Understanding the shallow pathways of the hot spring waters in ...

Understanding the shallow

pathways of the hot spring waters

in Chaiya, Surat Thani

a DAAD RISE-worldwide research internship

August - Oktober 2016

Supervisor: Dr. Helmut Duerrast

Prince of Songkla University, Thailand

Participant: Alicia Rohnacher

Karlsruher Institute for Technology, Germany

Contents

1. Erfahrungsbericht- ein Praktikum in Thailand 4

1.1. Reisevorbereitungen . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.1.1. Visum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.1.2. Gesundheit und Impfungen . . . . . . . . . . . . . . . . . . . 5

1.1.3. Wohnung . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1.1.4. Sprache . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1.2. Leben in Thailand . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

1.2.1. Hat Yai . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

1.2.2. Prince of Songkhla University . . . . . . . . . . . . . . . . . . 6

1.2.3. Essen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2. Abstract 8

3. Literature Review 9

3.1. Physical Background . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

3.2. Geoelectric Measurements . . . . . . . . . . . . . . . . . . . . . . . . 10

3.3. Geothermometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

4. Objective 14

4.1. Geological setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

4.2. Aim of study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

5. Methods 17

5.1. Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

5.2. Geoelectrical fieldwork . . . . . . . . . . . . . . . . . . . . . . . . . . 17

5.2.1. 1-D measurements . . . . . . . . . . . . . . . . . . . . . . . . 18

5.2.2. 2-D measurements . . . . . . . . . . . . . . . . . . . . . . . . 19

6. Results 21

6.1. Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

6.2. Geoelectric surveys . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

6.2.1. 1-D measurements . . . . . . . . . . . . . . . . . . . . . . . . 22

2

6.2.2. 2-D measurements . . . . . . . . . . . . . . . . . . . . . . . . 23

7. Discussion 27

8. Conclusion 30

9. Acknowledgements 31

Appendix i

3

1. Erfahrungsbericht- ein Praktikum

in Thailand

Das RISE-weltweit Stipendium bietet eine großartige Möglichkeit, wissenschaftlichen

Fragestellungen nachzugehen und dabei andere Länder und Kulturen kennenzuler-

nen. Die Arbeit an meinem Projekt mit Planung, Feldmessungen und Auswer-

tung hat mich in meiner Studienwahl bestätigt und mir gezeigt, wie vielfältig geo-

physikalische Untersuchungen sein können. Zusätzlich habe ich ein faszinierendes

Land mit tollen Menschen getroffen mit denen ich hoffentlich auch in Zukunft Kon-

takt haben werde. Zuerst war meine Reise vielleicht ein Sprung ins kalte Wasser,

aber ich habe tolle Erfahrungen hier machen können und diesen ’Sprung’ somit nie

bereut!

1.1. Reisevorbereitungen

1.1.1. Visum

Für ein Praktikum in Thailand bietet sich das ’Non-Immigrant’-Visum mit dem

Zusatz ’ED’ für Education an. Es erlaubt einen 90-tägigen Aufenthalt in Thailand.

Man kann das Visum 1 Jahr, oder 3 Monate vor der Einreise beantragen, wobei die

zweite Möglichkeit günstiger ist. Der Antrag muss persönlich in der Botschaft oder

einem Konsulat gestellt werden. Ein Einladungschreiben von der Universität ist zu

empfehlen, dabei muss mit dem Konsulat eventuell abgeklärt werden, ob auch ein

Dokument in thailändischer Sprache akzeptiert wird.

Weiter Infos sind unter:

http://thaiembassy.de/site/index.php/konsularwesen-visa-beglaubigungen/

wie-man-ein-visum-beantragt

zu finden.

4

http://thaiembassy.de/site/index.php/konsularwesen-visa-beglaubigungen/wie-man-ein-visum-beantragt

http://thaiembassy.de/site/index.php/konsularwesen-visa-beglaubigungen/wie-man-ein-visum-beantragt

1.1.2. Gesundheit und Impfungen

Ob Impfungen notwendig sind, sollte am besten mit dem Hausarzt oder einem

Tropeninstitut o.ä. abgeklärt werden. Es kann sein, dass mehrere aufeinander-

folgende Impfungen gebraucht werden, sodass es sinvoll ist, sich früh genug darum

zu kümmern. Vor Ort selbst sollte man sich ins Bewustsein rufen, dass eine medi-

zinische Versorgung zwar vorhanden ist, jedoch (oft) nicht auf dem Standard, den

wir in Deutschland gewohnt sind.

