however, due to the fact that it was not possible to remove all lichens perfectly during the second micro mapping especially in the upper left part of the measurement quadrangle. The minimum roughness value, as well as the value for the 1: st quartile, is very low both in the statistics based on squares sized 10x10 mm and 20x20 mm. This describes the generally smooth surface of the metasediment. There are, however, several considerably higher values where the squares on which the calculations are based cross the joints.

Figure 8. The roche moutonnée surrounded by farmland on which the measurement site Lofta 353

(Vittinge) in the county of Kalmar is situated.

At present there are only limited changes at Lofta 353 (Vittinge) and most probably a dramatic increase in the downwearing rate will not take place in the near future. There is, however a risk that the joints crossing the ship figure will widen. The triangular rock fragments found on the outcrop also show that weathering is constantly going on in the immediate neighbourhood.

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5.3. Skåne län Micro mappings have been made at three places in the county of Skåne. The rock-

carving site at Frännarp in the parish of Gryt lies in the N part of the county. Reddish grey to greyish red granite that often is gneissic or porphyritic dominates in the area (Wikman et al., 1983). At the site the rock is usually coarse grained with phenocrysts. Joints are few and the predominating minerals are plagioclase, potassium feldspar and quartz. The potassium feldspar has sometimes suffered a sericite alteration. Biotite and hornblende are also present. Simrishamn and Järrestad lie in the SE part of Skåne. The bedrock here consists of Cambrian sandstone (Hardeberga sandstone). The pore space between the sand grains has been filled and the rock forms of this reason a massive and very hard quartzite (Wikman & Bergström, 1987).

5.3.1. Gryt 1 (Frännarp), Nr 4

Trees, mainly oak, shadow the entire site. This makes the environment fairly moist, and leaves and other organic material precipitates from the trees. Algae are present on the rock surfaces. In contrast to lichens they are, however, easily removable with water and a soft brush. The carving field slopes steeply, 25º towards WNW at the measurement site. The most common figures are carriages (figure 9), sometimes with horses in front of them. Glacial striations exist on parts of the outcrop and signs of glaciofluvial action in the form of plastic sculpture are present.

Measurements at the site were made at three occasions, in August 1995, August 1998 and in June 2002. Calculations give minimum denudation rates of 0.21 mm per 1000 years for the entire seven-year period and 0.42 mm per 1000 years for the period between 1998 and 2002. This means that almost all loss of material occurred during the last four-year period. There are fairly large areas displaying a shallow downwearing. These areas are mainly situated at painted parts of the rock carving. Of this reason it is difficult to assess whether the detected surface lowering is due to real rock breakdown. The figures have been repainted between the measurements and old and new paint might have varying thickness. There are, however, some minor places where the weathering has reached a depth of more than one mm. At those places single mineral grains have been lost from the coarse grained granite. The values from the roughness calculations (table 3 & 4) show a low standard deviation as well as almost neutral skewness and kurtosis. This indicates that the entire surface has similar characteristics. The mean and median values show that the surface has some granularity and is not completely smooth. In the calculations based on squares sized 10x10 mm the minimum value is very low, due to smooth surfaces of the red paint.

It can be concluded that the rock carvings at Gryt 1 (Frännarp) at present are in a good state, and calculated present denudation rates are not alarming. Especially not since most of the detected breakdown is due to repainting of the figures. Some shallow granular disintegration has, however, been detected. There is a real risk that the loss of single mineral grains will proceed at a faster rate in the future. The moist environment with precipitation of organic material might also influence the downwearing at the rock carvings negatively in coming times.

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Figure 9. Digital shadow image of a carriage made in coarse-grained granite at Frännarp in the parish

of Gryt, county of Skåne. The imaginary light comes from the NE.

5.3.2. Järrestad 13 (Dansarenhällen), Nr 5

The locality lies in a fenced area only grazed by horses in autumn, when there are not so many visitors. It consists of a several 100 square m big outcrop with an inclination of a few degrees towards ESE. A large number of carvings of spirals, snake-like figures, foot soles and ships are present. There is also a large man figure called ‘the dancer’, from which the place has got its name. The area seems to be in a good state and the shallow rock carvings are easily seen in the quartzitic rock. In contrast to other places of great public interest there has not been any need to paint the figures. Glacial striations in direction 60º are obvious and there are other signs of small-scale glacial erosion as well. Natural joints are common and the spacing between them is typically 20 to 30 cm. Limited lower vegetation is concentrated to these joints and, for example, lichens are sparse on other areas.

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Figure 10. Distribution of roughness values from the micro mapped site Järrestad 13 (Dansarenhällen),

based on calculations from squares sized 10x10 mm with one height recording on every square mm.

The majority of the values lie between 15 and 30 showing the fairly smooth main surfaces of the

quartzite. The higher values forming the tail to the right indicate major irregularities, mainly due to joints.

Measurements were made at Järrestad 13 in August 1995, August 1998 and June 2002 over an area with some distinct joints and a snake-like figure. Very high downwearing rates result from the calculations (between 1.47 and 1.54 mm per 1000 years). When viewed in more detail and compared to images derived from the micro mappings and photographs it is seen that all material loss is detected at the joints. Some downwearing might occur here, but the main reason for the high breakdown rate that was calculated is the limitations of the triangulation laser used in the project. These limitations are described in the chapter 3 about ‘Methods for field measurements’ on page 9. It can therefore be concluded that present downwearing rates are fairly low and the material loss at joints is far lower than calculated. The roughness distribution is shown in figure 10, and seen in table 3 & 4. The majority of the areas are fairly smooth, but not as smooth as can be expected directly after glacial polishing of the rock surfaces. The higher values indicate areas at joints. Both the distribution calculated from squares sized 10x10 mm and squares sized 20x20 mm are due to the presence of the joints highly positively skewed. The kurtosis and standard deviation are as well high.

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Although quartzite is a hard and durable, the Bronze Age rock carvings will ultimately be obscured and finally disappear in this environment, even if it goes slower than at other places. There are signs that some downwearing occur at cracks, and main areas are also affected by initial weathering. The surfaces of the rock have attained a slightly darker colour than the initial quartzite. As revealed by the roughness calculations some of the initial smoothness of the rock has most probably got lost after the land ice left the area. There are some minor scars indicating that a few tiny fragments have been lost from the rock surface.

Table 2. Sites where micro-mappings have been performed at only one occasion. The co-ordinates are

in ‘Rikets Nät’ (RT90). The sites are not marked on the map in figure 5, but their position can be found

with help of the co-ordinates. The rock carvings g to m in Västra Götalands län are all measured with a

prototype device in 1992 or 1993. The size of the measurement quadrangles is also indicated.

County Site Size (cm3) Co-ordinates

Skåne län a. Simrishamn 23 225 6157565 1408478

Stockholms län b. Turinge 441 600 6564430 1594905

Södermanlands län c. Nicolai 340 (Släbro, Nyköping) 725 6517198 1567884

Uppsala län d. Boglösa 138 (Rickeby, mantle) 500 6610504 1574973

e. Boglösa 141 600 6610415 1574802

Västra Götalands län f. Husaby 70 (Flyhov, circle-cross) 462 6492690 1359757

g. Skee 614 (Massleberg) 382 6546243 1241966

h. Tanum 12 (Aspeberget, bull figure) 430 + 769 6516714 1241168

i. Tanum 12 (Aspeberget, circle-cross) 528 6516714 1241173

j. Tanum 18 (Aspeberget, ship) 800 6516571 1241239

k. Tanum 26 (Aspeberget, horse) 980 6516517 1241187

l. Tanum 72 (Tegneby, mellangården) 194 6516101 1240414

m. Tanum 417 (Kalleby) 839 6512562 1242304

n. Tisselskog 12 (Högsbyn, footsole) 306 6535082 1302516

Östergötlands län o. Östra Eneby 1 (Himmelstalund) 144 + 627 6496801 1519742

p. Östra Eneby 8 (Fiskeby) 196 + 196 6497022 1518215

q. Östra Eneby 23 (Ekenberg) 440 6497620 1517609

5.3.3. Simrishamn 23, a

The outcrop lies next to a stone quarry and the distance to the Baltic Sea is only about 50 m. Other characteristics of the site are similar to those at Järrestad 13 (Nr 5), with distinct signs of glacial erosion and natural joints. One disadvantage is that there are several

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carvings of signatures and figures made with machinery in the 20:th century disturbing the original environment.

Only one micro mapping was made (August 1995), and hence no calculations of material loss were possible to make. The measurement was performed over a figure of a standing man holding an axe bigger than he was himself. The slope here is 5º towards ENE. The roughness calculations are seen in table 5. Since no major joints are present in the measured area the statistics differs from them at Järrestad 13. The median value is similar, but the standard deviation is low and the skewness as well as the kurtosis is nearly neutral. This reflects that there are similar characteristics over the entire surface. As at Järrestad 13 it is from the roughness values seen that the rock surfaces are not perfectly smooth. Unevenness caused by the measured figures and by tiny fragments chipped away some time after the ice age is revealed.

Table 5. Statistics from surface roughness calculations at rock carving sites where only one

measurement has taken place. The calculations are based on 100 evenly distributed height values in

squares sized 10x10 mm.

Site Min Max Mean Median 1:st qu 3:rd qu skew kurt

Simrishamn 23 17.32 33.55 23.49 23.39 21.37 25.17 2.96 0.49 0.58

Turinge 441 9.75 42.01 17.01 15.44 13.11 19.85 5.47 1.91 5.29

Nicolai 340 9.65 121.80 23.45 16.83 14.29 20.91 19.80 3.10 10.04

Boglösa 138 12.72 120.85 31.92 26.88 21.04 36.07 18.12 2.36 6.76

Boglösa 141 9.91 52.66 22.56 21.19 17.73 26.33 7.04 1.28 2.75

Husaby 70 4.49 37.24 16.73 15.99 9.24 22.69 7.72 0.37 -0.78

Skee 614 6.71 23.55 12.76 12.03 10.65 13.99 3.16 1.15 1.68

Tanum 12 (bull-92) 12.60 54.76 23.36 22.84 19.10 26.11 5.86 1.83 6.91

Tanum 12 (bull-93) 12.85 78.88 33.93 30.89 25.25 40.37 12.28 1.15 1.44

Tanum 12 (cross) 8.19 56.51 18.15 16.89 14.49 21.26 5.71 2.53 13.45

Tanum 18 12.06 51.26 22.98 21.85 19.07 26.41 6.15 1.19 2.99

Tanum 26 4.98 33.86 13.35 10.65 8.63 18.33 6.11 0.94 0.06

Tanum 72 6.79 32.06 17.78 17.47 13.99 20.30 4.72 0.56 0.26

Tanum 417 15.60 51.35 28.07 27.20 23.19 32.36 6.68 0.62 0.34

Tisselskog 12 6.28 68.37 22.94 22.17 14.88 29.59 9.87 0.83 1.87

Östra Eneby 1 (animal) 6.02 120.22 20.50 15.80 10.81 23.29 17.05 3.53 16.11

Östra Eneby 1 (ship) 7.78 40.33 20.70 19.92 16.18 24.17 6.44 0.78 0.63

Östra Eneby 8 (I) 4.67 18.42 8.35 7.85 6.73 8.78 2.54 1.80 3.54

Östra Eneby 8 (II) 4.47 29.97 7.67 7.26 6.34 8.22 2.61 4.99 38.42

Östra Eneby 23 10.93 69.36 27.32 25.69 20.91 31.78 9.99 1.17 2.28

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About the future decay at the site similar conclusions can be drawn as for the other investigated quartzite area. Some deterioration occurs at joints and a few minor rock fragments will be lost from the area also during coming times, although this goes slower than in most other rock types. A negative factor at Simrishamn 23 is the nearness to a sea with brackish water, since salt spray might speed up the weathering process.

5.4. Stockholms län In the county of Stockholm repeated measurements have been made in the parish of

Ösmo, near the town Nynäshamn. The rock in this area consists of Precambrian marble that partly can be dolomitic. The marble is crystalline and usually medium-grained, but variations occur. Near the measurement site CaCO3 dominates strongly compared to MgCO3. Analyses reveal 88.2% CaCO3, 0.5% MgCO3, 0.1% iron and aluminium oxides and 11.0% insoluble components (Stålhös, 1979). The folding is often complicated and the rock is associated with banded red leptite. Granular quartz inclusions, varying in size from a few mm up to half a meter, are also significant. In Turinge, a few km W of the town Södertälje a micro mapping was done at one occasion. The bedrock here is from Lower Svekofennian and consists mainly of greywacke, schist, quartzite and arkose metamorphosed to gneiss and migmatite.

5.4.1. Ösmo 622, Nr 6

Still preserved rock carvings in carbonate rock are not common in Sweden, and this is the main reason for investigations at Ösmo 622. Quartz nodules and other inclusions protrude sometimes several cm above the marble. There are also signs of minor karst weathering (karren). The outcrop with mainly ship carvings lies at the edge of a summit about 50 m from a larger road. The slope is unusually high, 40º towards E. The surroundings are used as grazing land, but animals does not pass the steep rock carving site.

Measurements were made in July 1996, October 1999 and August 2002 over a deeply cut ship, but with fairly unclear contours. There were great difficulties in placing the laser scanner device stable during measurements due to the steep inclination. Of this reason the three measurements are considerably bent and turned compared to each other. Studs were as well not attached to the rock at this site. Instead the normally resistant quartz nodules were thought to serve as fix marks. However, breakdown occurred here as well due to their granular structure. Together with the bad overlap of the images, with great parallax errors, this made it impossible to superimpose the consecutive measurement data files satisfactory for calculations of material loss. Nevertheless there are three good micro maps of the area, from three occasions, where minor details can be compared to each other although quantitative calculations can not be made. For example, a few cm wide runnel just above the ship figure has clearly been widened between 1996 and 2002. Other changes are also possible to detect. When the roughness statistics are viewed (table 3, 4 & figure 11) it can be seen that the mean and median values at Ösmo are among the highest of all investigated sites. This describes the irregular micro topography caused by the deeply incised ship figure and especially by the protruding quartz nodules.

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Most probably there is a high downwearing rate at Ösmo 622, although it has not been possible to prove this by any calculations. One important factor for weathering in limestone areas is, together with other weathering types, solution. Dissolved Ca2+ disappears, for example, with rainwater draining the area. Some minor karren forms are evidences of the solution effect, as well as the widening of a small runnel in the micro mapped area and the unclear contours of the ship figure despite its depth. By solution it might well be that some figures are deepened and at the same time widened, thus obscuring them before they disappear. This effect, however, also means that the outline of the figures to some extent survives for a longer time than can be expected from the downwearing rate alone. The solution of limestone also leads to collapse and loss of quartz nodules and other insoluble components.

Figure 11. Distribution of roughness values from the micro mapped site Ösmo 622, based on

calculations from squares sized 10x10 mm with one height recording on every square mm. It can by the

high average be seen that the entire surface has a pronounced micro topography that is due to a deep

ship figure and to protruding quartz nodules.

5.4.2. Turinge 441, b

The measurement site lies on a small outcrop, about two m from its summit, and the slope is 10º towards N. The vegetation in the immediate vicinity is sparse and the distance to a motorway is about 200 m. The rock carving seems to be in a good state and the contours of the fairly shallow cut ship are clearly visible. The roughness statistics in table 5 show low mean and median values indicating mainly smooth surfaces. This can also be interpreted as a relatively low degree of weathering. Most probably the good state of this carving will be preserved for a relatively long period if environmental factors not are changed in a negative way.

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5.5. Södermanlands länIn the county of Södermanland two areas were micro mapped at a site in the parish

Nicolai in the town Nyköping. On one of them repeated measurements for calculations of material loss were made. The bedrock in the area consists of gneissic granodiorite and light tonalite. Migmatite and metabasite dikes are also present at several places (Lundström, 1974).

Figure 12. The site where repeated micro mappings have been made at Nicolai 340 (Släbro) in

Nyköping. The damaged parts beneath the net figure are easily recognisable. Two of the small studs

used for repositioning of the laser equipment are also seen on the photograph.

