"PIX' ILES 90" NC>l..unéa - Tah:l..t:l... 19 - 24 r1C>'V. 1990

N13

LANDFORM MAPPING OF FORESTED VOLCANIC TERRAIN FROM SPOT XSDATA

CARTOGRAPHIE DE LA MORPHOLOGIE DES SOLS VOLCANIQUES FORESTIERSAPARTIR DES DONNEES SPOT XS

G. R. COCHRANE (1), M. EDWARDS (1), A. PATERA (2)

(1) Geography Department, University of Auckland, NEW ­ZEALAND(2) Italian National Research Council, Italy

ABSTRACT

Parts of many Pacifie islands are characterised bymountainous forested landforms. Rugged terrain, steep slopesand dense vegetation militate against easy access andconventional survey methods using aerial photography andground surveying for mapping purposes. SPOT mul tiband (XS)resolution of 20 metres plus synoptic view of a contiguousarea of 3,600km2 per scene provides an economic, simplealternative for mapping such areas.

New Zealand is an insular Pacifie country but i t is nottropical. Never-the-less it shares in common with tropicalPacifie islands areas of mountainous terrain, covered by densestratified forests with steep slopes and difficult access.High effective precipitation often results in deep gorges andin fine textured dissection especially of softer volcanicrocks.

Examples are given of mapping using New Zealand SPOT datawhere the methods have direct application to tropicalenvironment s .

149, 9 fE~. i996IIMïfïilfül1010003856

using visual analysis techniques SPOT photographie dataprovide excellent first approximation of landforms andgeologic units in areas of difficult terrain such as tropical,

D.R.S. T. O. M. Fends Documentaire

mountainous, oftenvolcanic islands.

heavily forested, deeply dissected,

RESUME

Une partie des nombreuses îles du Pacifique estcaractérisée par des sols montagneux couverts de forêts. Unterrain accidenté, des pentes raides et une végétation denserendent l'accès difficile et inadapté les méthodesconventionnelles d'étude pour les besoins de cartographie. Larésolution de 20 mètres en plus de la vue synoptique d'unezone contigüe de 3 600km2 par prise de vue du SPOT XSapportent une alternative économique et simple à lacartographie de telles régions.

La Nouvelle-Zélande est un pays insulaire du Pacifiquemais elle n'est pas tropicale. Néanmoins, elle partage encommun avec les îles tropicales du Pacifique des zones de solsmontagneux couverts de forêts denses et stratifiées etcomportant des pentes abruptes, le tout étant difficiled'accès. De fortes précipitations entraînent souvent uneérosion à texture fine, surtout des roches volcaniques lesplus tendres.

Des exemples sont donnés sur la cartographie utilisant lesdonnées de SPOT en Nouvelle-Zélande dont les méthodes peuvents'appliquer directement aux environnements tropicaux.

INTRODUCTION

This paper is part of athe geology and geomorphologyfrom SPOT satellite datalandforms by visual analysisaddressed in this paper.

broader research project mappingof the Taupo Volcanic Zone (TVZ)(Cochrane, 1989). Mapping of

of SPOT photographie products is

The TVZ is a complex structural graben of Tertiary andQuaternary volcanics in central North Island New Zealand. Itextends sorne 270km from north to south and varies from 40­120km in west/east width. Broadly known as the CentralVolcanic Plateau this area between Tauranga and Lake Taupo isformed essentially of Pliocene rhyoli tic rocks wi th abundantcineri te and pyroclastic deposi ts from Pleistocene to Recentage.

The New Zealand Geological Survey maps 1:250,000, fig. l ,Rotorua and Taupo, show the area. Plateaux of ignimbrite oftenveneered with pyroclastic pumice or tuff, individual rhyolitedomes, calderas, volcanic centres, lakes in former volcaniccraters, dormant and active composite volcanoes, flankingandesitic mountain ranges, and active geothermal areas aIl

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contribute to the complex patterns present. Active geothermalareas of fumaroles, solfataras, geysers and steam ventsalthough concentrated in the Rotorua Lakes area and theWairakei area near Lake Taupo are spread throughout thecentral plateau (Cochrane and Wan, 1983 ; Mongillo, 1989).

Fig. l shows a generalised map of the northern third ofthe TVZ. The eastern margin of the TVZ is flanked by oldbasement rocks of Mesozoic indurated sandstones (greywackes).These form the uplifted block-faulted highlands of the easternIkawhenua and Raungaere Ranges.