Es bietet sich auch an, für kleinere Krankheiten selbst eine Reiseapotheke mitzunehmen.

Neben den gewöhnlichen Medikamenten gegen Erkältungen und Ähnlichem sollte

mit dem Arzt abgesprochen werden, ob ein Medikament wie ’Malerone’ zur Prophy-

laxe oder Behandlung von Malaria mitgenommen werden sollte. Auf der Website

des Auswärtigen Amts wird die Provinz Songkhla, in der sich Hat Yai befindet,

ganzjährig als Malariagebiet eingestuft. Auch das Dengue-Fieber kann durch einen

Mückenstich übertragen werden. Deshalb ist es sinnvoll sich gegen Stiche zu schützen;-

mit einem gutem Insektenschutzmittel (hoher DEET-Gehalt) und dem Tragen von

langen Hose/ langärmligen Oberteilen, falls man sich viel im Freien aufhält.

1.1.3. Wohnung

Am einfachsten ist es, wenn man sich bei dem Betreuer vor Ort erkundigt, ob er

einen Vorschlag für ein Zimmer hat. In der Universität gibt es auch Wohnhäuser

für Studenten, jedoch ist er hauptsächlich für Studenten gedacht, die ein ganzes

Semester oder Jahr bleiben. Außerhalb werden viele Appartments oder Zimmer

angeboten. WG’s sind hier eher unbekannt.

Bei den meisten Zimmern, die man mieten kann, ist keine Küche dabei, sodass man

sich mit einem eigenen elektrischen Kochtopf behelfen muss oder sich Essen auf

einem der vielen Märkte oder Essenläden kauft.

1.1.4. Sprache

Der thailändischen Sprache liegt ein anderes Alphabet zugrunde und beim Sprechen

ist wie in vielen asiatischen Ländern die Betonung sehr wichtig. Während meiner

Zeit in Thailand habe ich mir oft gewünscht, vorher einen Sprachkurs besucht zu

haben. Denn die meisten Menschen sprechen kein oder kaum Englisch. Selbst

in der Universität ist es teilweise nicht möglich, sich mit Bachelor-Studenten zu

5

unterhalten. Gerade aber für das Einkaufen auf den Märkten ist es sinnvoll sich ein

paar Vokabeln zurechtzulegen.

1.2. Leben in Thailand

1.2.1. Hat Yai

Hat Yai ist eine der größten Städte im Süden Thailands und befindet sich in der

Proinz Songkhla. Zur Grenze nach Malaysia sind es nur knapp 60km. Das Auswär-

tige Amt warnt jedoch vor den südlicheren Gebieten in Thailand, in denen es schon

öfters zu Anschlägen gekommen ist. Daher sollte man diese Regionen meiden! Mit

dem Auto sind es nur 30 Minuten in die Provinzhauptstadt und ans Meer.

Die einzige Zugverbindung im Süden Thailands führt durch Hat Yai und verbindet

Bangkok mit Städten in Malaysia. Von Hat Yai aus werden sowohl einige nationale

Flughäfen als auch international Flughäfen angeflogen.

Vor Ort kann man sich selbst einen Motorroller oder ein Fahrrad (in der Uni

möglich!) zur Fortbewegung leihen oder auf Taxis, Tuk-Tuks oder Motorrad-Taxis

zurückgreifen.

Die Temperaturen sind im August- Oktober meist zwischen 25°-35°C, erscheinen

aber durch die hohe Luftfeuchtigkeit noch höher. Es ist auch der Beginn der Regen-

zeit, sodass auch mit starken Regenfällen gerechnet werden muss.

Hat Yai ist kein Touristenzentrum, was auf der einen Seite ermöglicht das Land und

die Leute an sich gut kennenzulernen aber auf der anderen Seite bedeutet, dass kaum

Menschen Englisch sprechen und die Fortbewegung innerhalb der Stadt schwieriger

ist.

Ich habe hauptsächlich nur gute Erfahrungen mit den Thailändern hier gemacht,

die meist hilfsbereit und freundlich reagieren. Trotzdem kommt es vor (gerade bei

offiziellen National Parks oder Tempeln), dass man als Ausländer mehr bezahlt, als

ein Thailänder.