5.5.1. Nicolai församling 340 (Släbro), Nr 7 & c

In a park, surrounded by villas and a school, at Släbro (Oppeby) in the town Nyköping there are some flat outcrops with a large number of rock carvings of mainly net figures. They were discovered in 1984 (Wigren et al., 1990), and in contrary to other places the figures are painted white instead of red to display them for the public. There are, as seen in figure 12, several damaged areas that have destroyed the original figures. The form, with less deep material loss at the edges than at the centre of the destructed parts, indicates that

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they have been caused by fire. Usually when natural exfoliation occurs flakes with an even thickness are lost from the upper part of the rock. There are no signs that the damages are enlarged at present, and areas where still remaining sheets have lost contact with the underlying rock are minimal. At the edge of the grass beneath the outcrops some down-washed rock fragments are found, but the extent is limited. Quartz veins can at some places be seen to protrude a few mm above the rest of the rock, indicating a minor weathering since the area rose above the sea. Up to 1996 the lichen cover was extensive. After that, parts of the rock carvings were covered for several years, which made the lichens disappear.

The gneissic area in figure 12 was investigated and micro mapped in September 1994, June 1996, June 2000 and in May 2002. The rock slopes 5º towards WNW at this place. Calculations reveal minimum denudation rates of 0.24 mm per 1000 years for the period 1994 to 2002, 0.28 mm per 1000 years between 1996 and 2002 and only 0.04 mm per 1000 years between 2000 and 2002. Most of the indicated material loss is found at the abrupt edges between preserved and damaged areas. The measurement method might, however, at such places give misleading results due to, for example, unwanted reflections. There are also areas displaying a shallower downwearing, on overlays for the periods 1994 to 2002 and 1996 to 2002. These are due to lichens that were not possible to remove completely during the first two measurements. As mentioned above the lichens disappeared after the temporary covering of the site. The conclusion is that hardly any surface lowering is taking place at present at the investigated site. The roughness calculations (table 3 & 4) show fairly low minimum and 1:st quartile values, indicating that main surfaces are smooth and in a relatively good state. The abrupt edges towards damaged parts give considerably higher roughness indexes, also causing high overall skewness and kurtosis values.

Table 6. Statistics from surface roughness calculations at rock carving sites where only one

measurement has taken place. The calculations are based on 100 evenly distributed height values in

squares sized 20x20 mm.

Site Min Max Mean Median 1:st qu 3:rd qu skew kurt

Nicolai 340 12.10 265.54 43.94 28.34 22.39 54.29 38.24 3.06 12.26

Boglösa 138 18.86 132.92 50.70 46.44 35.23 59.11 21.06 1.39 2.33

Boglösa 141 17.21 134.14 42.02 39.84 27.91 49.47 18.44 1.74 5.66

Husaby 70 6.73 63.56 29.08 31.22 20.85 35.23 11.71 0.15 0.30

Tanum 12 (cross) 12.38 93.72 27.36 24.91 20.69 32.22 11.25 2.65 12.41

Tanum 18 15.45 62.18 35.36 34.52 30.05 40.24 8.11 0.57 0.61

Tanum 26 6.79 48.94 15.95 11.49 10.29 21.53 8.50 1.33 1.03

Tanum 417 22.56 90.92 40.20 37.52 32.43 45.27 10.89 1.45 3.73

Östra Eneby 23 20.59 310.17 58.04 45.86 35.28 59.86 46.50 3.57 14.07

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In September 1994 another site, about 5 m NNW of the other was micro mapped. The slope is here 12º and the rock is mainly metabasite with pegmatite in the upper right part of the measurement quadrangle. Damages are abundant, and only minor parts of the rock carving are preserved. Roughness statistics are presented in table 5 & 6. Minimum, mean and median values are lower in the metabasite here than in the gneissic part of the outcrop, while the other parameters are similar. The reason is that dark, basic rocks often display smoother surfaces than light, acid or intermediate ones although deterioration has acted in similar ways.

It can be assumed that no dramatic changes will take place at the investigated area in the near future. As at all other places some rock breakdown is, however, always taking place. Unfortunately large damaged areas are present at the outcrop even if there are no signs that they are extending at the moment.

5.6. Uppsala län All five measurement sites in the county of Uppsala lie in the vicinity of the town

Enköping. At three of them repeated measurements, for assessing the downwearing rate, have been made. The bedrock in the area consists of Svekofennian supracrustal rocks (Stålhös, 1974 & 1976). Mica schist, that often is more or less gneissic and has a convoluted strike, is most abundant. There is also a fairly well preserved plagioclase quartzite in mixed layers with the mica schist. Other features of the bedrock are veined gneiss, pegmatite veins and locally quartz diorite as well as granodiorite.

5.6.1. Boglösa 138 (Rickeby), Nr 8 & d

The rock carving field Boglösa 138 at Rickeby lies on a roche moutonnée with distinct glacial striations. Discolouration of rock surfaces is a common feature and there are several places where exfoliation has occurred. At some damaged areas minor parts of the rock can be seen to have been detached by weathering and erosion. The lichen growth is also fairly dense.

A ship figure, with somewhat diffuse contours but still clearly visible, has been micro mapped at seven occasions. This was in September 1994, August 1995, July 1996, June 1997, August 1998, September 1999 and in August 2002. The slope at the site is 12º towards NE. About one third of the measurement area displays initial exfoliation. Here the surface layer of the rock is bulging up, leaving a hollow space between the uplifted sheet and the rock below. The extent of the affected area can easily be revealed by knocking. No part of the exfoliation sheet has yet been lost, and therefore the thickness of the sheet and the hollow area beneath it can not be estimated. The reason why this site was measured more frequently than other places was to follow and monitor the progress of this specific weathering process, exfoliation. It is both from a scientific and conservationist view interesting to study whether the loosened sheet would continue to expand and bulge up before complete failure occurs. A better knowledge of the process can make it possible to take conservation precautions at other places with similar phenomena. In the left part of the measurement area, crossing the ship figure, there is a joint.

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Figure 13. Contour map of the upper left corner of a rock carving at Boglösa 138 (Rickeby), interpreted

as a chair or a mantle. The contour interval is 0.5 mm. Deeper parts of the figure are also shown with

darker shades of grey.

The micro mappings show that there is no evidence of significant surface changes, such as upheaval, at that part where exfoliation has started. Calculations of material losses give somewhat varying results, between 1994 and 1999 as well as between 1998 and 1999 the computed surface lowering is less than 0.01 mm per 1000 years. From 1997 to 1999 it is 0.05 mm per 1000 years and from 1995 to 1999 0.22 mm per 1000 years. The calculated downwearing rate for the period between 1996 and 1999 is considerably higher, 0.71 mm per 1000 years. Almost all calculated material loss has occurred only at the joint crossing the measurement area. This is not a sign of a real downwearing. The discrepancies between the calculations from different periods are instead due to placements of the laser equipment at slightly different angles towards the rock surface at different measurement occasions. This causes parallax errors and unwanted false reflections that are most noticeable at the joint. For the period between 1999 and 2002 the calculated denudation rate was 0.64 mm per 1000 years for the lower 2/3 of the measured area and 0.38 mm per 1000 years for the upper 1/3. This material loss is shallow and has happened at other places than at the joint.

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Although some material loss can have occurred during this period it is most likely that the calculation results are due to a more thorough cleaning before the last measurement. Hereby lichens have been better removed than at earlier micro mappings. The micro topography caused by varying resistance to weathering of different minerals of the rock and the presence of a joint in the measurement area is clearly depicted by the roughness statistics in table 3 & 4.

In September 1994 a part of another rock carving on the same outcrop was micro mapped. At this place there is a gentle slope towards SW. The figure is difficult to interpret, but it could be a ceremonial seat or a cloak, in natural size, stretched out on the rock (Coles, 1994). As seen on the contour map in figure 13, the lines of the figure are about 50 mm wide and more than 8 mm deep. The roughness statistics (table 5 and 6) is very similar to that from the ship figure a few m apart. This is especially true for the roughness values based on calculations of squares sized 10x10 mm. The same type of micro topography and minor weathering phenomena on the two measured areas are thus clearly revealed by the roughness calculations.

There has not been any dramatic rock breakdown during the monitoring period at Boglösa 138 (Rickeby). There are, however, fairly many signs of present weathering at the site. This means that the situation and state of the rock carving field might deteriorate in the near future. For example, at the micro mapped ship carving the still present uplifted exfoliation sheet can fail and collapse very quickly. Trampling or even vandalism can make it occur earlier than natural processes alone. On other parts of the outcrop holes through areas with exfoliation are observed. The chair or mantle figure will on the contrary, since it is very deeply carved, withstand even severe weathering and erosion and hence be preserved for a long time.

5.6.2. Litslena 194 (Ullstämma), Nr 9

In a closed pasture at Ullstämma in the parish of Litslena mostly ship figures and cup marks are present on a fairly flat lying outcrop. The area, having a dense lichen cover, is not in a good state and the rock surface is severely damaged at several places. Micro mappings were made in August 1995, June 1997 and August 2002 of a ship where central parts have been lost by flaking. The slope at this place is 10º towards NNW. When the site was prepared for measurements some loose lying fragments were observed at the edges of the exfoliated area.

The calculated downwearing rate for the period between 1995 and 2002 is 1.11 mm per 1000 years while it is 0.10 mm per 1000 years between 1997 and 2002. This means that practically all detected material loss took place before 1997, showing the in time intermittent rock breakdown that is caused by weathering. The downwearing was most pronounced along the edges of parts where flaking already had occurred. This means that already present damaged areas were enlarged. As can be seen in figure 14 there are several places were the surface lowering is about 2 mm during a two-year period. There are also clearly detectable downwearing at some other spots. Areas where only minor surface lowering is detected can be due to differences in the thickness of the lichen cover at the measurement occasions. The cover was difficult to remove completely. The roughness data

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(table 3 & 4) indicate that large areas have a fairly smooth micro topography, but they also indicate the marked edges between parts where flaking has taken place and still present older rock surface.

The micro mapped ship figure is obviously under a state of present destruction and further enlarging of exfoliated areas will make it disappear completely. The surface layer on large parts of the rock seems to be fragile due to alteration. This means that many figures are endangered. Deeper rock carvings, such as cup marks, will, however, be preserved for a longer period. One reason for cup marks being a very common type of rock carving might indeed be that they can be found on rocks where other figures already are gone due to weathering.

Figure 14. Material losses to depths of more than 0.5 mm during the period 1995 to 2002 at Litslena

194 (Ullstämma). The contour interval is 0.25 mm. The major rock breakdown took place along the

edges of areas already destroyed by flaking. Almost all material loss at the site occurred between 1995

and 1997.

5.6.3. Vårfrukyrka 192 (cup marks), Nr 10

This measurement site in the parish of Vårfrukyrka consists of an area with a large number of cup marks. Before the first measurement an about one cm thick layer of soil had

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to be removed. Such a thin covering is not protecting the ancient remains, instead it can cause that moisture is preserved a longer time. The cup marks themselves were also filled completely with soil. There are several macroscopic signs that weathering is active. Rust coloured surfaces are common and loose mineral grains derived from the, often soft, surface of the rock are seen at many places. There are also several a few mm high abrupt edges that can be signs of flaking. Another possibility is that the edges were created by rock failure already when the cup marks were made. The entire outcrop lies fairly flat and grass is growing immediately next to it. The area is used for grazing by heifers. After rainfall the cup marks become filled with water that remains for a long time. They also quickly become filled with fine-grained material. These two factors can cause the weathering to go faster in the cup marks themselves than on the adjacent rock.

Figure 15. 3-D model in orthogonal projection of the measurement site Vårfrukyrka 192, with cup

marks. The vertical exaggeration is two times and the contour interval 1 mm.

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Measurements of the area shown in figure 15 were made in September 1994, July 1996 and August 2002. When calculations are made of the downwearing rate between 1994 and 1996 the figure is unusually high, 12.98 mm per 1000 years. Material loss has especially been detected from the bottom of the cup marks, while significant changes not can be seen along the sharp edges, mentioned above. Due to the great height differences within the micro mapped area it has been difficult to make a good overlap of images from consecutive measurements, and parallax errors are obvious. Although there is a fast denudation the calculated surface lowering is, most probably, an exaggeration of the true downwearing rate. It was not possible to overlap the micro map from 2002 with the two older ones. When details are compared it can, however, be seen that that rock breakdown has continued after 1996, but with a slower rate than before. Minimum and median values in the roughness statistics (table 3 & 4) are high. The reason is the several cm deep cup marks. Since they are the main topographical feature of the rock surface the skewness and kurtosis values are near neutral.

There is continues weathering at the investigated site, and there is no reason to believe that downwearing rates will decrease in the future. Such figures as cup marks might be preserved for a long time even at places where rock breakdown is intense. There is a possibility that they weathers, and deepens, faster than the surrounding surfaces are lowered. If other rock carving figures have been present at the site they would already have disappeared at this intensely weathered area.

5.6.4. Boglösa 141, e

The outcrop is low and fairly flat, with ship figures as the most common rock carving. According to Coles (1994) about 250 figures have once been present at the site, but many of them are gone. The general impression is that the rock is fairly fragile and susceptible to weathering. In September 1994 a micro mapping was made of a ship on the lowest part of the outcrop. It is deeply carved, but its edges are diffuse, and the surrounding rock has a smooth appearance. A drive goes straight over the measurement site. The roughness data in table 5 & 6 indicate that the area indeed is smoother than the other micro mapped places in the vicinity of Enköping in the county of Uppsala. The difference compared to the two sites at Boglösa 138 and the site at Vårfrukyrka is especially distinct. On a fairly soft rock like this the smoothness can possibly have been created by anthropogenic abrasion caused by vehicles on the drive. It is important that ancient cultural remains not unnecessary have to suffer any influence that can make the always present downwearing go faster than by natural processes alone.

5.7. Västra Götalands län, province of Bohuslän In the province of Bohuslän repeated micro mappings, for assessing material loss, have

been made at six sites and at a total of eight measurement quadrangles. Seven further places that have been recorded with the laser scanner equipment at one occasion are also described. The reason why there is some concentration of research effort in N Bohuslän is the importance of the region. It is the main rock art area of all Scandinavia, and perhaps

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even of Europe, with more than 1000 sites with together more than 40 000 rock carvings (Bertilsson, 1987). The area around the parish Tanum is on the UNESCO world heritage list. The majority of the carvings are Bronze Age and there is a rich variety of figure types. Among them are, for example, ships, humans, footprints, animals, circles, ring-crosses and cup marks.

Main parts of Bohuslän can be interpreted as a Mesozoic etched joint valley landscape (Lidmar-Bergström, 1995), with major joints mainly in N-S, NNE-SSW and WNW-ESE. Often minor joints also have the same directions. The investigated rock carving in the parish of Foss (Lökeberg) lies in an area with grey, usually veined, orthogneiss (Samuelsson & Lundqvist, 1990). All micro mapped sites in the parish of Tanum, the two sites in the parish of Brastad and the site in the parish of Skee are all carved in, so called, Bohus granite. The measured places in Tisselskog are situated in the province of Dalsland and Husaby (Flyhov) in the province of Västergötland. These sites are described later in this report. The Bohus granite occupies an area of about 2000 km2 in Sweden and Norway, and has a U-Pb age of 920x106 years (Eliasson & Schöberg, 1991). It consists of a number of granite intrusions with slightly varying petrography and chemistry, generally monzogranite. The texture and colour varies, however, considerably, with a red to greyish- red, medium-grained, biotite granite as the dominating rock type. In some areas there is also a greyish-white, medium-grained, ‘two-mica’ granite (Eliasson et al., 2003). Pegmatite and aplite dykes are fairly common.

5.7.1. Brastad 141 (man with big hand), Nr 11

The micro mapped rock carving lies on an almost flat outcrop, measuring about 1.5x5 m, surrounded by grass and mainly deciduous trees. It is situated a few tenths of m away from a road and at a level about four m above it. There are ‘original’ surfaces with still preserved micro glacial striations on the fine-grained granite. The boundaries of the mineral grains do, however, not always look fresh and a limited number of grains are detached from the rock when the surface is prepared for measurements. When holes for the small studs, used as fix marks, were drilled into the granite adjacent to the rock carving it was noticed that the upper few mm were fairly soft. This indicates that the surface has undergone alteration due to weathering.