The northwestern boundary is also clearly defined. In thisarea the structural graben of the very f La t Hauraki Plainslowland, formed of late Pleistocene fluviatile current beddedgravels and sands, terminates abruptly on i ts eastern edgeagainst the uplifted western margin of the volcanic KaimaiRange and Mt. Te Aroha volcanic complex. These ranges ofMiocene andesites rise in a dramatic fault line (colour figs.N13G, N13H, N13J and N13K).

Small sedimentary basins occur to the east and north ofthe volcanics (fig. 1, colour figs. N13B, N13D and N13F).

The Tauranga, Maketu and Opotiki sedimentary basins occurto the north between the volcanics and the ocean (f ig . 1, 2and colour figs. N13G.

METHons

SPOT XS scenes (443/426, 444/426 and 444/427) of thenorthern part of the TVZ of North Island, New Zealand recordedon 5 August 1986 were selected for evaluation of the SPOT datafor landform mapping. The data were contrast enhanced andcolour combined (XS 123 : B.G.R.) to produce simulated colourinfrared (CIR) photographie images at 1:100,000 scale. Much ofthe area is forest covered. Visual analysis has included thefollowing processes :

(i) mapping linears(ii) mapping dissection textures to produce a) simple

structural units and b) erosional/lithological units orlandform classes.

Landform classes were mapped from the SPOT scenes basedprimarily on dissection texture patterns.

Measurement of relative relief and prevalent slopes weremade from NZMS 260 Series 1:50,000 topographie maps ofrepresentative subscenes wi thin each of the mapped landformclasses.

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Comparisons were made of dissection texture patterns andstream ordering ranking mappable from the SPOT scenes and theNZMS 260 Series topographie maps.

Landform units mapped from the SPOT scenes were comparedwith NZ geological maps at 1:1 million and 1:250,000 scales.Sorne examples demonstrating the useful role of SPOTphotographie images for the mapping of landforms in difficultterrain are given.

RESULTS AND DISCUSSION

The area selected embraces a diverse range of complexterrain. Mountains, plateaux, hills, interior and coastalplains, interior basins, extinct volcanic cones, estuaries,and numerous lakes are all present. Much of i t is forested.Sorne of it is quite mountainous. Elevations range from 0-1111metres above sea level. These rise much higher in the easternranges beyond the area shown. Although there is a wintermaximum of precipitation i t is relatively evenly distributedthroughout the year. It ranges from 2500-2800mm per annum overmuch of the area (N.Z. Met. Service 1981). Totals are higherdue to orographie effects in the mountains above 600melevation.

Because of length limitations in this paper only a fewexamples from a small but representative range of landformclasses selected from dissected mountain ranges, plateaux andvolcanic dome areas are presented. They demonstrate the usefulrole of SPOT photographie data for the mapping of landforms indifficult terrain. Many other examples are present.

Comparison of fig. l, of generalised landform units, withco1our figs. N13A and N13G of two SPOT scenes covering much ofthe area clearly shows that these broad landform uni ts of Fig1 can be readily subdivided using SPOT images. Similarlyadditional details of landforms can be mapped from colour fig.N13F showing part of SPOT scene 444/426.

SPOT image 444/427 (colour fig. N13A) shows sorne of thiscomplex pattern. Detailed enlarged selections of sorne of thesemaj or landform classes analysed on the basis of dissectiontexture and patterns are shown in colour figs N13B, N13C, andN13D. Boundaries and subdivisions of landforms in SPOT image443/426 (colour fig N13G) are shown as a simple generalisedmap in fig. 2. Satellite and ground photos of the Kaimai Rangeare shown in colour figs. N13H, N13J and N13K. An enlargedsubscene of the extremely dissected western Mamaku Plateau isshown as colour fig. N13I. This differs considerably fromother areas of the plateau (fig. 2, Mamuka plateau areas a, band c).

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OKATAINA VOLCANIC CENTRE

The complex Okataina Volcanic Centre (OVC) including theRotorua Lakes area occupies a central location (fig. landcolour fig. NI3A). It is flanked on the west, north and eastby the Mamaku, Kaharoa, and Kaingaroa Plateaux respectively.Abrupt changes in surface erosion and landform patterns occursouth of the lakes. Variations in landforms are present in theKaingaroa Plateau to the east.

In the enlarged subscene (colour fig. N13C) numerousprominent rhyoli tic domes of early mid-Pleistocene age wi thminimal surface dissection can be seen in the northern half ofthis region. In the southwest of colour fig. N13C the 14kmlong dark gash of the Mt Tarawera eruption vent of 1886 at1111m elevation is shown traversing Mt Tarawera rhyoliticdomes. The still bare unvegetated gravel slopes shown as cyantones. See also colour fig. N13E.