1.2.2. Prince of Songkhla University

Die Prince of Songkhla University ist die größte Universität im Süden und besteht

neben dem Hauptcampus in Hat Yai noch aus 4 weiteren Campussen.

Ein Bachelor-Studium dauert normalerweise 4 Jahre und die Studenten tragen Uni-

formen. In meinem Fall musste ich aber keine Uniform tragen, da man durch das

Projekt nicht an der Lehre teilnimmt und bei der Forschung hauptsächlich Kontakt

zu Master- und PHD-Studenten hat.

6

Es gibt eine Gruppe für ausländische Studenten (International Student Association),

die verschiedene Aktivitäten organisiert. Am besten lässt man sich in die Facebook-

Gruppe einladen oder in den E-Mail-Verteiler aufnehmen.

Im Physics Department gibt es einen überdachten Innenhof in dem mehrere kleine

Läden günstige Gerichte für die Mittagspause anbieten. Größere Auswahl an Läden

gibt es in dem ’Food court Rong Chang’, mitten in der Universität.

Es gibt zahlreiche Sportmöglichkeiten, unter anderem mehrere Tennisplätze und ein

großes 50m-Schwimmbecken.

1.2.3. Essen

Der Hauptbestandteil der thailändischen Mahlzeiten ist Reis;- und zwar morgens,

mittags und abends. Dazu gibt es oft Gemüse oder diverses Fleisch. In den Su-

permärkten gibt es aber auch das übliche Toastbrot oder sogar Müsli, wobei das

meist teuer aus Europa importiert wird. Falls man nicht in der Uni isst oder keine

Möglichkeit hat, selbst zu kochen, kann man sich an einem der vielen Straßenstän-

den oder den Restaurant etwas kaufen. In der Supermarkt ’Seven11’ können auch

Mikrowellengerichte aufgewärmt werden.

Im Allgemeinen ist das thailändische Essen sehr gut, jedoch teilweise auch sehr

scharf.

Man muss immer bedenken, dass andere Hygienestandards gelten, als in Deutsch-

land, aber wenn man ein bisschen vorsichtig ist, hat man damit kein Problem.

Wichtig: Anders als in Deutschland kann man Leitungswasser hier nicht trinken!

7

2. Abstract

Geothermal fields as energy resource are an important topic for energy production

in the future. Thus, areas with geothermal activity have to be found and explored.

This study is using geoelectric measurements to describe the hot springs in the

Chaiya region in the province of Surat Thani in Thailand. The shallow subsurface

in the area has a low resistivity and a high water content. Water samples indicate

that they have one common water reservoir in the depth. A minor fault is enabling

the upflow of the water and causes a vertical displacement of the subsurface layer.

At the surface a carbonate crust and carbonate deposit on algae in hot pools can be

found. Furthermore, there are marks that the water is transporting sand up from

the depth.

8

3. Literature Review

With geophysical methods it is possible to gain information about structures in

the subsurface. Geoelectric measurements are an important method, which take

advantage of the resistivity differences of various materials.

3.1. Physical Background

In active geoelectric measurements electric current will be led through the soil and

the potential will be measured. An electric current is nothing else than the movement

of electric charges, - electrons or ions. For movement of electrons (electronic current)

the material must be conductive itself, while ions also move in fluids (electrolytic

current). The second type of current is effected by the porosity and the saturation

of a medium and plays an important role in the environment and especially in soils

with a high fluid content.

With Archies Law the relationship between the resistivity ρ of a porous medium

and its porosity Ψ can be found:

ρ = ρwa

Ψm

F

(3.1)

a and m are empirical parameters.

Generally it can be assumed, that a higher water content in porous material is fol-

lowed by a higher conductivity. (Loke, 2015)

The resistivity is the reciprocal value of the conductance, which describes the ability

of material to conduct electric current. In contrary to the resistivity ρ, the resistance

depends on the geometry of the measurement.

A closer look to the potential field of a current source will explain this statement

(refering to the skript of the University Munich). For a point source in an homoge-

neous half space with currency I, the potential field U can be found:

U(r) =I ρ

2π r(3.2)

9

The difference of the potential of two points r1 and r2 is then given by

U(r1)− U(r2) =I ρ

2π

(

1

r1−

1

r2

)

=I ρ

K(3.3)

K describes the geometry of the configuration and is called ’geometry factor’.