Measurements were made of a shallow rock carving of a man with one very big hand (figure 16) in September 1995, August 1997, August 2001 and in August 2002. Unfortunately only the first two laser scans were fully successful. It was only possible to use parts of the micro maps from 2001 and 2002. In all calculations no downwearing to depths of more than 0.5 mm could be detected, and hence the present surface lowering is very limited. Between 1995 and 1997 the material loss to depths of more than 0.25 mm only amounted to 36 mm3. When compared to other granite sites it can be seen that the roughness calculations (table 3 & 4) result in lower values than elsewhere. The micro topography on the outcrop is due to, only small, differences in height between the ‘original’ surfaces and places where mineral grains have been lost.

Although significant material loss could not be detected by the micro mappings, and the site at present is in a good state, it can by no means be considered safe for rock breakdown

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in the near future. The surface is soft and some mineral grains are lost. Because of the fine-grained rock it might be that the minor granular disintegration that obviously occurs not has been detected with the resolution that was used during the laser scans. Precipitation of needles and leaves on the rock surface, and maybe the location of the area in the major wind direction from an oil refinery at the nearby town of Lysekil, are other factors that can influence the course of weathering negatively.

Figure 16. Image of a shallow rock carving of a man with one big hand at Brastad 141. Darker shades

of grey indicate greater depths. Are there six fingers on the hand, or is the sixth finger only due to a

minor groove in the granite?

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5.7.2. Brastad 18 (deer figure), Nr 12

The rock carvings at Backa in the parish of Brastad were among the first to be discovered in Sweden. The investigated outcrop lies immediately next to a road. Where water frequently trickles over the rock surface there is a brownish or black discoloration. Both needles and leaves are falling down on the outcrop. Despite these risk factors the general appearance of the site is that it is in a good state. Glacial striations are clearly visible, but ‘original’ surfaces are, however, not obvious. The direction of the striations has been utilised when making the rock carvings.

Micro mappings were made of the magnificent horns of a deer in September 1995, July 1997 and August 2001. Joints are present on both sides of the horns. The slope of the outcrop is generally marked and is 12º towards ESE at the measurement site. The detected material loss to depths of more than 0.5 mm is limited, and only two minor spots are affected. Calculations give downwearing rates of 0.01 mm per 1000 years for the entire six-year period and 0.10 mm per 1000 years for the period between 1997 and 2001. Mean and median roughness indexes (table 3 & 4) are higher than at Brastad 141, reflecting the coarser grain size and hence slightly more pronounced micro relief of the granite near the deer figure. The presence of joints is also depicted by the roughness statistics.

When the results from the laser scanning and other observations are considered it could be concluded that dramatic changes in downwearing rates would not take place in the near future. There are, however, some risk factors. The minor weathering phenomena and the precipitation of needles and leaves are already mentioned above. Salting of the road beneath the rock-carving field during the winter can be potentially dangerous. Due to the traffic salt may then be sprayed upon the rock surface, and it is known that salt weathering is an effective downwearing agent. At this place it is, however, of limited importance since the number of cars on the road is relatively small.

5.7.3. Foss 6 (Lökeberg), Nr 13

The site at Lökeberg in the parish of Foss is situated near the municipality Munkedal, S of the area with Bohus granite. It lies at the edge of arable land and the rock is plastically sculptured by glaciofluvial melt-water. The figures on the panel are often cut to depth of more than one cm, but despite this their contours are usually not very distinct. The lichen growth is extensive and it reappears completely in a few years time after cleaning. There was very little resistance when the holes for the fix studs were drilled, indicating that the rock is soft and probably porous as well. The appearance of the surface of the gneiss is also fairly rough. These factors mean that alteration and weathering already have affected the area considerably.

The entire outcrop has a marked slope, and at the measurement site, consisting of a ship figure, it is 28º towards SE. The micro mappings were made in August 1996, August 1998 and in August 2002. The calculated denudation rate between 1996 and 2002 was 3.73 mm per 1000 years, which is a very high figure compared to most other investigated rock carvings. The figure is, however, by no means unreasonable. The micro map from 1998 could not be exactly overlapped with the other two maps. A comparison shows that the deepest damage to the left in the measurement area, seen in figure 17, was created already

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between 1996 and 1998. Although a fast rock breakdown can be ascertained the calculated figure probably exaggerates the speed of surface lowering. The density of the lichen cover and problems in removing it completely declines the accuracy of the calculations. The values from the roughness statistics (table 3 and 4) are among the highest of all measured sites. This is due to the generally rough rock surface and to the great depths of the micro mapped ship figure.

Figure 17. Material losses to depths greater than 0.5 mm at Lökeberg in the parish of Foss between

1996 and 2002. The contour interval is 0.25 mm. Major rock breakdown has occurred at a spot in the

central left part of the measurement area between 1996 and 1998 and at the right part of the bottom

during the entire period. Where a more shallow material loss is indicated the reason might be due to

lichens remaining on the rock surface when the first laser scan was made. The surface lowering shown

on the picture is therefore probably exaggerated compared to the real material loss.

The present downwearing at the site is substantial and it can be expected to continue at similar rates in the future. Due to the great depth of the carvings the figures themselves will, however, remain for a relatively long time. The extensive lichen growth and the ease by which the lichens colonise the porous surface layer of the rock are other indicators of a

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fast present weathering rate. It seems that the deterioration rather proceeds by granular disintegration than by the loss of rock fragments containing several mineral grains.

5.7.4. Skee 614 (Massleberg), g

The rock carvings at Massleberg in the parish of Skee are generally well preserved. Among the figures are ships, animals, a hunting scene with deer and dogs, humans and a peculiar sun symbol (Coles, 1990). He also mentions that parts of the rock exhibit damaged areas that are believed to be due to fire. Plastic sculpturing by glacial melt water is evident above the carvings and micro glacial striations are seen here as well as on other places. These ‘original’ surfaces indicate that downwearing during Holocene has been very limited. Parts of the outcrop are, however, covered by lichens.

A single micro mapping was made, with a prototype of the laser scanner equipment, in 1993 of an area with a slope of 8º towards NE. Within the area parts of a ship and some cup marks are present. From the roughness data in table 5 it is seen that the rock is very smooth, by the low mean and median indexes. The collected height data from the prototype device had to be recalculated in order to compare results with those from later measurements. The reason was that the measurement resolution in the x- and y-directions was slightly different from those used from 1994 and onwards. These calculations might have resulted in somewhat lower roughness indexes than the real ones. Nevertheless it can be concluded that the site Skee 614 (Massleberg) has one of the absolutely most even micro reliefs of all investigated granites.

Since the rock is in a good condition and there are few signs of weathering it is fairly certain that observed damaged parts are due to fire, as also is the case at the investigated rock carving at Släbro in the town Nyköping (page 38). If flaking, caused by weathering processes, is present there should most probably also be other signs of alteration and a more pronounced micro relief would have been revealed by the rock roughness data. There is as well no evidence that damaged areas presently are becoming larger. The conclusion is that there is no reason to believe that the rock carvings will deteriorate considerably in the near future.

5.7.5. Skee 619 (Jörlov), Nr 15

The rock carvings at Jörlov in the parish of Skee lie behind an outbuilding of a formal farm. The granite at the site displays intense granular disintegration and single mineral grains and a few mm big rock fragments are scattered all over the outcrop and are accumulated at the edge of the grass beneath the rock carving field. It seems that the deterioration mainly takes place by granular disintegration and by some kind of ‘micro exfoliation’, where about one mm thick flakes with sizes around one cm detaches from the rock. The scars, where flakes newly have disappeared are easily seen macroscopically since they are lighter in colour than the rest of the rock surface. When a flake has disappeared from one place, the weathering usually continues at another place. This process leads to a fairly uneven micro relief. There are virtually no lichens at the site. When interpreted in a

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negative way this can imply that the weathering is so fast that there is not enough time for the lichens to colonise.

Micro mappings were made over an already almost disappeared ship figure in May 1995, June 1996, August 1997 and in June 2002. The slope here is 16º towards ESE. Calculated weathering rates are similar for all periods between the measurements, and vary between 1.79 and 2.13 mm per 1000 years. The downwearing has thus proceeded with an even speed at this site during the seven year long monitoring period. How it has occurred spatially is seen in figure 18. Since there are no abrupt edges and lichens at the rock carving, disturbing the laser scanning, the calculated rock breakdown is accurate. The roughness statistics in table 3 & 4 indicate that the micro relief due to the present weathering is fairly rough and that characteristics are similar over the entire surface since the skewness and kurtosis are low.

Figure 18. Surface lowering to depths of more than 0.5 mm at Jörlov in the parish of Skee between

1995 and 2002. The contour interval is 0.25 mm. The downwearing mainly proceeds by detachment of

thin rock fragments of a few cm in size. The rates have been similar throughout the entire period.

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The figures on the panel are hardly recognisable anymore and it can be expected that breakdown will continue at a similar speed also in the future making the rock carvings disappear completely in a relatively short time. This will occur although the calculated downwearing rates are not extreme. They are near to the average that is estimated for Scandinavian crystalline rocks of one to two mm per 1000 years.

5.7.6. Tanum 12 (Aspeberget), Nr 16, h & i

The rock carving fields at Aspeberget, near the Vitlycke rock art museum, are among the richest and most important in Sweden. The state of the granite is here, however, varying. There are areas where the rock looks almost fresh and adjacent to them are areas exhibiting intense weathering. Observed weathering features are, among others, granular disintegration and ‘micro exfoliation’ in the form of thin and tiny fragments that are detached from the rock. The latter type of weathering has also been observed at Jörlov in the parish of Skee (page 50) and at an experimental field at Litsleby in the parish of Tanum. The area at Litsleby has no known rock carvings and a wide variety of experiments in order to study weathering processes, their causes and methods for protecting the granite from further breakdown have been carried out here. Furthermore the potassium feldspar at Aspeberget can often be seen to protrude somewhat from the rest of the rock and this mineral has in many cases attained a whitish colour, indicating an initial alteration. There are also trickle paths where water draining vegetated areas flows over the rock, which continues for prolonged periods after precipitation has ceased. This phenomenon usually gives rise to a dark discoloration of the rock.

During the monitoring period, until 1995, a shelter covered a large part of the site Tanum 12. It was built in order to protect the rock carvings from weathering. The effect of the shelter was, however, doubtful. Trickle water could still flow across the outcrop and organic material could as well reach the area. There was also a risk that conditions under the roof during certain weather conditions could become moister than in the open air. Neither was it possible to observe that the rock breakdown decreased. In 1996 the shelter was dismounted, and the area is now temporarily covered during the winter season, when there are few visitors. This probably minimises the risk for frost weathering. Furthermore a dike was built above the rock carvings preventing drainage water from vegetated areas to trickle over the rock.

Repeated measurements were performed at five occasions at Tanum 12 (Aspeberget I), in the shelter area, of a quadrangle comprising the back of a deer and the lower part of a ship. They were made in September 1994, September 1995, August 1996, August 1999 and in September 2002. The slope is here 22º towards NNE. The downwearing rate was calculated to 1.12 mm per 1000 years for the entire period between 1994 and 2002 (figure 20). Between 1995 and 2002 the rate was 0.84 mm per 1000 years, for the period from 1996 to 2002 it was 0.02 mm per 1000 years, while the denudation rate between 1999 and 2002 was calculated to 0.23 mm per 1000 years. This means that almost all detected material loss at this site occurred before 1996, and that denudation rates were much quicker during the first two years of the monitoring period. Since there are no larger abrupt edges or joints in the measurement area, which can disturb the accuracy of the laser scans, the

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calculated figures can be accepted with certainty. One disturbing factor altering the micro relief is, however, flaking of the red paint and new paintings of the rock carving figures.

The process of the ‘micro exfoliation’ could be studied in great detail at Tanum 12 (Aspeberget I). The tiny fragments first seem to increase slightly in volume and are thereby bent upwards. Volume increases of this reason between 1994 and 1995 are shown in figure 21. Within a relatively short time thereafter they collapse, small scars are created from where the rock fragments have been lost, and a surface lowering will be detected by laser scanning. The roughness statistics from Tanum 12(I), seen in table 3 & 4, is fairly similar to this from Skee 619 (Jörlov). Mean and median values are just slightly lower, indicating that the same processes are acting but that the deterioration maybe is slightly less severe at Aspeberget than at Jörlov.

Figure 20. Downwearing to depths of more than 0.5 mm between 1994 and 2002 at Tanum 12

(Aspeberget I). The contour interval is 0.25 mm. Almost all the material loss occurred during the first two

years of the monitoring period. Those areas where ‘micro exfoliation’ was detected between 1995 and

1996 are indicated in the figure. The rest of the deterioration took place before that. The fairly shallow

material loss in the upper right part of the image is due to flaking of the red paint from a rock-carving

figure.

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Repeated measurements were made at two other places just a few meters apart from the previous site, also in the shelter area. At these two places rock carvings are not present and they are not affected by trickling water. Micro maps at Tanum 12(II) were made in August 1996, August 1999 and in September 2002. At Tanum 12(III) laser scans were only made at the two latter occasions. The surface lowering rate is negligible at both measurement quadrangles between 1999 and 2002 and only amounts to 0.03 mm per 1000 years for the period from 1996 to 2002 at Tanum 12(II). On an overlay of micro maps from these two years less than ten very small spots, a few mm in size, with material losses are seen. They are probably due to detachment of a limited number of single mineral grains from the granite. The roughness statistics for Tanum 12(II) and Tanum 12(III) in table 3 & 4 are similar to those of the other investigated granite sites in Bohuslän where there are distinct signs of alteration. At these places the unevenness of the surfaces has been created mainly by varying resistance towards weathering of the different mineral grains in a medium-grained or coarse-grained rock. The distribution of roughness indexes at Tanum 12(II) are seen in figure 22.

Figure 21. Volume increases to heights of more than 0.4 mm at Tanum 12(I) between 1995 and 1996.

The spot at the bottom, to the left, can easily be identified as an area with material loss in figure 20. The

uplifting of tiny rock fragments is a precursor to their removal.

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During 1992 a laser scanning was made in the shelter area, with the prototype device, of a bull figure immediately next to the measurement quadrangle Tanum 12(I). In 1993 another part of this bull figure was micro mapped. The weathering degree and phenomena are essentially the same here as on the other investigated parts in the shelter area at Aspeberget. Details on digital images made from the measurement data also display great similarities. Roughness statistics are shown in table 5. It seems that the indexes generally are lower than those obtained from later measurements, especially the mean and median values from 1992. The reason can be that a large part of the micro map was made over painted areas of the bull figure. The paint creates a much smoother surface than the original. It should also be remembered that necessary recalculations of data collected with the prototype equipment induces a smoothing of the original data giving somewhat lower roughness indexes than they ought to be.

Figure 22. Distribution of roughness values from the site Tanum 12(II) at Aspeberget, based on

calculations from squares sized 10x10 mm with one height recording on every square mm. The

example is typical for investigated granites where there is a distinct micro relief due to varying

resistances towards weathering by different minerals in the rock. The roughness indexes nearly forms a

normal distribution, indicating that rock characteristics are similar over the entire surface.

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In 1993 another micro mapping at Tanum 12 was made with the prototype equipment. It took place outside the shelter area over a figure of a circle-cross where the slope is 12º towards N. The rock surfaces are here somewhat better preserved than at the other measured places at Tanum 12. Micro glacial striations are still visible on some of the potassium feldspars. There is, however, an easily observable differential weathering between the varying minerals in the granite. This type of deterioration is more evident on the right part of the circle-cross than on the left part. These observations are evidenced by the roughness statistics (table 5 & 6), showing fairly low mean and median values. When the roughness indexes are viewed in more detail it can be seen that they indicate very smooth surfaces to the left in the measured area, while indexes to the right are similar to those from the other Tanum 12 laser scans. The micro topography created by the differential weathering is thus clearly depicted by the roughness calculations. Since the characteristics of the measurement area varies the skewness and especially the kurtosis become high.