In the northeast thepattern of soft pumiceousan area of steep highinterfluves remain.

finely dissected dendritic drainageKaharoa Plateau lithologies portrayshills. No former plateau surface

Snaking between these areas of dissected hills and therelatively uneroded rhyolite domes the smooth texture of theintermontane lowland depicts the fIat Recent alluvial valleysof the Tarawera River and i ts tributaries. See also colourfig. N13B.

Colour fig. N13E shows a ground photo from the Mt Taraweraexplosion vent looking northeastwards over the lower dissectedhills, past the Recent Volcanic cone of Mt Edgecumbe (colourfigs. N13A, N13B and N13F), across the Quaternary sedimentarycoastal Whakatane lowlands to the Bay of Plenty (colour fig.N13F). In the extreme northwestern corner is the active WhiteIsland volcano, a coastal outlier of the TVZ.

This central OVC area is flanked on the east and the westby the structurally simpler Kaingaroa Plateau (colour figsN13A, N13B and N13C) and the Mamaku Plateau (colour figs.N13G, N13J and fig. 2) . These are formed of younger mid­Pleistocene predominantly ignimbrite rocks. The Kaharoaplateau flanking the OVC to the north is formed of stillyounger late mid-Pleistocene poorly compacted pumiceousbreccias. Surface dissection is complexe Much of the area isof an intensively dissected hilly nature rather than a plateausurface (colour fig. N13F).

KAINGAROA PLATEAU

Surface erosional patterns of the Kaingaroa Plateau shownon the SPOT photographic product contrast dramatically between

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the northern (colour fig. N13B), middle (colour fig. N13D),and southern sections (colour fig. N13A).

The northern third of the Kaingaroa Plateau (fig. 1) seenas a SPOT subscene image in colour fig. N13B is characterisedby a high densi ty dendri tic drainage pattern and very finetextured dissection pattern. The surface is one of dissectedlow hills with numerous ridges, shallow valleys and lowrelative relief. No original plateau surfaces exist asinterfluves. Narrow ridge crests prevail. The eastern marginsare flanked by the downfaul ted alluvial Te Mahoe and Waiohaubasins and the upfaul ted western edge of the central axialgreywacke ranges (fig. land colour fig. N13B). The plateau isterminated to the north by the very recent symmetric cone ofMt Edgecumbe and the alluvials of the Whakatane lowland. Tothe west the coarse ranges and the domes of the OkatainaVolcanic Centre together form western boundaries.

The central area of the Kaingaroa Plateau west of thedownfaul ted Galatea Basin ( fig. 1) provides a considerablecontrast (colour fig. N13D) to the northern part (colour fig.N138) . Drainage is strongly oriented as a series of largepar a I Le L widely separated easterly flowing streams in deeplyincised narrow gorges. There is very limited lateral tributarydevelopment.

Thus broad plateau surface interfluves, transversely cutby widely spaced deep narrow paraI leI gorges characterise thesurface (colour fig. NI 3D ). Landform features differ greatlyfrom the area immediately to the north (colour fig. N13B).Similarly this central area with its characteristic assemblageof landform characteristics differs considerably from thesouthern third of the Kaingaroa Plateau. The southern third ischaracteristically a very fIat, wide plateau surface withminimal stream dissection other than at the eastern andwestern fault margins (colour fig. N13A). The SPOT imageclearly facilitates mapping the Kaingaroa Plateau landformuni t (fig. 1) into three distinct and separate uni ts (colourfigs N13A, N13B and N13D).

AXIAL GREYWACKE MOUNTAIN RANGES

The Kaingaroa Plateau is in its turn flanked on the eastby the block- faul ted, fractured and deeply dissected horst ofpart of the North Island' s central axial mountain ranges ofbasement Mesozoic greywackes. Strong evidence of structurallyfault controlled coarse trellised primary drainage patternswith a secondary dendritic pattern (colour fig. N13F) isevident (colour figs. N13A, N13B and N13D). This landform unitis readily recognised also by its coarse textured dissection,strong concordance of summi t levels, a characteristic largerelative relief and the dramatic faulted western edge (colourfigs. N13A, N13B, N13D and N13F).