As a result, the resistivity can generally be described with:

ρ =U

IK. (3.4)

3.2. Geoelectric Measurements

In geoelectric field studies normally four electrodes are used. Two (C1 and C2) are

inserting the current into the subsurface and between the other two (P1 and P2) the

potential will be measured. Thus, equation 3.3 develops to:

U(P1)− U(P2) =I ρ

2π

((

1

rC1P1

−1

rC2P1

)

−

(

1

rC1P2

−1

rC2P2

))

(3.5)

= I ρ1

2π

(

1

rC1P1

−1

rC2P1

−1

rC1P2

+1

rC2P2

)

(3.6)

=I ρ

K(3.7)

with K = 2π(

1

rC1P1

−1

rC2P1

−1

rC1P2

+ 1

rC2P2

)

−1

.

Depending on the objective, different array types can be chosen. The most two

common types for a 1-D survey are the Wenner and the Schlumberger array. They

are described in Berckhemer (1990). In both constellations the electrodes form one

straight line. The current electrodes are at the outside, while the potential elec-

trodes are in the middle of the line. For the Schlumberger array the position of the

potential electrodes will be generally constant and the current electrodes increase

their distance logarithmically. The farer the distance between the current electrodes,

the deeper is the current flowing. Thus, the Schlumberger array is normally used

for vertical soundings. As seen in Figure 3.1, the current electrodes were generally

called A and B and the potential electrodes M and N .

In contrast, the distance a between all of the electrodes in the Wenner array is con-

stant (Figure 3.1) and the electrodes were moved together along the survey line. It

is a good choice to record lateral changes.

For a 2-D measurement a Wenner and a Schlumberger array can be combined. But

there are also other arrays, which can be used. There are all shown in Figure 3.2.

10

Figure 3.1.: Schlumberger array on the left and Wenner array on the right. Modifiedafter Lowrie (2006).

Because in this study the dipole-dipole array was used for the 2-D measurements ,

Figure 3.2.: Different arrays used for geoelectrical surveys (Loke, 2015).

further explanations (based on Loke 2015) will only be provided for this array.

Also for the dipole-dipole array the electrodes will normally be put in a straight

line. But in contrary to the Wenner and Schlumberger array, C1 and C2 are next to

each other and P1 and P2 are moving.

A measurement can be divided into several sections. In every section the position

of C1 and C2 is constant and their distance is called ’spacing’ a. At the first mea-

surement all the electrodes have the same distance to each other and with every

measurement the distance between the current and potential electrodes increases

about a. So the distance between C1 and P1 can be described with n · a. Normally

n is a integer value between 1 and 8; for higher n, the signal strength can be too

11

weak for measurements.

The depth of investigation to which the measured data refer, can be calculated by

looking at the sensitivity function of the array. The sensitivity describes the influence

of a change in the resistivity in the soil on the the measured potential. McGillivray

and Oldenburg (1990) described the sensitivity function with the Frechet derivative

for 1-D and 2-D problems. Figure 3.3, provided by Loke (2015), shows the 1-D

sensitivity function of a Wenner array. The median depth of investigation is there

described with the ratio between the depth and the electrode spacing for which the

integral of the function is divided in two areas with equal size. For the dipole-dipole

Figure 3.3.: 1-D sensitivity function (Loke, 2015).

array the depth of investigation for the different n values can be found in Loke

(2015).

3.3. Geothermometer

With the Geothermometer the temperature of a geothermal reservoir can be calcu-

lated by assuming equilibrium conditions between different ingredients of the water.

Fournier (1989) discussed among others the silica geothermometer and the cation

geothermometer. The silica geothermometer is depending on the solubility of silica

solids as quartz in the water. Different empirical equations could be introduced for

12

different geological settings. The two main important for calculating the reservoir

temperature T (in °C) are:

T =1309

5.19− log(S)− 273.15 (3.8)

T =1522

5.75− log(S)− 273.15 (3.9)

S describes the silica content (in mg

kg) in the water sample. Both equations were

found by Fournier (1977) and can be used for reservoir temperatures under 250 °C.

Equation 3.8 is chosen, when there is no steam loss at the spring , which means, the

water is mainly cooling by conducting. Equation 3.9 is used when the water also

cooled adiabatically via boiling.