Important parts of the rock carving field at Tanum 12 (Aspeberget) are intensely weathered and rock breakdown has already gone far. The future for many groups of figures is therefore not very bright. It might, however, be possible to delay the inevitably downwearing that ultimately leads to disappearance of the rock carvings. Any significant downwearing could, for example, not be detected after 1996. Then the shelter was dismounted, drainage water was stopped from trickling over the surface and temporary covering of the area was made every winter. This can imply that the precautions were successful. That hardly any material loss was detected after 1996 is, however, no proof that downwearing rates have slowed down. Small rock fragments are still observed to disappear from the rock even if it not has happened from the micro mapped areas after 1996. It is necessary to remember that rock breakdown rates are highly variable both in time and spatially.

5.7.7. Tanum 18 (Aspeberget, ship), j

In 1993 a laser scanning, with the prototype device, was made of a ship figure at Tanum 18. This place is also on Aspeberget and the slope of the rock at the ship is 14º towards E. Other figures here are, for example, humans with spears, animals and different types of spirals. The weathering is intense and the most common type of damage is due to the ‘micro exfoliation’ that also was observed at other places on Aspeberget and at one of the investigated sites in the parish of Skee. The tiny exfoliated sheets can without effort be crushed by hand. The surface of the rock has often a brownish discoloration and granular disintegration is seen almost everywhere. The upper few mm of the rock is soft due to alteration processes and can easily be destructed.

The contours of the ship are fairly difficult to follow on a micro map produced from the laser scan data since weathering already partly has destroyed the figure. Roughness data are seen in table 5 & 6. They indicate that the surface is slightly smoother than at the other intensely deteriorated surfaces on Aspeberget despite that rock characteristics are similar. The reason might be shallower depths of the carving or slightly smaller grain sizes of the granite at Tanum 18 than at Tanum 12.

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By analyses of the observations and the micro mapping results it can be concluded that the site when the measurements were made was in a state of rapid decay. This means that the rock carvings under open air conditions would become more or less completely destructed in a relatively short time span, maybe a few tenths of years. A more or less permanent covering is now made at the site. This might be a good conservation measure provided that it is thick enough to prevent soil forming processes to reach down to the rock surface.

5.7.8. Tanum 26 (Aspeberget, horse), k

The rock at Tanum 26 looks in contrary to the other investigated places on Aspeberget very fresh. Micro glacial striations are present next to the carvings and signs of weathering are limited. Some mineral grains have been lost from the granite and slight brownish discoloration is occasionally seen. Lichen growth was when the investigations were made also almost absent. It is obvious that downwearing rates have been very low at this locality during the Holocene.

Figure 23. Digital shadow image of a part of a well-preserved rock carving of a horse figure at Tanum

26 (Aspeberget). The imaginary light comes from NE.

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Part of a horse figure, where the rock has an inclination of 17º towards E, was measured with the prototype laser scanner in 1993. The rock carving is in a very good condition and a digital shadow image of it is found in figure 23. The glacial micro striations are not seen in the image since the measurement resolution in the x- and y-directions were too coarse to reproduce them. The depth of the carving is seldom more than about two mm. Cut marks indicating how the horse figure was made can still be observed. The roughness data in table 5 & 6 show that the site, together with Massleberg in the parish of Skee, is among the smoothest of all measured rock carving areas. Laser scanning has also been performed, for other purposes within the ESPED project, at the coast on Ramsvikslandet about 30 km S of Tanum. The measured sites in the granite here lie only a few m above the present sea level, meaning that they have been exposed to open air conditions for less than 1000 years because of the land rise. Even when compared to Ramsvikslandet it comes out that minimum and mean indexes at the horse carving at Tanum 26 and at the carvings at Skee 614 are lower. They correspond maybe to an exposure to air of only a few 100 years.

It can be stated that the good condition of the horse carving will persist for a long time unless environmental conditions are altered severely in a bad direction. As long as surfaces still are smooth the area for attack by weathering agencies is limited. When, however, slow initial downwearing rates have created a more irregular surface it can be expected that also the speed of weathering will increase. It is difficult to explain why some rock carvings are almost unaltered while others are heavily damaged. One explanation can be slight differences in rock properties influencing the susceptibility to breakdown. Another factor is for how long period the carvings have been exposed. We usually do not know if a site has been covered by, for example, thick protecting soil layers for long periods after they were carved. Another reason for heavily damaged areas can be anthropogenic influence. Lichens might have been removed and cleaning been done with improper methods in the past.

5.7.9. Tanum 255 (Fossum), Nr 17

The frequently visited rock-carving field at Fossum lies about 3 km E of the Tanum church, next to a road. The outcrop measures about 15x3 m. The most common types of figures are warriors and ships. ‘Original’ surfaces with micro glacial striations are present on some feldspar crystals. Minor fragments at their edges are, however, easily detachable. Furthermore parts of the granite have attained brownish colours, which can indicate an initial weathering.

The micro mappings were made at a slightly arched part of the rock where the slope is between 8º and 14º towards ESE. To the right in the measured area is a man with an axe, and to the left parts of a circle-cross. The laser scans were performed in September 1994, July 1996, August 1998 and in April 2003. Computations of material losses to depths of more than 0.5 mm give very low denudation rates, varying between 0.01 and 0.03 mm per 1000 years for the different calculation periods. When overlays of micro maps are studied it is seen that the downwearing has affected several areas, but always only to a very limited amount. In figure 24 the denudation to depths of more than 0.3 mm can be seen. Changes are visible at about 30 places, and a volume of 27 mm3 has disappeared from a total area of 377 mm2. A calculation from these data does still indicate slow deterioration rates,

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0.08 mm per 1000 years. The roughness data in table 3 & 4 only show very slightly lower indexes than at the sites on, for example, Aspeberget that are in a worse condition. There has, however, been created a fairly pronounced micro relief because of the contrast between ‘original’ surfaces and places where mineral grains are lost.

Figure 24. Material losses to depths of more than 0.3 mm between 1998 and 2003 at Fossum in the

parish of Tanum. The contour interval is 0.2 mm. A limited breakdown has taken place at about 30

minor areas.

It can be concluded that weathering is presently taking place at Fossum although the rate is low. It mainly occurs by granular disintegration, where single mineral grains or only parts of them are lost. Most probably the surface lowering rate will not increase dramatically in the near future. The site must, however, be kept under control since there is

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rock breakdown at present. The near proximity to a road and many people walking on the rock carvings, despite that a pavement has been constructed beneath the outcrop, are environmental factors that can influence the course of future weathering negatively.

5.7.10. Tanum 72 (Tegneby, Mellangården), l

The rock carvings at Tegneby, Mellangården lie uphill, in close proximity, to the well- known panel at Litsleby (official Nr 75-76, parish of Tanum). They are only a few mm deep and are surrounded by three small stone-settings. The carvings consist of a group of armed warriors on horses. The warriors are carrying rectangular shields of an Iron Age type. This means that the figures are of a later origin than from the Bronze Age (Bertilsson, 1987), and of this reason can not have suffered weathering as long as carvings at other places. The potassium feldspars in the granite form an even upper surface in the micro relief, while the micas often are gone. The slope of the outcrop is only 4º degrees towards NE and glacial striations are also seen in this direction.

Measurements were made already in 1992 with the prototype laser scanner. Mean and median roughness indexes are comparable to those of the circle-cross at Aspeberget 12 (table 5), but the skewness and the kurtosis values are much lower. This means that there are no remarkable spatial differences on the micro mapped area at Tegneby-Litsleby. When images, made from the laser scanner data, are viewed in detail it can, however, be seen that the painted figures are smoother than natural rock areas. The thickness of the paint obviously hides minor irregularities.

Observations at the site indicate that the rock-carving panel is in a fairly good state and not at great risk in the near future. It also seems that anthropogenic abrasion caused by vehicles on a formal drive across the figures not have influenced them too significantly. Some artificial smoothing can maybe be observed. There are, however, signs of mineral weathering that already have created a somewhat more distinct micro relief compared to the best preserved investigated sites in the Bohus granite at Skee 614 and Tanum 26.

5.7.11. Tanum 417 (Kalleby, Västergården), m

The investigated site at Kalleby lies just to the E behind an outbuilding of the farm Västergården on an outcrop that slopes 15º towards E. The figures were difficult to recognise when the investigation was made because of a dense lichen cover. There are some minor ‘original’ surfaces, where micro glacial striations still can be observed, but signs of continuing rock breakdown are common. Mineral weathering and granular disintegration creating small hollows in the rock are seen almost everywhere. Damage due to flaking is also observed at several places.

The micro mapping took place in 1993 and was made with the prototype laser scanner. Roughness data are as seen in table 5 & 6 similar those from other severely deteriorated sites at, for example, Jörlov in Skee and at Aspeberget. The high mean values means that a pronounced micro relief has been created over the entire micro mapped surface. Since the area already is intensely weathered there is a great risk that the future lifetime of the figures at and near the measured site will be short.

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5.8. Västra Götalands län, province of Dalsland In Dalsland repeated micro mappings have been made at two sites and a single

measurement at one additional site. All investigated places lie at Högsbyn in the parish of Tisselskog in arable land near the shores of the lake Råvarpen. This is the richest rock carving area in the province and according to Rex-Svensson (1982) there are 34 known outcrops with carvings. The bedrock belongs to the Dalsland group that is a mainly sedimentary sequence of nearly 2000 m thickness (Lundqvist, 1979). Dating with the Rb-Sr method indicates that the sedimentation took place between 1080 and 1030x106 years ago. At the measured rock carvings a marly clay slate predominates. White mica (sericite) is the most common mineral, but quartz and calcite are also present. By deformations the clay slate has often been altered to a slightly folded phyllite (Samuelsson, 1982).

5.8.1. Tisselskog 11 (Högsbyn, the meadow), Nr 18

The area lies in a park-like environment just south of a few buildings. Here are several outcrops, with rock carvings, rising about a m or less above the surrounding grassland. They are all elongated in N-S, which also is the strike direction of the clay slate. There are several damaged areas in the form of cracks and of scars where cuneiform fragments have been lost from the rock. The sizes of these fragments were often at least a few cm. There is on most surfaces also a dense lichen cover.

Micro maps were made in September 1995, August 1997, September 1999 and in July 2002 on the E facing part of an outcrop that was given the number 23 by Rex-Svensson (1982). It is difficult to interpret what the measured figure represents. There are wedge-shaped scars immediately nest to the laser scanned figure. Calculations of material losses to depths of more than 0.5 mm give for the period between 1995 and 1997 a low denudation rate, 0.13 mm per 1000 years. From 1999 to 2002, however, the computed rate was 1.56 mm per 1000 years. When the height contours on micro maps were viewed in more detail it could be concluded that nearly no downwearing had occurred. The entire indicated material loss was at a sharp edge, and with a laser scanner of the triangulation type parallax errors can easily result on such places if the positioning of the measurement device has not been exactly similar when consecutive micro mappings were made. It can be seen in the roughness statistics especially in table 3, but also in table 4, that the minimum and 1:st quartile indexes are very low. They are typical for the smooth structure a very fine-grained rock often attains. In such rock types this structure can persist although surfaces have been weathered. The maximum indexes are high and are due to the sharp edges of the weathering scars within the measurement area.

During the seven year long monitoring period no remarkable material loss has taken place from the investigated site. With the laser scanner only downwearing on the micro scale is studied. Rock breakdown on the meso and macro scale that might take place in the vicinity is not detected. It seems that there in the future also will be limited deterioration on the micro scale and that the figures will continue to be well preserved. There is, however, at this place a much greater risk that larger rock fragments will be lost causing destruction of large part of the figures instantly.

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5.8.2. Tisselskog 15 (Högsbyn, Ronarudden), Nr 19

Ronarudden is a small peninsula stretching out into the lake Råvarpen. On its outermost part there are numerous rock carvings at an altitude of only about one m above the mean water level of the lake. The area is reproduced in figure 25. The panel is divided in three parts by major joints. The clay slate strikes in the direction 10º and its dip is 36º towards W. There are distinct structural surfaces in the dip direction. Several small hollows, with a size of a few mm, are present on the outcrop both within the rock carving figures and outside them. The hollows resemble the weathering phenomena ‘pitting’, but it is unsettled how they have been created. As at Tisselskog 11 several cm big wedge-shaped fragments can weather away from the rock. Several damaged parts caused by this process are seen. It is, however, difficult to assess their age. Lichens are present and they might cause breakdown by detachment of minor rock fragments from the surface of the clay slate.

Figure 25. Photo of the rock-carving site at the outermost point of the small peninsula Ronarudden in

the parish of Tisselskog. The jointed structure of the clay slate is obvious at this place.

The micro mapped area, where the slope is 24º towards ESE, contains a foot-sole figure and parts of another foot-sole. The measurements were made in September 1995, August 1997 and in July 2002. Calculated downwearing rates are less than 0.01 mm per 1000 years for the entire seven-year period while it is 0.30 mm per 1000 years between 1997 and 2002.

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Careful examinations of contour maps, produced from the laser scanning data, however, show that the downwearing during the last five years of the monitoring period also has been negligible. The roughness data in table 3 & 4 show similar characteristics as at the other site in clay slate, Tisselskog 11. The most remarkable difference is the much higher maximum value at Ronarudden. The reason is that edges towards parts where wedge-shaped fragments have been removed are more prominent here. The great difference between very smooth surfaces of the fine-grained clay slate and the abrupt height variations within the measured area leads to a very high standard deviation of the roughness indexes and also to high skewness and kurtosis values.

The present state of the rock carvings at Ronarudden is maybe somewhat better than of the rock carvings in the meadow area at Högsbyn about 300 m to the N. Future risk for the area is, however, similar. There will only be very limited changes on the micro scale as evidenced by the laser scanning investigations. Also here losses of larger cuneiform fragments, due to weathering processes, are likely to cause much more severe damage. It is, however, very difficult to say when this possibly might happen since such removal occurs as a sporadic event.

Figure 26. Digital shadow image of a foot-sole at Högsbyn in the parish of Tisselskog, site n. The

imaginary light comes from NW. The engraved contour and still preserved cut marks within the foot-sole

are seen in the image.

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5.8.3. Tisselskog 12 (Högsbyn, foot-sole), n

Approximately at half distance between the investigated rock carvings at Ronarudden and the meadow area at Högsbyn there is an outcrop where fourteen foot-soles are found on its N end. It can be seen that the contours around the feet are engraved while interior parts are hammered and cut out (Andersson, 1997). The engraving by a piece of flint or maybe a bronze knife has been possible since the clay slate is softer than the rock at most other rock carving areas. The surfaces on this part of the outcrop look to be in a fairly good state and no major damaged areas are observed, except a joint between some of the figures. The lichen cover is, however, generally dense.

A single micro mapping, of the area seen in figure 26, was made in September 1995. The slope is here 16º towards N. Roughness statistics are reproduced in table 5. Mean and 1:st quartile indexes are similar to those of the other two sites at Högsbyn, but since abrupt edges towards damaged areas are lacking mean and maximum indexes are considerably lower. The micro relief created by the cut marks within the foot-sole is, however, clearly depicted by the roughness calculations.

There seems not to be any immediate danger for meso-scale damage by losses of wedge-shaped rock fragments near the foot-soles, except for the area next to the joint. Probably the risk for destruction in the near future is lower than at the other two investigated clay slate localities. The state of the rock on a micro-scale also looks good. Minor rock fragments might, however, be detached together with the red paint when it flakes away. The paint has been used in order for tourists and the public to be able to study the rock carvings easier. Lichens might as well be able to remove minor rock fragments.

5.9. Västra Götalands län, province of Västergötland Repeated micro mappings in the province of Västergötland have been performed at one

site in Lower Cambrian Lingulide sandstone near the foot of the mesa mountain Kinnekulle. Furthermore one single measurement was made a few m away from this site. The Lingulide sandstone forms the upper and most important part of the sandstone layers at Kinnekulle. It is fairly uniform and the beds can attain a thickness of almost one m (Johansson et al., 1943). The beds are separated by thin lamella of shale. The sandstone is fine-grained, fairly soft and the colour on fresh surfaces is white with a slight tint of grey or yellow. It contains about 97% SiO2 and minor amounts of pyrite are usually present in the form of small cubical crystals. The Lingulide sandstone has in the past been used extensively as a building stone and many medieval churches around Kinnekulle are, for example, made of it.