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MAMAKU PLATEAU

Strong contrasts in landform areas are present in the areacovered by SPOT scene 443/426 (colour fig. NI3G). The MamakuPlateau occupies much of the eastern half of this area (figs.1 and 2). Colour figs. N13G and N13H show that the MamakuPlateau area has a varied range of landforms and is much morecomplex than the simple pattern derived from the NZ GeologicalMap (Healy et al., 1964) as shown in fig. 1. Formed of weaklywelded ignimbrite this plateau dips gently to the north from amaximum elevation of near 600m in the south. In the westerosion is severe from the numerous westward drainingtributaries of the Waihou River. Frequent narrow par a LLe Lvalleys closely dissect the southern part. The valleys riselaterally very steeply to narrow crests and alternating narrowinterfluve areas (colour fig. N13I). An intermediate form withnarrow moderately deep U-shaped gorges with broaderinterfluves characterises the central lower Kaimai (area b infig. 2). One of New Zealand's major kiwifruit orchard areas islocated in the north at Te Puke (c in fig. 2) on gentlysloping broad interfluves. Steep hills in the north withdendri tic drainage, an adj acent qui te mountainous area and alarge domed area (rhyolite) in the south wi th only minimalsurface erosion (colour fig. N13D, N13G and N13I) are clearlydifferent landform units wi thin the broad generalised MamakuPlateau division of fig. 1.

HAURAKI PLAINS AND KAIMAI RANGES

To the west of the Mamaku Plateau, the Hauraki Plainsgraben, and the horst of the western edge of the Kaimai Rangeand Mt Te Aroha mid-Tertiary andesi tic volcanics form sharplandform boundaries. They also add to the complexity anddistinctiveness of the landform units. The Hauraki Plains,formed of very late Pleistocene current bedded sedimentaries,is one of the flattest areas in New Zealand (colour figs.N13G, N13H, and N13K). The coarsely dissected andesitic rocksof the northern half of the Kaimai Ranges rise abruptly asforested mountains to over 1000 metres at Mt Te Aroha (colourfigs. N13G and N13H).

Broad open valleys (colour fig. N13H), few tributaries anda high relative relief characterise the landforms of the mid­Tertiary andesites of the Kaimai and Te Aroha volcanic complexforming the dramatic faul t edge of the northern part of theKaimai Ranges (colour figs. N13G, N13H, N13K, and fig. 2).These differ from the short steep valleys with narrowtransverse profiles of the strongly welded Plioceneignimbri tes forming the eastern flanks and southern edges ofthe Kaimai Ranges (figs. N13J and N13K). Surface dissection ismuch less than on the weakly welded mid-Pleistoceneignimbrites of the Mamaku Plateau immediately to the east.

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CONCLUSION

SPOT XS photographic products at scale of 1:100 000 wereused for landform mapping primarily using dissection textureto map landform classes. Much of the area is mountainous anddensely forested. This analysis demonstrated that thetechnique is practical and economic. It provides a usefulfirst approximation for landform mapping where data may besparse or lacking. It is useful for updating existing maps.It is especially valuable for mapping areas of rugged terrainand difficul t access. SPOT products are superior to LANDSATRBV for landform mapping (Cochrane & Browne, 1981).

The resul ts from this analysis share common problems ofmapping forested volcanics of many Pacific islands. Thetechnique requires minimal equipment and uses conventionalphoto interpretation and photo geological techniques to mapareas of difficult terrain. The spatial resolution of the SPOTXS data plus the synoptic view provides a better tool for anda more rapid method of broad geological mapping of structures,dissection textures and landform classes than does aerialphotography. Preliminary comparison of mapped landforms wi thgeological and topographic maps show good agreement with moredetail usually present on the SPOT photographic products.Further field mapping suggests that updating, improvement, andmodification of sorne existing maps is likely.

The use of SPOT PAN products has not been tested.Potentially such data should provide even better resul ts formapping landforms. Future plans include digital analysismerging SPOT PAN, LANDSAT Ttvl and digital terrain data (DTM)for detailed landform mapping. Al though more rapid and veryacurate and detailed such analyses are dependent upon accessto sophisticated image processing facili ties and interactivesoftware such as "IGIS" (Cochrane, 1989).

ACKNOWLEDGEMENTS

The authors wish to thank Jonette Surridge, University ofAuckland Department of Geography for draughting, and BrianHurst, Department Photographer for photographic assistance.Dr. A. Patera acknowledges financial support from the ItalianNational research Council. The University of Auckland ResearchCommittee provided Professor G. Ross Cochrane wi th researchsupport which is gratefully acknowledged.

REFERENCES

COCHRANE G. Ross, 1989. IGISgeological mapping. Unpublished paperGeography Conference Dunedin.

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Image processingpresented at 15th

forNZ

COCHRANE G. Ross, G.H. BROWN, 1981. Geomorphic mappingfrom LANDSAT III Return Bearn Vidicon (RBV) Imagery.Photogrammetrie Engineering and Remote Sensing 47 : 1205-1213.