With the reservoir temperature Tres, the temperature of the soil at the surface Tsur

and the geothermal gradient (dTdz

) the depth z of the reservoir can be calculated:

z =Tres − Tsur

dT

dz

(3.10)

13

4. Objective

4.1. Geological setting

Figure 4.1.: Map of the explored hot springs. Locations show a trendline of thesprings. Map modified after Imagery and Thailand’ (2000)

Hot springs are located in the district Chaiya north of the city Surat Thani (refer

to Figure 4.1). In the study area several hot springs can be found (for the coordinates

refer to the appendix). Some of them are not in their natural shape due to human

influence. It can be recognized, that their positions follow a general trend leading

NW-SE.

In Figure 4.2 it can be seen, that the study area is bounded in the south-west by

a small sandstone mountain, leading in the same direction as the trend line. The

slope of the mountain is at its north-west side very steep.

In view to measurements it has to be considered, that the N-S leading railway is

dividing the study area and has a influence of the feasibility of possible survey lines.

West of the railway trees have been cut in an 450 m long and 60 m wide strip.

During a geological survey additional information could be collected for introducing

a basic subsurface model. Soil sample suggest, that next to the surface clay and

silt layers can be found. The mountain indicates that there is also sandstone in

the subsurface and due to some limestone outcrops in close quarrys and limestone

14

Figure 4.2.: Study area

mountains in the area (Figure 4.1), limestone formations can not be excluded.

The hot springs (D and E), which do not seem to be influenced by humans, have a

terrace structure. The outflow is slightly higher the the surrounding and the water

is flowing on the top of the surface in the closer area of the spring. This structure

seems to develop through sand production of the hot spring. Sand is transported

up with the water and deposits on the surface. Other known phenomena with

material transport in geothermal regions are mud pots and mud volcanoes. Their

characteristics were i.a. discussed by Dimitrov (2002) and their activity is normally

linked with the interaction of gas and water. In the most discussed cases mud, mostly

consisting of clay, is flowing out, whereas in the study area mainly sand seems to be

transported. Additionally this phenomena could not bee observed during the field

work and must happened in the past or is only occurring temporarily. Studies of

Bhongsuwan and Auisui (2015) found out, that the mud near the hot spring A is

radioactive and also the water shows a high concentration of Ra-226 (Jeasai et al.,

2011).

A hard carbonate crust can be found in the surrounding at the hot spring in the

A-area. Cylindrical, vertical openings with a diameter till 10 cm pierce this crust

and indicate a way, where water was flowing in the past. The temperature in this

holes is still higher than outside, which suggests the existence of hot water under

15

the crust.

A different carbonate structure occurs at he springs in the B−, E− and F−area.

Carbonate is depositing on algae and can be found on the water surface and as part

of the soil. At the algae, the carbonate has a thin shape, whereas at the D-area also

thin vertical fibres have been found under the layered part (Figure 4.3).

Figure 4.3.: carbonate in the study area, left: E-area, middle: F-area, right: A-area

4.2. Aim of study

This study is using 1-D and 2-D geoelectical measurements for analysing the sub-

surface with regards to water reservoirs and upflow structures of the hot water.

Additional information of water and soil samples will be discussed in this context.

All the collected information will be considered for developing a model of the sub-

surface.

16

5. Methods

5.1. Sampling

Water samples have been taken from five hot springs in the study area and two at

a hot spring and its pool next to Chaiya City. At each place the water temperature

has been measured as close to the original spring as possible. It will be assumed,

that an error of ± 0.5 °C can occur per reading due to human inaccuracy.

All plastic bottles have been cleaned twice with the hot spring water before sam-

pling to minimize the effect of contamination through different water. The samples

have been analysed by the Central Equipment Division of the Prince of Songkla

University. Furthermore the salinity was measured in every sample with the Master

S28M (Atago) refractometer. Therefore a drop of the water was put on the glass

plate and the salinity could be seen at the scale. The refractometer is calibrated

for a temperature of 20 °C. Due to the fact, that the temperature while measuring

was higher and it is possible, that inaccuracies occured during the measurement, an

error of 0.1% should be considered.

Soil samples have been collected in different parts of the study area, including sam-

ples of the carbonate crust (SRT-A3 and A4) and precipitated mineral at the Chaiya

hot spring (STR-C). Additionally rocks have been sampled in two nearby quarries.

Some soil samples with a higher water content were carried in a plastic box, while

all of the other were stored in plastic bags.

After they were photographed and described, they were analysed with the X-ray

diffraction method.