5.9.1. Husaby 70 (Flyhov), Nr 14 & f

The outcrop with rock carvings at Flyhov, in the parish of Husaby, is almost flat and has a size of several 100 square meters. The rock art was discovered in 1889. Among the figures are ships, wheels, foot-soles and humans. A few tenths of years ago the soil next to the rock carvings was removed. This ‘new’ area does not contain as many figures as the ‘old’ one, but excellent opportunities are given to study microforms caused by glacial

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erosion. The glacial striations are almost perfect since the surface only has been exposed to weathering for a limited time. There are also very well preserved crescentic fractures and crescentic gouges. On other parts of the outcrop plastic sculpture caused by glacial melt water are seen. The areas that have been exposed for a longer time are lacking the finer striations. A yellowish brown discoloration, probably due to alteration of the pyrite, is found at many places, indicating an ongoing weathering. The lichen growth is extensive and they are firmly attached to the surface of the very porous sandstone, and therefore usually difficult to remove.

Figure 27. Surface lowering to depth of more than 0.5 mm between 1994 and 2003 at Flyhov in the

parish of Husaby, province of Västergötland. The contour interval is 0.25 mm. The figure indicates that

the deterioration has been disastrous during the monitoring period. It is, however, difficult to assess

whether all calculated surface lowering is due to losses of grains from the sandstone or if the measured

volume changes are caused by other, more temporal, variations of this soft and porous rock.

Repeated measurements were made at five occasions at a site sloping 5º towards E, in September 1994, August 1996, July 1997, August 1998 and in April 2003. To the left in the measured area there are two fairly deep but diffuse figures that might be foot-soles and to the right there is a ship. Between the figures a clearly visible crack is present. Calculation

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of the downwearing during the entire monitoring period of nine years yields the disastrous downwearing rate of 60.83 mm per 1000 years (figure 27). This means that the surface, on an average, has been lowered by more than 0.5 mm during nine years only. Similar and also much higher rates have, however, been achieved from other areas with less durable rocks as, for example, chalk at the coast in Sussex, England (Swantesson et al., 2006a). For periods after 1996 calculated downwearing rates are still high but not at all that extreme. The rates vary between 2.46 and 3.23 mm per 1000 years. The surface lowering between 1997 and 2003 is shown in figure 28. From the laser scans it appear that most of the downwearing happened before 1996, that it slowed down between 1996 and 1998 and that rates became somewhat faster again after 1998.

Figure 28. Surface lowering to depth of more than 0.5 mm between 1997 and 2003 at Flyhov in the

parish of Husaby, province of Västergötland. The contour interval is 0.25 mm. Downwearing is detected

over large areas, but never to great depths.

It is remarkable that the indicated surface lowering has occurred over extensive areas but seldom to depths of more than one mm. Larger rock fragments that have disappeared from the rock have in no cases been detected from overlays of micro maps from the different measurement occasions. It seems that the fine quartz grains of the rock are lost

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successively and at almost similar rates over the entire surface. The roughness statistics in table 3 & 4 show generally low indexes indicating that the rock surfaces are smooth despite that weathering obviously has occurred. The reason is that breakdown proceeds in a different way in a rock composed of only one dominating mineral compared to, for example, granite. There are no hollows and sharp edges that are created by varying susceptibility towards weathering by different minerals.

A single laser scan was made in September 1994 of a circle-cross on the fairly recently cleansed part of the outcrop where glacial microforms still are present. The figure is shallow, but very well preserved (figure 29). Cut marks showing how the circle-cross was made are clearly visible. The roughness data, in table 5 & 6, does not differ very much from those of the much more weathered area where repeated micro mappings were made. This kind of statistics gives in crystalline rocks as granites excellent indications of how far rock breakdown has gone. In the Lingulide sandstone, however, the micro relief does not seem to increase with time of exposure to weathering.

Figure 29. 3-D model in orthographic projection of a well preserved circle-cross in Cambrian sandstone

at Flyhov in the parish of Husaby, province of Västergötland. The vertical exaggeration is 2.5 times.

It is difficult to explain the extreme downwearing rate that was calculated for the period between 1994 and 1996 at Flyhov. There are no grounds to believe that is was caused by errors of the laser scanning device or by inexact replacements of the frame of the equipment. Abrupt edges that at other places can produce parallax errors when micro maps are overlain, if the frame has not been placed identically at consecutive measurement, are almost absent in the sandstone. Other reasons for the indicated volume loss must therefore

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be sought. One possibility is that the lichen cover on the measured surface varied considerably between the measurement occasions since it was difficult to remove completely. The properties of the Lingulide sandstone are very different from the Precambrian rocks at other investigated sites. It has, for example, a very high porosity of about 11%. This figure was achieved by weighing a sample before and after having soaked it in water under a weak vacuum of approximately 100 hPa (Swantesson, 1989). Volume changes can occur in porous rocks due to varying water contents. Prick (1999), for example, reviews literature and describe own experiments where she has measured the lengthening due to high water contents of samples from other porous rocks. She mainly used limestones, but this predominantly physical process might be applicable for sandstone as well. This means that if the measurements have been made under too varying moisture and temperature conditions the consequence can be misleading results. Further, but more unlikely, reasons for the calculated volume decrease can be minor displacements of the sandstone beds or slight height movements of the minor studs used as fix marks. Such movements have, however, not been observed at any of the other laser scanned surfaces in southern and central Sweden.

Despite that environmental factors can have induced some misleading results it can be concluded that present downwearing rates in the Lingulide sandstone at Flyhov are very high. Most probably the deterioration will continue at a similar speed also in the future. The contrast between different parts of the rock carving field according to how long the exposure has been is easily observed. This is also an evidence of rapid weathering rates. In frost weathering experiments Lingulide sandstone broke down about 40 times faster than Bohus granite (Swantesson, 1989). Laboratory simulation studies thus also points to that the rock at Flyhov will disintegrate considerably faster than the rocks at most of the other investigated sites.

5.10. Östergötlands län Repeated micro mappings have been made at five places in the county of Östergötland

and single measurements at five additional places. All sites except Hästholmen in the parish of Västra Tollstad are situated in the town Norrköping or its vicinity. Hästholmen lies only a few 100 m away from the shores of Lake Vättern, about 35 km S of the town Motala. According to Dahlman & Persson (1981), the bedrock here consists of postorogenic acid, porphyritic volcanic rock, where phenocrysts comprise more than one third of the rock volume.

The localities in the parish of Östra Eneby in the Norrköping area lies on supracrustal Svecofennian rocks where mica schist dominates (Kornfält, 1975). The origin of the mica schist is clayey sediments and its colour is dark grey. There is usually some folding. Sometimes up to five cm big andalusite crystals are present. These crystals often protrude from the rest of the rock in the present micro relief since they have a great resistance towards weathering and erosion. The mica schist is banded with a greyish blue, fine-grained plagioclase quartzite having layers with a thickness of between one and six dm. The commonly seen shifting between the dark and the light bands is a sign of the original sedimentation processes. The site in the parish of St. Johannes is situated on metaargillite

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that can be described as biotite-rich veined gneiss, (Kornfält, 1975). This rock is more intensely metamorphosed than the mica schist. Characteristic minerals are sillimanite, biotite, potassium feldspar, muscovite and plagioclase. The measured rock carving in the parish of Borg lie on late kinematic medium- to fine-grained granite with a colour varying between grey and greyish white (Kornfält, 1975). Pegmatite and aplite veins are fairly common.

5.10.1. Borg 51 (Herrebro), Nr 20

The 3.5 m high outcrop lies as seen in figure 30 only about twenty m away from a motorway. It is surrounded by grassland where beef cattle are grazing, and it is fairly difficult to access for the public. There is no obvious damage in the vicinity of the rock carvings. Single mineral grains are neither seen to depart from the granite. Some fine mineral dust is, however, present on the rock surfaces. Varying hardness between different parts of the rock might later give rise to differential weathering. The lichen cover was limited at the time for the first two measurements, but it had become extensive when the last micro mapping should be made. The lichens were very firmly attached to the rock and it was impossible to remove them completely with only water and a soft brush.

Measurements were made of a shallow network figure in September 1994, July 1996 and in August 2002. The site faces the motorway and slopes 12 towards SW. Between 1994 a downwearing rate of 0.93 mm per 1000 years was calculated. Most of the breakdown was detected in the upper right quadrant of the micro mapped area. After 1996 no further surface lowering was detected. The reason is probably the intense lichen growth, where they during the last measurement in spite of cleaning partly remained especially in that area where most of the downwearing was detected. The lichens were thus hiding previously deteriorated areas. Roughness statistics in table 3 & 4 show that minimum, mean and 1:st quartile indexes in almost all cases are lower than for other granites in, for example, the province of Bohuslän. It can not generally be said that the results show that the weathering degree is lower at Herrebro. Most likely the reason for lower values is a different microstructure and a finer grain size of the rock.

Material losses have been detected but indicated rates can not be considered disastrous. The site at Herrebro is, however, at great risk, mainly due to salt weathering. When the motorway next to it is salted during winters, to prevent slipperiness, salt spray is spread over the outcrop when vehicles pass at high speeds. Other pollution from the traffic might also influence the state of the rock. Salt weathering has among earth scientists since long been regarded important. Laboratory simulation experiments by, for example, Kwaad (1970) & Goudie et al. (1970) show that most salts are very effective in causing rock breakdown. This is also the case for a non-hygroscopic salt as NaCl that is used on the roads. According to Swantesson (1989) even small amounts of salt can cause rapid and severe rock breakdown of Swedish Precambrian rock provided that wet and dry conditions alternate. An explanation why larger amounts of breakdown not were indicated by the laser scanning could be that the motorway was constructed as late as in 1994.

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Figure 30. Photo taken from the micro mapped area at Herrebro in the parish of Borg. The close

proximity to a motorway causes salt spray on the outcrop when vehicles are passing during the winter

when the road is salted.

5.10.2. St. Johannes 14 (Egna hem), Nr 21

St. Johannes 14 lies within a built up area with mainly three to six storey houses. Despite its location the site does not seem to attract many visitors, but fragments of glass are seen on the outcrop. Certain parts of the area show substantial damage and holes from the posts of a formal fence have left ugly scars. Some mineral grains that have been lost from the gneiss are present but no serious recent weathering can be observed with the naked eye. There is, however, a relatively dense lichen cover on the entire outcrop.

The measurements were made of a circle-cross with three cup marks inside it in September 1994, July 1996 and in August 2002. The slope of the rock is 10º towards NNE at this place. There is a damage of more than ten cm in the left part of the circle-cross. It is difficult to deduce how this damage was created. It might be anthropogenic. Calculated downwearing rates for the period from 1994 to 2002 and for the period from 1996 to 2002 were almost identical. They varied from 0.22 to 0.25 mm per 1000 years. The spatial distribution of the rock breakdown within the measurement quadrangle is seen in figure 31. Overlays of micro maps for both calculation periods give almost similar images. Roughness data in table 3 & 4 show that the micro topography neither can be considered as especially smooth nor is it very rough. The site can be considered to take a medium position among the measured places in this context.

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No further breakdown has been indicated in, or at the edges of, the already present damaged part of the rock carving. At other areas material losses could be detected with certainty, but amounts were small. It thus seems that the rock carving at the moment is fairly stable and that it will remain so in the near future.

Figure 31. Material losses to depths of more than 0.5 mm at Egna hem in the parish of St. Johannes

between 1994 and 2002. An image for the period from 1996 to 2002 shows an almost identical spatial

distribution of breakdown.

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5.10.3. Västra Tollstad 21 (Hästholmen), Nr 22

The rock-carving field at Hästholmen, near to Lake Vättern, lies on an almost flat outcrop only slightly higher in altitude than the surrounding arable land. There is grass vegetation in joints and in minor depressions of the rock. The general appearance of the rock surfaces indicates that they usually are in a good state, but damage probably caused by flaking is fairly common. There is also often a dark, almost black, discoloration. Furthermore anthropogenic damage caused by the posts from previous fences is seen.

Micro mappings were made in August 1995, September 1997 and in June 2002. The figure at the measured area is a fairly diffuse ship with a simple outline, lying in a shallow rock pool. This minor depression is temporarily filled with water. In the middle of the measurement quadrangle there are still remnants of an iron post from an old fence. The carving can thus be considered as already destroyed. In the lower right corner of the micro mapped area flaking has apparently taken place. The calculated downwearing rate between 1994 and 2002 is low, only 0.07 mm per 1000 years. For the period from 1996 to 2002 no surface lowering to depths of more than 0.5 mm could be detected. The indicated material loss took place along the edges of the area where flaking had occurred. The roughness data in table 3 & 4 indicate that the surfaces of this porphyritic volcanic rock are very smooth. Abnormal height values were recorded near the remnants of the iron pole by the laser scanner equipment due to reflections. The 10x10 mm or 20x20 mm large squares used for the calculation of roughness indexes from areas near the pole were of this reason not included in the roughness statistics presented in the two tables.

There is only very limited recent downwearing at the already anthropogenic severely destroyed investigated rock carving at Hästholmen in the parish of Västra Tollstad. Breakdown at the edges of probably exfoliated areas does not seem to be especially active at this place. At Hästholmen it is difficult to without doubt determine whether the observed flaking is due to natural rock decay or if the damaged areas are caused by fire. Sometimes almost similar scars can be created by both these processes. The further deterioration in the near future will presumably continue to be limited.

5.10.4. Östra Eneby 1 (Himmelstalund), Nr 23 & o

In the Himmelstalund Park there are about 50 rock carving panels with together more than 1500 figures. The area with rock art lies a few meters higher in altitude than the surrounding grassland and contains several fairly flat outcrops. There are at most places no obvious signs that rock breakdown has gone very far and glacial striations are generally distinct. Some damage that can be expected to be due to anthropogenic abrasion is, however, seen where a cycle track crosses a number of rock carvings.

Repeated measurements where made at five occasions in September 1994, July 1996, July 1998, July 2000 and in July 2002 of a ship figure about 100 m NW of the main rock carving field. The slope is here 8º towards SSW. Water sometimes trickles especially over the right part of the ship within the measured area. This has caused a brownish discoloration of the rock surface. The lichen cover is usually rich, but it is absent from certain parts of the rock that are lighter in colour. Main structures of the figure follow the same direction as the glacial striations. They have thus been used as an aid when the rock

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carving was made. The downwearing to depths of more than 0.5 mm for the entire eight-year period is reproduced in figure 32. During this period the calculated rate was 0.09 mm per 1000 years. An overlay of micro maps from 1996 and 2002, when the computed rate was 0.21 mm per 1000 years, looks almost identical. This means that hardly any material losses had occurred between 1994 and 1996. For the period from 1998 to 2002 calculations reveals a downwearing rate of 0.17 mm per 1000 years, and overlays of micro maps indicate that fewer areas are affected. During the last two-year period only a few minor areas with material losses are indicated on overlays of micro maps and the rate is only 0.06 mm per 1000 years. Most of the fairly limited but clearly detected breakdown within the measurement quadrangle thus took place between 1996 and 2000. The roughness statistics, shown in table 3 & 4, have low minimum and 1:st quartile indexes indicating the generally smooth structure of the fine-grained mica schist. Some squares, over which the calculations were made, however, display much higher indexes. Here small hollows that can be described as the weathering phenomena pitting are present. This phenomenon also results in high skewness and kurtosis values.

Figure 32. Downwearing to depths of more than 0.5 mm at the investigated site at Himmelstalund in the

parish of Östra Eneby in the town Norrköping between 1994 and 2002.

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At two further places, within the main rock carving area, at Himmelstalund single micro maps were made in August 1995. One was performed of a dog-like animal, and is part of a hunting scene for wild boars. This scene is also the logo of the Bronze Age Society in Norrköping. The carving lies in a shallow runnel that once was formed by glacial melt water. Within the other measurement quadrangle there is a ship figure. Here the slope of the rock surface is 9º towards NE. As at the place where repeated laser scans were made the ship is cut in the same direction as the glacial striations. The figure does not consist of simple contours. Its entire interior is carved out. The minimum roughness indexes for both measured areas are low (table 5) depicting the smooth surfaces of the mica schist. Median and 1:st quartile indexes for the ship are higher than for the animal figure since large parts of the measurement was made of the worked areas of the ship’s interior. The cutting created a somewhat more pronounced micro relief than the natural glacially polished rock surface where almost all height differences are due to glacial striations and thus very small. A joint within the measurement quadrangle causes a higher maximum index and also higher standard deviation, skewness and kurtosis of the animal figure than of the ship.