COCHRANE G. Ross, T.F. WAN, 1983. Interpretation ofstructural characteristics of the Taupo Volcanic Zone, N. Z.from LANDSAT data. International Journ. of Remote Sensing 4(1)

111-128

HEALY, J., J.C. SCHOFIELD, B.N. THOMPSON, 1964. Sheet 5,Rotorua, Geologica Map of N.Z., 1:250 000, DSIR, WellingtonMongillo M.A. 1989. Video Thermal Infrared Surveys Of NewZea1and Geothermal Areas. Proeeedings 15th NZ GeographyConference: 230-234.

N.Z. MET. SERVICE. 1981. Summaries of ClimatologicalObservations to 1980. NZ Met. Service Miseell pub. 177.

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WESTERN UPLANDS

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Figure 1 Genera1ised landform categories of Central VolcanicZone (CVZ), North Island, N.Z. Geological Survey map (Healy etal., 1964).

c

o Bayai Plenty

MAMAKU PLATEAU

a

10km1

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Figure 2 Genera1ised map of landform units of colour fig.N13G based on analysis of dissection textures.

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~13

N138 : SPOT subscene showing finelydissected but not deeply incisednorthern part of Kaingaroa Plateauflanked by coarse ranges to westalluvial lowlands to north , andbasins and greywacke ranges to theeast.c CNES 86/Dist. SPOT IMAGE

N13A : SPOT XS scene444/427 of part of CVZ.Okataina volcanic moun­tain and Lake complex(west, left ) ; KaingaroaPlateau (centre) andIkawhenua Ranges (easternmargin).c CNES 86/Dist.SPOT IMAGE

N13C : SPOT subscene ofRotorua lakes - rhyolitedome mountain complex.Note the limited erosionon the domes, the baregravel slopes and thelong dark gash of Mt .Tarawera crater in thesouthwest and theTarawera River alluvialvalleys in the northeast.c CNES 86/Dist.SPOT IMAGE

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N13

N13E : Ground view looking north eastalong Mt. Tarawera explosion chasm,across the lower dissected hills tothe volcanic cone of Mt. Edgecumbe.The Whakatane lowlands and Bay ofPlenty lie beyond.

Nl3D : SPOT subscene ofthe central KaingaroaPlateau (western twothirds), Galatea Basinand Ikawhenua Ranges.Note the coarse paraI leIdrainage on the plateau.c CNES 86:Dist.SPOT IMAGE

N13F : SPOT subscene(west-Ieft to east).Finely dissected volcanichills Whakatane Lowlandwith Tarawera, Rangitaikiand Whakatane rivers andfaulted coarsely dis­sected greywacke Raun­gaeke Range.Mt. Edgecumbevolcanic cone is conspi­cuous near the centralsouthern edge.c CNES 86 jDist.SPOT IMAGE

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N13

N13H : Ground view from HaurakiPlains looking east to the coarsebroad valleys of the faulted westernedge of Miocene andesites of thenorthern part of the Kaimai Range.See colour figs. N13G, N13K andfig. 2.

N13G : SPOT scene443/426 of part of CVZ.Compare with fig. 2c CNES 86/Dist.SPOT IMAGE

Nl3I : Westward flowingtributaries of the WaihouRiver have carved deepsteep-sided paraI leI gor­ges into the forest cove­red western par of theKaingaroa Plateau. Thenorthern central area isa forest clad massiverhyotitic dome with veryshallow widely spacedcoarse drainage patterns.Predominantly paraI leIdrainage in deep gorgesreappears ~n .the forestedKaingaroa Plateauignimbrites in the northeast. Pastures (pink.tones) cover the lowlandson the west.c CNES 86/Dist.SPOT IMAGE

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N13

N13J : Faulted western margin offorested southern Kaimai Rangesformed of highly welded Plioceneignibrites. See colour fig. N13K.

N13K :SPOT subscene ofHauraki Plains KaimaiRanges and Tauranga lowlands. Note contrastsbetween northern andsouthern parts of theKaimai Range. Comparewith colour figs. N13Hand N13J.c CNES 86/Dist.SPOT IMAGE

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"PIX'ILE 90"

Journées internationales tenues à Nouméa· Nouvelle-calédonieetà Tahiti· Polynésie Française

19/24 novembre 1990

International workshop held at Noumea • New caledoniaand Tahiti French· Polynesia

November19/241990

ilt:EAfER

© ORSTOM, Nouméa. 1992

Irnprimo par le Centre ORSl DMde Nouméa

Septembre 1992

'"IORSTOU Hou.....~.-:EPROGRAPHIE