5.2. Geoelectrical fieldwork

Four different survey lines have been investigated by three 1-D surveys and three 2-

D surveys in the study area. The positions of the lines were discussed in advance in

order to get meaningful data. Therefore geological maps and Google Earth pictures

have been used. In a geological survey, the feasibility of measurements at this lines

has been explored, pictures of the surrounding have been taken and quarrys in the

17

Figure 5.1.: Map of the different survey lines in the study area

nearby area have been visited.

In order to see the upflow structure in the subsurface, the majority of the survey

lines are crossing the trend of the springs.

The instrument ”DC Terrameter ABEM SAS1000” was used for all the geoelectric

measurements. We always measured at a straight line and at every electrode position

the resistivity was measured at least two times. When a high error occured, or the

difference between the results was high, it was measured again. Normally the error of

the instrument was smaller than 5%, but due to the low resistivity in the subsurface,

the error increased at some points to around 30%. Metal electrodes with a length of

30 cm were used. The coordinates were measured with the GARMIN etrex handheld

by an accuracy of 2 m.

5.2.1. 1-D measurements

1-D measurements were carried out at the survey lines 1, 2 and 3 (Figure 5.1). For

the vertical soundings (VES) the Schlumberger array was used. The main parame-

ter of each survey line, like the maximum AB/2 and the midpoint coordinates are

shown in Table 5.1. The reasons for using the Schlumberger array are the high depth

of investigation and the easy implementation in the field (Loke, 2015). As explained

18

in Chapter 2.2 the midpoint of the array is constant and the distance of the current

electrodes A and B is increasing logarithmically. To ensure a good signal strength

despite a high geometry-factor, the power electrodes are also increasing their dis-

tance to the midpoint. When the power electrodes are moved, two measurements

will be done with the same position of the current electrodes. One measurement

before and one after the movement of the potential electrodes. With this method

differences of the resistivity caused by the new electrode positions can be recognized

and reduced.

Table 5.1.: survey lines measured with the Schlumberger array

Line max. AB/2 /m direction midpoint UTM

VES 1 200 N-S 47P 0522010 E, 1032070 NVES 2 50 NW-SE 47P 0522070 E, 1031780 NVES 3 200 N-S 47P 0522187 E, 1032019 N

After the measurements the data were processed with the software RES1D (Loke,

2001) and IPI2Win (Bobachev et al., 2003). Therefore bad data points were reduced

and different models were developed. Only the most plausible model will be shown

in the results, but it has to be considererd, that the ambiguity can not be finally

solved.


Dipole-dipole arrays were used for the 2-D measurements at the survey lines 1, 3

and 4. This array is very sensitive to lateral changes and is thus a good possibility to

prospect vertical structures. Depending on the results of the vertical sounding the

spacings for the different survey line have been chosen. The spacing a and the total

length L of each survey line is shown in Table 5.2 together with their coordinates.

The aim for the measurement at line 1 (Dipole 1) was to get deep data and to

provide a good resolution. Because of the expectation, that the upflow structure

is bigger than a few meters, also a resolution of a several meters was acceptable.

Thus, a = 20 m was used. At line 3 the deeper subsurface should be explored and

the spacing was set to a = 25 m. The maximal length of line 4 was limited to around

110 m, so the aim was to get more information about the shallow subsurface and the

hot water under the carbonate crust. Therefore the spacing a = 5 m was chosen.

It was planned to use n = 8 for all measurements, because a higher value of n

increases the depth of investigation. But on line 3 only n = 6 was possible, due to

19

the low resistivity in the subsurface.

To minimize the movement of the electrodes, the measurements started with n = 1

until n = 8. Then, instead of moving the potential electrodes back and beginning

with n = 1 again, the first measurement with the new current position started with

n = 8. As seen in Figure 5.2, then the distance between the power and the current

electrodes were decreased till n = 1.

Figure 5.2.: Scheme of the dipole-dipole measurment in the field

Table 5.2.: Survey lines measured with the dipole-dipole array

Line a /m L /m max. n direction coordinates

Dipole 1 20 380 8 S-N 100 m: 47P 0522007 E, 1031971 NDipole 3 25 250 6 S-N 200 m: 47P 0522187 E, 1032019 NDipole 4 5 95 8 N 250 E 0 m: 47P 0522055 E, 1031805 N

The inversion was carried out with the software program Res2dinvx32 (Loke, 2003).