The laser scan site at Himmelstalund can be considered fairly stable at present, but small changes were evidenced. There is no reason to believe that downwearing rates will increase dramatically in the near future. The area is very easily accessible and many people cross the area by foot, bicycle or by moped without a primary aim of studying the rock carvings. If footpaths and cycle tracks were diverted it might help to preserve the valuable rock carvings for as long as possible by minimising anthropogenic abrasion.

5. 10.5. Östra Eneby 8 (Fiskeby), Nr 24 & p

The rock carvings at Fiskeby lie near the entrance of an industry, with the same name, and next to a parking area. The site was described in the nineteenth century but have since then been covered by industrial waste until a few tenths of years ago. Of this reason there are some stains of tar and rust on the rock. The outcrop is fairly flat and partly overgrown by grass vegetation. The carved figures are distinct and well preserved. Hardly any signs of deterioration can be seen with the naked eye on the rock surfaces.

Repeated measurements were made in September 1994, July 1996, July 2000 and in August 2002 of a part of the area shown in figure 33. At this place the rock is somewhat trough-shaped and has a slope of 15º towards E. Water that is collected in the lower part of the trough freezes during winter and there is a risk that this can induce frost weathering. No studs were placed in the rock at this site. The corners of the andalusite crystals were instead used as fix points. This made the procedure of overlapping micro maps made at different occasions less exact than at places where studs were used. Calculations for the period between 1996 and 2002, where the best overlap was achieved, indicate an almost negligible downwearing rate of 0.01 mm per 1000 years. Comparisons with micro maps from 1994 and 2000 also show that virtually no changes have occurred. The roughness statistics in table 3 & 4 verify that the surfaces of the rock are very smooth and little affected by weathering. The protruding andalusite crystals cause a few higher indexes.

In July 1998 single micro mappings were made at two further quadrangles at the same site. They both lack rock carvings. The objective was to see if there were any differences in

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the micro relief between areas that had been covered by waste material and areas that had been exposed to the air continuously at least since the rock carvings were first described. Östra Eneby 8 (I) in table 5 is from the surface from where material has been removed recently, while Östra Eneby 8 (II) is from the surface that has been exposed for a longer time. The exposed surfaces are easy to find since they in contrast to the excavated areas have a dense lichen cover. The roughness statistics from both sites are, however, almost identical. All indexes are similar except that the maximum index at the exposed site is higher, which also leads to higher skewness and kurtosis values. There is in this investigation thus nothing that points to that deterioration has gone further on the exposed surface than at the surface that has been covered for a long period.

Figure 33. Photograph of the micro mapped rock carving at Fiskeby in the parish of Östra Eneby,

Norrköping. The measured area includes the man with a spear in the right part of the ship. The

protruding andalusite crystals are a characteristic of the rock at this place.

The rock carvings at Fiskeby are in a very good state and only negligible material loss could be detected by the repeated laser scans. The only observed changes where due to flaking away of the red paint used in the figures themselves. Most probably the figures will continue to be in an excellent state for a long future period. Despite this a good management of the area is needed to keep the rock carvings, for as long as possible, in such satisfactory conditions.

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5.10.6. Östra Eneby 23 (Ekenberg), q

At Ekenberg there are about 370 figures that usually are deeply carved and in a large format. The outcrop is fairly flat and the lichen cover is usually dense. A micro mapping was made in September 1994 about one m lower in altitude than the crest, where the rock slope is 5º towards SW, of part of a ship figure. There are spiral figures within the ship structure. In the right part of the measurement quadrangle there is a joint. Mineral grains and minor rock fragments could be removed from its edges. The rock surfaces otherwise seem to be stable.

The roughness statistics in table 5 & 6 show minimum and 1:st quartile indexes that are almost similar to those that were calculated from the ship at Himmelstalund. The influence from the joint, with high maximum indexes, is only seen in the statistics based on squares sized 20x20 mm, since this part of the figure was not included when the roughness calculations based on squares sized 10x10 mm were made. The state of the rock can also be said to be similar as at Himmelstalund, meaning that there is no serious danger for a fast breakdown in the near future.

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Chapter 6. Weathering phenomena at the investigated sites When rocks are undergoing downwearing the processes usually manifest themselves by

creating specific features such as a variety of different weathering forms. Initially the results of weathering are not visible for the naked eye, but they can be studied by, for example, investigations of mainly physical rock properties. When the deterioration proceeds there will be changes of the micro topography and material losses occur. Several minor weathering forms will also be created. These phenomena are easily detected by the skilled observer and tell that the examined rock surface is subjected to weathering. Ultimately weathering and erosion will change the entire environment and prominent landscape features can in many cases be created. These large scale features are of importance when the long term landscape evolution is treated, see, for example, Lidmar-Bergström (1995 & 1996) and Johansson et al. (2001). At the Bronze Age rock carving sites naturally only recent minor forms have been examined. The study of denudation rates is, however, a common interest both for those who are doing research about present weathering and for those interested in long term changes.

6.1. Visible signs of deteriorationThe approach for evaluating and documenting rock weathering signs on rock carvings

and other ancient stone monuments belonging to our cultural heritage must be systematic. Fitzner (2004) presents an elaborate model for such research, together with examples. A detailed inspection of minor weathering phenomena on the investigated sites lies, however, beyond the scope of the studies presented in this report. Observed micro forms and possible reasons for the downwearing at each site are described in chapter 5. In this section only a brief account of the most common features is given. It is based on a classification of weathering forms on natural rock surfaces in southern and central Sweden by Swantesson (1992b), see table 7. Swantesson (1989) made a more comprehensive description of recent deterioration phenomena in the same area. In table 7 the typical depths of the encountered forms is indicated. Logically only the forms having a smaller depth are found at the rock carving sites. If weathering had created deeper forms the rock art would have disappeared completely.

6.1.1. Surface coloration

It is common that an initial weathering manifests itself by changes in colour of the rock surface. The phenomenon is general and can usually be observed already after a few tenths of years of exposure of a fresh rock specimen. There are several kinds of surface colorations. Some of them form crusts with a thickness of only a fraction of a mm, while others most probably are due to slight chemical alterations of certain minerals in the rock which then attain a different colour than the original. Although the phenomenon is perceived at many places it is most pronounced in environments having many changes between wet and dry conditions, such as rock pools and trickle paths. Often Bronze Age rock carvings are found at places where water regularly trickles over the outcrops. This

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location might be more vulnerable to downwearing than other places on the bedrock where the conditions are less variable.

Table 7. Classification of weathering forms in crystalline rocks in southern and central Sweden. Please,

note that the scale for the typical depths of the forms is logarithmic. The vertical line in the table roughly

separates forms that can have been produced entirely by Holocene weathering (left part) from older

forms or forms where inherited rock properties are important for the present breakdown (right part).

Simplified from Swantesson (1992b).

Weathering forms Most affected rock Typical depths of the forms (meters) types or environments 10-4 10-3 10-2 0.1 1 10

Surface colorations Rock pools, trickle paths (general) ---------

Mineral weathering General ----------

Pitting Basic rocks ------------

Flaking Massive rocks ----------

Rough surfaces Gneisses --------

Differential weathering

acid veins Quartz, pegmatites ---------------

minor basic dykes Amphibolites, dark rocks ---------------

gneiss weathering Gneissic rocks --------------

Widened joints Dark rocks (general) ------------

Alveolar weathering Dark rocks (general) ------------

Angular rock fragments Quartzites (mountain areas) ----------------

Spheroidal weathering Basic dykes --------------

Granular disintegration

shallow General ------------------

deep Basic dykes (general) -------------------

There is generally no measurable material loss connected with the colour changes of the rock. The phenomenon has been observed at almost all of the investigated sites. Usually the difference in colour between fresh rock and weathered parts is fairly slight. At some places the colorations are, however, more prominent. At the location Vårfrukyrka 192 (site 10) there are, for example, intense rusty colours within the rock carving consisting of cup marks. At some other places trickle paths with a distinct surface coloration lies within the investigated areas. This is, for example, the case at Tanum 12 (Aspeberget, site 16) and at Östra Eneby 1 (Himmelstalund, site 23).

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6.1.2. Mineral weathering and pitting

With mineral weathering is meant the selective weathering and disappearance of certain minerals. In the case of, for example, granite it is often the micas at the surface that are gone. Often their disappearance is due to recent chemical attack and chloritization is seen in thin sections (Swantessson, 1992b). In porphyries the phenocrysts at the surface are often gone. The reason can be that there are a large number of micro-cracks around the phenocrysts or that they have a much denser crack pattern than the bulk of the rock. The mineral weathering is associated with material losses, but they are usually very limited since it is an initial stage of deterioration. The phenomenon is, however, easily detected by analysing the roughness data received from the laser scans. Already a minor mineral weathering will increase the calculated roughness indexes compared to a fresh and unaffected rock surface. None of the investigated sites are completely without signs of mineral weathering, except maybe at the rock carving of a horse at Tanum 26 (Aspeberget, site k). ‘Original’ surfaces with still preserved micro glacial striations do, however, occur at several of the studied places but they usually only occupies small parts of the laser scanned areas and are confined to certain minerals that are less susceptible to weathering.

Pitting is rounded holes with the size of about a fingertip and a depth of approximately 1 cm. They have no obvious relation to any particular mineral but are often initiated by the dissolution of opaque minerals. This means that the form is most common in basic rocks (table 7). In connection with the micro mapping of the Bronze Age rock carvings phenomena resembling pitting have only been observed at two sites. These are Östra Eneby 1 (Himmelstalund, site 23) where the bedrock is mica schist and Tisselskog 15 (Högsbyn, Ronarudden, site 19) where the rock is composed of clay slate.

6.1.3. Flaking

Flaking or exfoliation is sheets of a fairly uniform thickness at the surface of the rock that loose contact with the main rock body (figure 34). The phenomenon is reported from all areas of the world and there are several reasons why it occurs. Also at the investigated rock carving sites the active weathering processes creating flaking might differ from place to place. One plausible explanation is chemical alterations near the surface of the rock that cause a slight volume increase and arching-up of the sheets (Swantesson, 1992b). Varying processes at different environments will then be responsible for the ultimate loosening of the sheets and the production of grus. It seems that flaking is most common in fairly massive rocks where the number of joints is limited.

At the investigated sites two distinctly different types of exfoliation have been observed. They are both destructive and seriously threaten the rock carvings. One type is a kind of micro exfoliation of about mm-thick sheets with an area extension of a few square cm. This kind of weathering is, for example, extensive at Tanum 12 and Tanum 18 (Aspeberget, site 16 & j) and at Skee 619 (Jörlov, site 15), where the micro mapped ship figure hardly is visible any more.

The other type involves sheets that are about cm-thick. Scars produced by this type of flaking are commonly seen in nature. At Gamleby 54 (site 2) and at Litslena 194 (Ullstämma, site 9) the extension of such scars has been clearly detected by the repeated

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laser measurements. Also at Tanum 417 (Kalleby, site m) scars caused by flaking are seen. At Boglösa 138 (Rickeby, site 8) failure of the exfoliation sheet had not yet occurred during the last investigation at the place. Here flaking has caused a part of the area that was laser scanned to arch up and to form a hollow space between it and the rest of the rock that easily could be revealed by simple knocking.

Figure 34. Example of flaking, at a location without rock carvings, in gneiss of sedimentary origin at

Enesidan in the south of the county of Stockholm. The outcrop faces E and the sheets can often easily

be detached by hand. Beneath the rock wall grus derived from the decomposition of the loosened

exfoliation sheets is found.

As already mentioned in chapter 5, ‘Site descriptions’, it can in many cases be difficult to distinguish the natural process flaking from damage caused by fire. The degradation of the rock carvings at, for example, Nicolai Församling 340 (Släbro, site 7) and at Skee 619 (Massleberg, site g) is most likely to have been originated by anthropogenic fire. In contrast to the sites where scars caused by exfoliation were extending no significant changes between the consecutive laser scans could be detected at the edges of the damaged area at site 7 (Släbro).

6.1.4. Gneiss weathering

Gneiss weathering is a type of differential weathering that occurs because of the difference in composition, and hence weathering behaviour, between the sheets comprising

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the rock. There are also distinct zones of weakness between the sheets where cracks that can cause failure are more common than elsewhere. The scale of the phenomenon is larger than the mineral weathering and it has a typical depth of a few mm up to a few cm. The only investigated site where gneiss weathering seems to have a major effect on the breakdown of the rock carving panel is at Torhamn 11 (Hästhällen, Möckleryd, site 1), where the schistosity is pronounced. Other types of differential weathering, such as protruding acid veins and minor basic dykes, breaking down faster than the rest of the rock, does not seem to have any significant effect on the present state of the studied places. Neither seems rough surfaces to be clearly associated with any of the investigated objects.

6.1.5. Widened joints

Joints and fissures occur in almost all rock types but the density of them varies. In some fairly soft rocks, such as, for example norite and charnockite it is easily seen that the borders of the joints have been rounded by weathering (figure 35). Also in other rock types breakdown at the edges of joints is more prominent than elsewhere. This is probably aided by a denser crack pattern here, which increases the surface of attack for weathering processes. At most sites with rock carvings, areas with many joints have been avoided by the ancient artists.

Fissures do, however, cross the laser-scanned areas at several of the investigated places. Although it is difficult to assess the exact amount of material losses at their edges with the method used (see chapter 3), it can be said that a continuos breakdown and thereby widening of the joints ultimately severely can destroy the rock carvings. The joint pattern in the quartzite at Järrestad 13 (Dansarenhällen, site 5) and at Simrishamn 23 (site a) is fairly dense. Even if the rock itself is durable this is a factor that can influence the lifetime of the rock art. Other investigated places where widening of joints can be expected to take place are, for example, Lofta 353 (Vittinge, site 3), Boglösa 138 (Rickeby, site 8) and Östra Eneby 23 (Ekenberg, site q).

6.1.6. Angular rock fragments

Alveolar weathering has not been seen in connection with any of the rock carving sites, which can be attributed to the fact that it usually takes place in soft rocks with a dense crack pattern. If rock carvings had been made in such a rock type they would surely already have been disappeared. In table 7 the production of angular rock fragments is restricted to quartzite, mainly in mountain areas. This kind of weathering is, however, common also in other rock types. At, for example, Hovs Hallar at the coast of the Kattegat, about 100 km N of Malmö, decay of the rock in the form of angular fragments is very prominent in orthogneiss (Swantesson et al., 2006b). Here the reason is a dense and irregular joint pattern. At or near the investigated rock carvings the phenomenon has been observed in clay slate at Tisselskog 11 & 15 (Högsbyn, sites 18 & 19), and also, although less obvious, in metasediments at Lofta 353 (Vittinge, site 3) and at the sites at Östra Eneby 1 (Himmelstalund).

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Figure 35. Joints widened by weathering in charnockite at an area without rock carvings on Getterön,

near the town Varberg in the county of Halland.

6.1.7. Granular disintegration

Neither spheroidal weathering nor deep granular disintegration are of obvious reasons connected with any of the investigated sites. They both imply a far-reaching destruction of the rock, meaning that minor anthropogenic forms such as rock carvings not can survive if they ever were made on rocks suffering these types of weathering. In Scandinavia deep weathering can, at certain sheltered places, be remnants of old rock breakdown that have resisted erosion by the land ice. It can also develop in rocks having extremely poor physical and chemical properties where the deterioration process can go very fast.

A shallow granular disintegration is, however, commonly observed at the places that were laser scanned. It is easily detected since grus often lies beneath the slope of the outcrop. Granular disintegration can be defined as processes where sand-sized or finer material is produced. The breakdown can follow the grain boundaries of the rock, but often it follows other crack systems and polymineral grains as well as grus consisting of only parts of the original mineral grains of the rock is common. Other types of weathering often precede the granular disintegration. For example, when a rock has suffered mineral weathering, harder minerals than those already weathered away will loose their support and can thus easily be detached. After a period also sheets produced by flaking will usually fall apart by granular weathering, producing grus.

At some places with granite only a restricted number of mineral grains are lost from the rock carving sites. The sites are in a fairly good state and downwearing rates are reasonably

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low but a limited granular disintegration can be evidenced. Examples of such sites are Gryt 1 (Frännarp, site 4), Brastad 141 (man with big hand, site 11) and Tanum 255 (Fossum, site 17). At some other places the shallow granular disintegration proceeds faster and is a threat to the rock carvings. This is, for example, the case at Vårfrukyrka 192 (cup marks, site 10) and at Foss 6 (Lökeberg, site 13). Also the breakdown in the sandstone at Husaby 70 (Flyhov, site 14) can be considered as a type of granular disintegration. Here the matrix between the sand grains decomposes and the grains loose thereby contact with each other.

6.1.8. Karren forms

Karren forms are minor forms caused by chemical solution of the rock. Such features are not listed in table 7 since these types of forms generally are absent in crystalline rocks. Karren is most common in carbonate rock. The only investigated place with this type of rock is the marble at Ösmo 622 (site 6). There are some indications of karren in the form of minor runnels in the vicinity of the laser scan area here, meaning that solution might be important in the deterioration.

6.2. Reasons for breakdown at the investigated sites It is except in a few particular cases not possible to connect minor deterioration features

with any specific process. Different processes can create similar forms, and chemical weathering usually acts together with physical breakdown. Downwearing by biological activity must as well not be forgotten. Of these reasons just a brief summary, of some aspects that should be born in mind when interpreting the weathering at rock carving sites, follows. The reader is also referred to chapter 5, where main reasons for the breakdown in the particular environment are explained in connection with the description of each site.

Frost action of different kinds can be of importance for the rock breakdown, especially where there are joints. It is also of importance where the surface of the rock already has been attacked by other weathering agencies and has lost its strength and a large number of cracks have been formed. In such cases a temporary cover, during the winter, preventing water from freezing on the rock can be of importance. This measure will, most probably, increase the lifetime of the rock carving panels.

Salts in connection with wetting and drying conditions are capable of intense rock breakdown. The effect is most pronounced near the sea where sea salt spray is blown onto the coast during windy weather. Locations near roads that are salted during winter conditions might be even more susceptible for salt weathering, due to the spreading by passing cars. The only investigated location where this type of downwearing process probably plays the most important role is at Borg 51 (Herrebro, site 20).

Deterioration by man induced ‘acid rain’ is probably not as severe as is often heard in the debate, except maybe at certain very exposed places near the pollution sources. Highly acidic rain water falling on the rock carvings has only existed for a few tenths of years. This means that the sites only have suffered this type of pollution during a fairly short time compared to their total age of about 3000 years. The problems that ‘acid rain’ and other

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kinds of contamination can generate must, however, never be neglected. It might be, for example, that leaves and needles falling on the rock have an effect on weathering rates. When they are wet organic acids are produced and these acids can increase the chemical component of the downwearing processes. Also water trickling over the rock carvings can be acid if it has percolated soil or if it is derived from mire areas. The environment near heritage places must thus be carefully controlled in order to make future deterioration of the rock as limited as possible.

Lichen growth is extensive on many of the studied sites. It also seems that the growth occurs very fast and abundant new lichens have often been formed at the laser scan areas between the consecutive measurements. Whatever the reason for the intense development is, the lichens are increasing weathering rates. Their hyphae can penetrate cracks, where acids are produced at their tips. The hyphae can also detach small rock fragments when the lichens are swelling or shrinking during varying moisture conditions. Bjelland (2002) gives a detailed account on how lichens communities influence rock weathering in Scandinavia.

Anthropogenic influences have in some cases been disastrous. For example, at Västra Tollstad 21 (Hästholmen, site 22) a post for a fence was once placed in the middle of a rock carving. Caustic soda (NaOH) has occasionally been used to remove unwanted vegetation from rock carvings. It is not known exactly where this has been done, but the effects on future weathering can be expected to have been severe. Walking and trampling with shoes on rock carvings can cause an increased downwearing, especially on sites where other types of weathering already are visible and the rock has lost some of its strength. On places with many visitors the public ought to be led to walk next to the carvings instead of across them. Man made fire has also, as mentioned earlier, caused severe damage at some of the investigated sites. Also natural fires can of course be devastating by the detachment of discus-formed fragments and by ‘softening’ the rock so that it easier can be further decomposed by other types of weathering.

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Chapter 7. Status of the investigated rock carving sites In this chapter an attempt to classify the present deterioration status of the investigated

rock carving sites is made. The ranking is made on a scale from 1 to 6, where 1 means a perfectly preserved site without any signs of weathering and 6 that the rock carving is almost destroyed. An explanation of what the ranking numbers means is found in table 8, while the judged status is presented in table 9. Unfortunately it is impossible to avoid a certain degree of subjectivity when presenting a ranking list. Other skilled persons would, however, most probably not have come to radically different opinions. It must also be remembered that the indicated status only refers to the laser-scanned squares and perhaps a few m2 around them. Entire rock carving panels have not been considered. There are often large differences in the intensity of weathering processes and how far they have reached within very short distances.

Table 8. Explanation of the status classification of the investigated rock carving sites. How the

classification was made is described in the main text. The classification itself is found in table 9.

Status Explanation

1 Absolutely perfect fresh state without any dangers for even limited deterioration in the near

future. The conditions for this can only be achieved in controlled indoor conditions and are

never met at exposed sites in nature. Hence, none of the investigated sites have been

assessed status 1.

2 Excellent status without or with only very limited signs of visible deterioration. There will

inevitable be downwearing in the future since the sites are exposed to weathering. The

present status is, however, stable and the rock carvings will survive for prolonged periods

unless environmental factor are changed in a negative direction.

3 The site is in a fairly good state but slight visible deterioration can be detected. There is no

immediate threat of the survival of the rock carvings but of safety reason they ought to be

kept under regular inspections.

4 Sites subjected to present weathering with material losses detected by the repeated laser

scans. The downwearing is, however, fairly limited and the deterioration does yet not

obscure the outlines of the rock carving figures. It might be needed to take measures to

protect these sites in order to limit the future breakdown.

5 Sites seriously threatened by weathering. Figures are still visible but material losses are

fairly large and deterioration, even in the near future, can destroy the rock carvings

completely. Protection measures are urgent.

6 Already destroyed sites. Figures have disappeared completely or there are very large

damaged areas with only limited parts of the original rock carvings left.

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Table 9. Classification of the status of the investigated rock carving objects. The classification is made

on a scale from 1 to 6, where 1 is the best state and 6 the worst (for explanations see table 8). The

major factor for the judgement of the status is mentioned in the column Remarks. For a more complete

description of the deterioration status and possible future developments at the sites the reader is

referred to chapter 5. Repeated laser scans have been made at the sites indicated with a number and

their co-ordinates are found in table 1. Their locations are also seen on the map in figure 5. Only one

measurement has been made at the sites indicated with a letter. Their co-ordinates are listed in table 2 .

Number & site Status Remarks

1. Torhamn 11 (Hästhällen, Möckleryd) 4 Removal of fragments along schistosity

2. Gamleby 54 (in built up area) 4 Extending exfoliation

3. Lofta 353 (Vittinge) 3 Joint across laser scan area

4. Gryt 1 (Frännarp) 4 Some granular disintegration

5. Järrestad 13 (Dansarenhällen) 3 Durable rock, but joints

a. Simrishamn 23 3 Durable rock, but joints

6. Ösmo 622 (Nynäshamn municipality) 5 Weathering due to solution

b. Turinge 441 3 No major visible downwearing signs

7, c. Nicolai 340 (Släbro, Nyköping) 3 Good state, exept parts damaged by fire

8. Bogösa 138 (Rickeby) 5 Exfoliation

d. Boglösa 138 (Rickeby, mantle) 3 Deeply carved figure

e. Boglösa 141 4 Abrasion by vehicles

9. Litslena 194 (Ullstämma) 6 Central parts of figure destroyed by flaking

10. Vårfrukyrka 192 (cup marks) 5 Rusty colours and granular disintegration

11. Brastad 141 (man with hand) 4 Some granular disintegration

12. Brastad 18 (deer figure) 3 No major visible downwearing signs

13. Foss 6 (Lökeberg) 5 Significant material losses

14. Husaby 70 (Flyhov) 5 Significant material losses

f. Husaby 70 (Flyhov, circle-cross) 3 Excellent state but susceptible rock

g. Skee 614 (Massleberg) 2 Excellent state despite some fire damage

15. Skee 619 (Jörlov) 6 Micro-exfoliation, carving almost disappeared

16, h. Tanum 12 (Aspeberget) 5 Micro-exfoliation

i. Tanum 12 (Aspeberget, circle-cross) 4 Clearly visible mineral weathering

j. Tanum 18 (Aspeberget, ship) 5 Micro-exfoliation

k. Tanum 26 (Aspeberget, horse) 2 Excellent state, insignificant weathering signs

l. Tanum 72 (Tegneby, Mellangården) 3 No major visible downwearing signs

17. Tanum 255 (Fossum) 4 Some granular disintegration

m. Tanum 417 (Kalleby) 5 Several different deterioration features

18. Tisselskog 11 (Högsbyn, the meadow) 4 Good state but susceptible rock

n. Tisselskog 12 (Högsbyn, footsole) 3 Excellent state but susceptible rock

19. Tisselskog 15 (Högsbyn, Ronarudden) 4 Good state but susceptible rock

20. Borg 51 (Herrebro) 5 Threatened by salt spray from motorway

21. St Johannes 14 (Egna hem) 4 Limited changes but some damaged parts

22. Västra Tollstad 21 (Hästholmen) 5 Figure damaged by post for fence

23, o. Östra Eneby 1 (Himmelstalund) 3 Weathering signs are relatively few

24, p. Östra Eneby 8 (Fiskeby) 2 Excellent state, insignificant weathering signs

q. Östra Eneby 23 (Ekenberg) 3 Joint across laser scanned area

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Except the calculated material losses several other factors have been considered when judging the status and the possible future development of the investigated sites. Among those are rock types and their properties, aspect, slope, natural environment, human influences and microclimate. This means that, for example, vegetation influences in the neighbourhood and littering from trees have been regarded as well as growth on the rock carvings themselves in the form of algae and especially lichens. Human influences include all man made changes of the natural environment that might alter the progress of weathering at the rock carvings such as nearby roads and buildings. It also includes different kinds of direct actions, of which campfires, excessive walking and trampling, improper management of rock carving sites and also conscious destruction can be mentioned. Some important microclimatic factors are moisture conditions, exposure to the sun and rock surface temperatures. The different factors considered have not been weighed for the judgement of the final status listed in table 9, but the ranking is based on prolonged experience of rock weathering studies.

It can be discussed how representative the choices of the laser-scanned squares are for Swedish Bronze Age rock carvings in general. Although it has been attempted to include various rock types and environments it has not been possible to make a statistically fully correct choice of investigated sites. For this purpose a much larger number of studied places would have been needed which was not conceivable within the limits of the project.

In table 9 it is seen that only few of the studied rock carvings are in an excellent state with no or only very limited signs of deterioration. This can be expected to be the case also in general. It is furthermore believed that the distribution of the other status classes, in table 9, as well roughly corresponds to the conditions at Bronze Age rock carvings in common. At a majority of sites there are minor visible weathering phenomena but the downwearing rates here are not an immediate threat to the figures. Since weathering is a natural continuing process it will with time ultimately obscure the carvings and finally make them disappear at all places.

It is, however, in many cases possible to control and decrease the rates of the deterioration processes by careful management of valuable heritage areas in rock. How this best is done is not yet fully understood. Some rock carvings exhibit extensive weathering damage and are threatened by destruction in the near future. At these places immediate measures are necessary if we want to extend the lifetime. A few of the studied objects are in such disastrous state that they hardly can be considered as heritage objects anymore. It might well be that the number of rock carvings in Sweden once has been much larger than what we know today. If they were carved in soft or already weathered rock or at certain exposed environments with very high downwearing rates, it is likely that they already had disappeared before modern interest in discovering and studying ancient rock carvings started.

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Chapter 8. General discussion and conclusions The results are usually discussed and conclusions are drawn already in connection with

the site description in chapter 5. Chapter 6 and 7 concerning weathering forms and the status of the investigated sites can also be regarded as mainly a discussion about the performed research. Of this reason the discussion and the conclusions in this final chapter is restricted to some general aspects.

8.1. Discussion The research has proved that it is possible to make accurate micro maps of rock surfaces

by laser scanning and also to treat the data statistically in order to compare different sites with each other. This is in itself a great achievement compared to older descriptions of microforms on rock surfaces that has become possible only by the use of modern technique. The only disturbing factor is that the height sometimes not can be detected, or that secondary reflections arise, at abrupt edges when using a triangulation laser. This can, however, fairly easily be overcome by the utilisation of faster scanners. In this case the same area can be measured more than once from slightly different angles, and it is enough if the correct height is found on one of the laser scanned data files.

It has also been possible to calculate average downwearing rates by making repeated measurements at the same site. There have, however, been some difficulties in arriving at those values because of the problems of locating the laser scanner frame on exactly the same spot from one micro mapping to the next. This means that the calculated rates found in chapter 5, ‘Site descriptions’, and in the table in the appendix should be regarded as minimum downwearing values. How the calculations were made and how to interpret the results is described in chapter 4. The main reason for the relocation problem was that no regular studs, of ethical reasons, could be attached to the rock and used within the investigated rock carvings. Minor studs that served as fix points were, however, needed in order to be able to calculate any downwearing rates at all. Their use can be justified since only relatively few sites were micro mapped repeatedly and that it is necessary to find methods by which we will be able to monitor the deterioration of ancient heritage objects in stone.

For future monitoring projects it is inadvisable to use any studs at all. This makes it even more difficult to find reliable relocation methods of a laser scanner or any other type of scientific equipment when making repeated measurements at the same site. The solution probably lies in finding parts of the rock that has not been altered by weathering between micro mapping occasions by sophisticated computer programs. With the help of these unaltered parts it might be possible to make overlays and calculate downwearing rates, perhaps with a better accuracy than what is presented in this research report. It is believed that monitoring of downwearing rates is an essential part for the planning of the management of valuable rock carvings. This is also true for other heritage objects in stone, such as runic inscriptions and buildings. Such research will, however, be of limited value until the relocation problem of measurement devices is fully solved. Careful experimental studies are thus needed.

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Future long time monitoring studies must be accurately planned and the choice of objects for the measurements must be statistically relevant according to rock types and all kinds of environmental factors. Probably up to 100 sites are needed to achieve this. With the use of faster measurement devices it is possible to perform such monitoring of this number of sites on an annual to biannual basis. The geometry of images made with faster laser scanners of the triangulation type is slightly different from the strictly orthogonal projection achieved with the equipment used for the research reported in this publication. Since the laser beam is directed with the aid of a rotating mirror a central projection will instead result, and the distance between recorded height values is somewhat denser near the centre of resulting images than at the periphery. This can cause some problems and, for example, for the calculation of roughness indexes a re-gridding of the data has to be made in order to get a fully regular grid. As mentioned earlier such recalculations unfortunately always lead to some loss of accuracy compared to the original data.

Although some of the localities accounted for in this research report display severe recent decay, average downwearing rates are not alarming. The mean calculated minimum rate for all investigated rock carving sites in Precambrian crystalline rocks is 1.10 mm in 1000 years (Swantesson, 2005). This figure is practically the same as estimates based on measurements of the heights of quartz veins and nodules (Dahl, 1967, Rudberg, 1970 & André, 1996). When another 16 sites, from three coastal locations in Sweden without rock carvings, are added in the calculation we arrive at the somewhat higher downwearing rate of 2.64 mm in 1000 years (Swantesson, 2005 & Swantesson et al., 2006a). The reason might be that breakdown in a coastal environment is faster than inland. The rock here experiences, for example, marine abrasion, intense salt weathering caused by seawater spray and biological weathering where not only lichens are dominating. Gastropod species can in the coastal zone be of great importance for rock decay (Gómez-Pujol et al., 2006 & Swantesson et al., 2006b). Another interpretation of the different downwearing rates is that the rocks where we today find Bronze Age rock carvings usually are fairly resistant to weathering. On places with a faster breakdown the ancient figures are maybe already disappeared.