Due to lateral changes near the surface, the electrode spacing was set for the inversion

to the half of the original one. The software needs at least 20 datapoints. For line 3

only 18 could be measured, so two additional datapoints were added by considering

the measured data from the dipole-dipole line and the vertical sounding.

The software is generating a model of the subsurface and calculating the apparent

resistivity of this model. With the least-squares method the parameters of the model

will be changed, that the calculated data and the measured data are as similar as

possible.

20

6. Results

6.1. Samples

The temperature measurements in the field show that the water of all hot springs

is hotter than 55 °C. The water samples of SRT-A till E are all in the range of

61 °C - 68 °C, while the temperature of the water sample SRT-F is lower (56 °C).

The coordinates of the water samples and their temperature are shown in Table 6.1.

The parameters of the different hot spring water samples show many similarities. In

Table 6.1.: Coordinates, temperature and salinity of the watersamples

sample UTM N /m UTM E /m temperature /°C salinity /%

SRT-A 1031836 47P 522142 62 1.1SRT-B 1031935 47P 522067 65 1.1SRT-C 1035179 47P 520620 68.5 1.1SRT-D 1031660 47P 522310 61.5 1.1SRT-E 1031681 47P 522253 66 1.1SRT-F 1031490 47P 522320 56 1.1

each sample the pH-value is close to 7 and the resistivity is varying between 56 and

60Ωcm. The sodium concentration of around 3120 mg

lexplains the high salinity of

1.1%. The average value for the salinity in ocean water is 3.5% referring to Pond

and Pickard (2013). The distance between the ocean and the study area is with its

2 km relatively small and an influx of the ocean water in the water aquifers must be

considered.

With the parameters of the samples, the temperature of the reservoir can be es-

timated. The two main methods have been discussed in the chapter 2 and the

reservoir temperature was calculated with the silica geothermometer for no steam

loss (ref. equation 3.8). With the average amount of silica for the six hot springs

the reservoir temperature is 78.3 °C. Assuming a standard geothermal gradient of

30 Kkm

and a temperature of 25 °C at the surface, the depth of the reservoir can be

calculated. With Equation 3.10 the reservoir is situated 1.8 km under the surface.

The results of the XRD analysis mostly confirm the assumptions of the geological

21

survey. Carbonate can be found in the A-area as a hard duricrust on the surface

and as slices in the F-area deposited on algae in the hot pool. In the F-area you

can find in the topsoil a vertical carbonate structure connected with a horizontal

structure (Figure 4.3). The vertical fibres are very thin and easy to break. The

analysis showed, that at this sample halit can be found. This confirms the high

salinity value in the water. At this sample (right picture of Figure 4.3) a white

mineral can be found, which mainly consists out of calcite. Also the white mineral

found in area C seems to be precipitated calcite. In the A-area next to the spring

a soft and black material has been found. The material seems to be clay, due to a

grain size smaller than 0.002 mm. The XRD showed, that there is quartz, kaolinite,

illite and calcium aluminium silicate inside. But those ingredients do not explain the

dark black colour, so an other method should be additionally used. An interesting

Figure 6.1.: left: black clay in the B-area, right: mineral in a nearby sandstonequarry

sample has been taken in a nearby sandstone-quarry (1031543 N, 47P 521666 E)

and it is shown in Figure 6.1. It’s a composition of fluorite, kaolinite, anhydrite and

gypsum.

6.2. Geoelectric surveys


The resistivity value in the subsurface is low in the complete study area.

In Figure 6.2 the inversion result of the measured data at line 1 is shown for a

4-layer model. The high RMS error of 11.59% is probably the result of the difficult

measuring condition due to the low resistivity. All the different layers of the model

have a lower resistivity than 50Ωm. The layer with the highest resistivity (47Ωm)

can be found near the surface and is followed by a low resistivity layer (0.75Ωm)

with a thickness of only 20 cm. The resistivity of the next layer is slightly higher

22

and this layer reaches a depth of 13.5 m. The last layer has a resistivity of 25Ωm.

The exact parameters of the model are shown in Table 6.2.