Perhaps more important than making it possible to calculate downwearing rates are the repeated laser scans for the knowledge of how the micro weathering proceeds. From the overlays of consecutive measurements it is clearly seen that losses of material, within a limited time span of maybe a few years, only occur from restricted parts of the laser scanned squares. Other parts remain unaffected. The influenced areas are usually not larger than a few percent of the total scanned area. It seems that the places where material losses first took place temporarily stabilise, and the micro weathering proceeds by attacking those parts that were previously unaffected. The episodic nature of downwearing rates in time is clearly illustrated at several of the investigated sites. It was, for example, in certain cases seen that all calculated material loss took place between the first and second measurement, while no detectable changes were calculated later, or vice versa. There is thus a great variability both spatially and over time in the intensity of micro weathering. It would never have been possible to study the spatial aspects of the deterioration within small areas, with sizes of only a few dm2, with, for example, the micro erosion meter (MEM). Modern computerised technique is necessary for this purpose in order to be able to obtain enough

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data. The finding of the great spatial variability of the downwearing and the that it takes place episodically is important not only to realise how heritage objects in stone deteriorate but also to better understand how micro weathering works in general.

In the research reported in this publication only the micro weathering has been studied. Downwearing also occurs on a meso- and macro scale. The meso scale downwearing can be said to involve losses of rock fragments with sizes from a few cm up to a few dm, while even larger rock pieces are withdrawn on the macro scale. No damage of these scales has been detected at any of the investigated sites, although the phenomenon fairly commonly is observed in nature. It is, however, evident that if larger scale decay happens it can destroy entire rock carvings instantly. The sites at Tisselskog, Högsbyn (Nr 18 & 19) in clay slate can be considered to be threatened by this type of destruction. We can not know exactly to what extent meso- and macro scale decay has taken place in the past since its quantitative importance is difficult to asses. They are even more episodic than the micro weathering. Events on the meso- and macro scale are, however, most probably of less importance for the general surface lowering than actions on the micro scale in most areas of the relatively flat landscape in southern and central Sweden. This can be assumed by a general knowledge of the intensity of recent geomorphologic processes in these environments.

The study of weathering and downwearing processes is a truly multidisciplinary task, especially when heritage objects are investigated. Experts in earth sciences, chemistry, biology, archaeology and other relevant disciplines need to co-operate. The interaction between natural factors and those that have been induced by man need to be carefully examined. Without a better knowledge it is not feasible to plan adequate management programs to preserve, among others, the Bronze Age rock carvings for as long as possible. Wrong or to quickly taken decisions might in worst cases instead lead to a faster downwearing than if no measures at all were taken.

8.2. Main conclusions Modern technique in the form of laser scanning has made it possible to study the course

of micro weathering on heritage objects in stone at a level of detail that was not previously possible. With older mechanical devices only a limited amount of points could be measured, within an area, compared to many tenths of thousands with the computerised laser scanner equipment. Further technical advances will make the scanning faster and larger areas can be measured with the same, or a better, accuracy. Contour maps, with a contour interval down to 0.2 mm, 3-D models and digital shadow images that can be produced from the data collected in the field are excellent for presentation of the micro mapped Bronze Age figures. Compared to photographs they have the great advantage that measurements of, for example, height differences can be made directly in the images. It has also been successful to calculate roughness indexes of the rock surfaces from the measurement data. Such statistics facilitates comparisons between different areas and can also give clues about for how long time a surface has been subjected to weathering.

Repeated laser scans at the same sites have allowed the calculation of recent minimum downwearing rates. There are very large differences in the speed of deterioration between

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the 26 places where repeated measurements were made. At about 1/3 of the sites no significant breakdown at all could be detected during the eight year long monitoring period. At a majority of the micro mapped areas losses of material could clearly be detected. This can in most cases not be considered as serious since the calculated downwearing rates still are less than the estimated average of 1-2 mm in 1000 years for Swedish crystalline rocks in general. At these places there is no immediate danger that the Bronze Age figures should disappear. Since material losses are clearly revealed the sites need, however, to be looked after regularly. At the remaining places recent breakdown is fast and the sites are threatened by destruction. This will maybe not happen during our lifetime but perhaps in less than 100 years time. It is also seen from the repeated measurements that material losses are episodic. In many cases all breakdown took place during one year, while virtually nothing happened during the rest of the monitoring period.

By subtracting an entire height data grid (micro map) from a previous one taken at the same site a detailed image of where material losses have taken place can be obtained. On these images it is clearly revealed that only limited spots are affected at a time within the measured squares sized about 30x30 cm, while most of the areas are left unaffected. The deterioration then usually ceases at these spots and material removal proceeds at other places. It is very seldom that the downwearing takes places at an even rate over the total scanned area. There is thus generally a great spatial variability in the progress of micro weathering within small areas.

The research has lead to a better understanding about weathering and downwearing rates on natural stone surfaces in southern and central Sweden. It has also shown how the deterioration proceeds. This is of great value when interpreting the status of rock carvings and other ancient objects in stone. Together with other types of investigations concerning similar objects it will help in planning and making decisions about control, management and preservation of these valuable parts of our cultural heritage.

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.5 a

rea

, m

m2

rate

Up

psa

la l

än

8.

Bo

glö

sa 1

38

(R

icke

by)

94

-99

22

3-1

11

9-0

.05

0-

-0

.00

94-0

9-1

595-0

8-1

796-0

7-2

495-9

9819

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67

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91

75

405

0.2

2

97-0

6-2

698-0

8-1

799-0

9-2

196-9

9811

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94

-0.0

46

185

756

0.7

1

02

-08

-06

97

-99

81

3-1

2 0

27

-0.1

48

14

86

0.0

5

98-9

9813

-5 6

21

-0.0

69

--

0.0

0(3

) 99

-02

62

7-4

06

8-0

.06

51

16

1 5

21

0.6

4(4

) 99

-02

24

9-4

02

7-0

.16

22

73

67

0.3

8

9.

Lits

len

a 1

94

(U

llstä

mm

a)

95

-02

60

6-6

89

6-0

.11

44

71

2 6

62

1.1

1

95

-08

-16

97

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-27

02

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-07

97

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64

8+

3 5

61

+0

.05

53

22

23

0.1

0

10

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årf

ruky

rka

19

2 (

cup

ma

rks)

94

-96

37

1-9

32

9-0

.25

38

94

2 5

44

12

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94-0

9-1

496-0

7-2

602-0

8-0

7(5

) 96

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71

4+

1 6

59

+0

.02

3

Västr

a G

öta

lan

ds

län

11

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rast

ad

14

1 (

ma

n w

ith h

an

d)

95

-97

66

2-5

78

2-0

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8-

-0

.00

95-0

9-1

497-0

8-1

5(7

) 01

-08-1

3(6

) 95

-02

200

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44

-0.0

75

--

0.0

0

02-0

8-2

0(6

) 97

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200

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71

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59

--

0.0

0

12

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rast

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18

(d

ee

r fig

ure

)9

5-0

18

49

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98

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66

60

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95-0

9-1

297-0

7-0

701-0

8-1

397-0

1881

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63

-0.0

85

37

240

0.1

0

13

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oss

6 (

Lö

keb

erg

)9

6-0

27

81

-19

37

1-0

.24

81

75

31

0 3

42

3.7

3

96-0

8-0

898-0

8-0

702-0

8-1

7(5

) 98

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477

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63

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04

14

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usa

by

70

(F

lyh

ov)

94

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6 6

15

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06

39

68

47

1 8

03

60

.83

94

-09

-29

96

-08

-04

97

-06

-20

96

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77

0-2

1 0

06

-0.2

73

1 2

75

14

31

02

.46

98

-08

-29

03

-04

-26

97

-03

71

0-2

7 7

06

-0.3

90

1 3

17

19

23

53

.17

98

-03

68

0-2

7 8

33

-0.4

09

1 0

28

15

23

53

.23

15

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kee

61

9 (

Jörlo

v)9

5-0

26

61

-11

93

8-0

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09

38

1 9

91

1.9

8

95

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96

-07

-30

97

-08

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96

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76

0-9

48

9-0

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58

07

1 7

21

1.7

9

02

-07

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97

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76

3-1

4 9

96

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76

62

99

82

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- 9

8 -

Co

un

ty, sit

e a

nd

mo

men

ts o

f m

ap

pin

gp

eri

od

ove

rlap

, cm

2cu

t-fi

ll,

mm

3d

en

ud

., m

m>

.5 v

ol.,

mm

3>

.5 a

rea

, m

m2

rate

Västr

a G

öta

lan

ds

län

16

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an

um

12

(A

spe

be

rge

t -

are

a 1

)9

4-0

25

86

-8 1

26

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39

52

11

64

91

.12

94-0

9-2

895-0

9-1

296-0

8-0

695-0

2590

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75

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27

346

585

0.8

4

99

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02

-09

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96

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64

5+

35

< +

0.0

01

63

10

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99

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75

6-6

16

8-0

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25

37

88

0.2

3

16

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an

um

12

(A

spe

be

rge

t –

are

a 2

)9

6-0

27

39

-7 2

57

-0.0

98

12

17

80

.03

96

-08

-07

99

-08

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02

-09

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99

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75

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8-0

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14

< 0

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16

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an

um

12

(A

spe

be

rge

t –

are

a 3

)9

9-0

27

28

-1 1

49

-0.0

16

25

0.0

1

99-0

8-2

202-0

9-1

4

17

.T

an

um

25

5 (

Fo

ssu

m)

94

-03

71

2-5

63

8-0

.07

91

38

60

.02

94

-09

-28

96

-07

-31

98

-08

-08

96

-03

73

4+

2 8

85

+0

.03

91

31

74

0.0

3

03

-04

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98

-03

73

1+

9 2

40

+0

.12

62

24

0.0

1

18

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isse

lsko

g 1

1 (

Hö

gsb

yn,

the

me

ad

ow

)9

5-9

76

97

-2 7

80

-0.0

40

19

21

00

.13

95-0

9-1

997-0

8-0

8(8

) 99

-09-0

5(1

) 99

-02

82

6+

1 0

01

+0

.01

23

68

56

71

.56

(8) 0

2-0

7-1

1

19

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isse

lsko

g 1

5 (

Hö

gsb

yn,

Ro

na

rud

de

n)

95

-02

47

1-7

57

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18

13

0<

0.0

1

95-0

9-1

897-0

8-1

602-0

7-0

997-0

2499

-441

-0.0

10

65

720

0.3

0

Ös

terg

ötl

an

ds

lä

n2

0.

Bo

rg 5

1 (

He

rre

bro

)9

4-0

9-2

09

4-9

66

88

-9 0

05

-0.1

31

11

81

03

20

.93

94-0

9-2

096-0

7-2

002-0

8-1

3(9

) 94

-02

68

8+

6 0

79

+0

.10

1-

-0

.00

(9) 9

6-0

27

20

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4 4

64

+0

.23

23

53

0.0

1

21

.S

t. J

oh

an

ne

s 1

4 (

Eg

na

he

m)

94

-02

91

4-1

0 8

11

-0.1

18

17

81

54

90

.25

94

-09

-21

96

-07

-21

02

-08

-11

96

-02

93

5-1

0 4

82

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15

12

11

19

10

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22

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äst

ra T

olls

tad

21

(H

äst

ho

lme

n)

95

-02

64

6-6

99

4-0

.10

83

02

89

0.0

7

95-0

8-1

597-0

9-1

802-0

6-2

697-0

2669

-56

-0.0

01

--

0.0

0

- 9

9 -

Co

un

ty, sit

e a

nd

mo

men

ts o

f m

ap

pin

gp

eri

od

ove

rlap

, cm

2cu

t-fi

ll,

mm

3d

en

ud

., m

m>

.5 v

ol.,

mm

3>

.5 a

rea

, m

m2

rate

Ös

terg

ötl

an

ds

lä

n2

3.

Öst

ra E

ne

by

1 (

Him

me

lsta

lun

d)

94

-02

77

0-9

20

8-0

.12

05

66

08

0.0

9

94-0

9-2

196-0

7-1

9

98-0

7-2

696-0

2790

-11 3

95

-0.1

44

101

888

0.2

1

00-0

7-2

802-0

7-0

298-0

2794

-10 0

18

-0.1

26

53

384

0.1

7

00

-02

80

0-1

1 6

47

-0.1

46

91

48

0.0

6

24

.Ö

stra

En

eb

y 8

(F

iske

by)

(2) 9

4-0

2743

94

-09

-22

96

-07

-10

00

-07

-28

96

-02

63

0+

5 6

54

+0

.09

03

25

0.0

1

02-0

8-1

100-0

7-2

8(2

) 00

-02

675

(1)

Du

e t

o r

efle

ctio

ns

of

the

la

ser

be

am

alo

ng

ab

rup

t e

dg

es

of,

fo

r e

xam

ple

, jo

ints

in

corr

ect

he

igh

t va

lue

s h

ave

be

en

re

cord

ed

. T

his

ha

s re

sulte

d i

n

calc

ula

tion

of

inco

ncl

usi

ve d

en

ud

atio

n r

ate

s th

at

are

co

nsi

de

rab

ly h

igh

er

tha

n t

he

re

al d

ow

nw

ea

rin

g.

(2)

A s

atis

fact

ory

ove

rla

p o

f th

e t

wo

me

asu

rem

en

ts c

ou

ld n

ot

be

ach

ieve

d,

ma

inly

sin

ce n

o s

tud

s w

ere

use

d a

t th

is s

ite.

(3)

Th

e c

alc

ula

tion

s re

pre

sen

t th

e lo

we

r p

art

of

the

me

asu

rem

en

t q

ua

dra

ng

le f

or

the

ind

ica

ted

pe

rio

d a

t th

is s

ite.

(4)

Th

e c

alc

ula

tion

s re

pre

sen

t th

e u

pp

er

pa

rt o

f th

e m

ea

sure

me

nt

qu

ad

ran

gle

fo

r th

e in

dic

ate

d p

eri

od

at

this

site

.

(5)

Du

e t

o b

ad

ove

rla

p o

f th

e t

wo

mic

ro m

ap

s it

wa

s n

ot

po

ssib

le t

o c

alc

ula

te t

he

do

wn

we

ari

ng

to

de

pth

s o

f m

ore

th

an

0.5

mm

at

this

site

fo

r th

is

pe

rio

d.

(6)

Un

inte

ntio

na

l mo

vem

en

ts o

f th

e s

can

ne

r d

evi

ce d

uri

ng

me

asu

rem

en

t 2

00

2 c

au

sed

th

at

on

ly 2

00

cm

2 c

ou

ld b

e o

verl

ap

pe

d w

ith o

lde

r m

icro

ma

ps.

(7)

Th

e m

ea

sure

me

nt

fro

m 2

00

1 c

ou

ld n

ot

be

sa

tisfa

cto

ry o

verl

ap

pe

d w

ith a

ny

of

the

oth

er

me

asu

rem

en

t d

ue

to

te

mp

ora

l p

rob

lem

s w

ith t

he

co

ntr

ol

ele

ctro

nic

s.

(8)

A s

atis

fact

ory

ove

rla

p c

ou

ld n

ot

be

ach

ieve

d b

etw

ee

n t

he

me

asu

rem

en

ts f

rom

19

99

an

d 2

00

2 w

ith t

he

tw

o o

lde

r o

ne

s. T

he

re

aso

n is

cau

sed

by

a

reco

nst

ruct

ion

of

the

fra

me

an

d b

y th

e t

op

og

rap

hy

at

this

site

, w

hic

h m

ad

e a

go

od

re

po

sitio

nin

g o

f th

e la

ser

de

vice

imp

oss

ible

.

(9)

Sin

ce it

wa

s im

po

ssib

le t

o r

em

ove

lic

he

ns

com

ple

tely

th

e c

ut-

fill

calc

ula

tion

s h

ave

re

sulte

d i

n h

igh

po

sitiv

e v

alu

es.

Th

e l

ich

en

s a

lso

pro

ba

bly

hid

e

are

as

wh

ere

do

wn

we

ari

ng

ha

s o

ccu

rre

d.