In comparison to line 1 and 3 form the measured data on line 2 a smooth curve

Figure 6.2.: Model of VES 1 with 4 layers

(Figure 6.3). As a result the RMS-error is with 3.15% significantly lower. The

introduced model consists of 5 layers. The first layer is similar to the first one at

line 1, but it is followed by a small layer with a high resistivity (119Ωm). The

resistivity is decreasing at the third (12.8Ωm) and the fourth layer (5.23Ωm) till it

is increasing in a depth of 28.3 m again to 393.5Ωm. Thus, the resistivity at line 2

seems to be a slightly higher in the shallow subsurface than at the other two lines.

For the inversion of the data from survey line 3 a 3-layer model is used. The results

show, that the resistivity-values at this line are the lowest in the study area.

The surface layer has a resistivity of 4.6Ωm and a thickness of around 70 cm. The

resistivity is decreasing to the next layer (2Ωm) till it is increasing in a depth of 15 m

again to 13.4Ωm. In Figure 6.4 the results are shown and it can be recognized, that

the measured datapoints don’t form a smooth curve, which explains the RMS-error

of 12.41%.


In this chapter only the inversion models will be shown. For the figures of the real

data and the calculated apparent resistivity on base of the model, please refer to

23


Table 6.2.: Inversion results of the vertical soundings. Given are the depth z andthe resistivity ρ of the different layer

Line VES 1 VES 2 VES 3Layer z/m | ρ/Ωm z/m | ρ/Ωm z/m | ρ/Ωm

1 0 | 47.34 0 | 38.12 0 | 4.642 0.39 | 0.75 0.46 | 119.08 0.74 | 1.943 0.59 | 2.08 0.97 | 12.79 14.99 | 13.394 13.45 | 25.33 3.89 | 5.235 28.32 | 393.47

the appendix (Figures A.1- A.3).

Figure 6.5 show the inverted model of the data from line 1. The start point

of the line (x =0 m) is the southest point next to the mountain. Low resistivity

(<4Ωm) can be found till a depth of 15-20 m. The resistivity is in this top layer

in the south higher than in the north, but the difference is with around 3Ωm very

small. At a depth of 20-25 m the resistivity is then increasing. In this depth we see

a high resistivity region (around 18-27Ωm) between the line coordinate x =110 m

and x =160 m. The difference to the resistivity in the north of this region is bigger

than the one to the south. In the middle part of the line (170 m <x < 250 m) the

resistivity is 8Ωm. Towards the end of the section the resistivity is increasing again

and the higher resistivity layers seems to trend in the direction to the surface.

Also at line 3 there is a high resistivity region trending at the the north of the

24


Figure 6.5.: Inversion result of the dipole-dipole measurement at line 1

survey line towards the surface (Figure 6.6). Resistivities of more than 50Ωm can

be found there. Further to the south, the resistivity seems to change only vertical

and is increasing with the depth. While at around a depth of 50 m the resistivity

is higher than 26Ωm, the resistivity at 30 m is only 3Ωm. The resistivity closer to

the surface is even lower. Thus, it was difficult to carry out the measurements and

that is also a reason for the high error of the model (44.8%). In general it shares a

lot of similarities with the model of line 1, especially the low resisitivity region till

a depth of 25-30 m and the trend of the resistivity at the north of the lines.

The focus of the measurement at line 4 was the shallow subsurface. In Figure 6.7 a

model of the subsurface until a depth of 13 m is shown. In comparison to the other

two models, more changes in the resistivity can be seen at line 4. At the bottom

of the model, in a depth of 11-13 m the resistivity is around 15-20Ωm. In general

the resistivity is towards south west (start of the survey line) lower than towards

25



north east. Looking at the details of the model, the two low resistivity areas can

be recognized. One with a shape of a circle can be found at line coordinates 23 m

<x< 33 m. The second one is bigger and deeper (≈7 m) and is situated at 40 m till

55 m. The resistivity at the bigger one is lower (>0.2Ωm), but a closer look to the

scale shows, that the differences between them is very small. There is also a low

resistivity area (around 2Ωm) connecting the two anomalies and trending to the

surface. Next to the smaller anomaly a vertical low resistivity structure can be seen

at 22 m.

High resistivity areas can be found at x = 52.5 m with a resistivity above 30Ωm

and at x = 45 m with 15-20Ωm. The one with the higher values is directly at the

surface, while the second one can be found in a depth of 3 m.

The inversion error is for this model wit 46.7% very high, which can be a result of

the small changes in the resistivity and their low values.

26

7. Discussion

The geothermometer results with using the silica method are showing a reservoir

temperature of around 80°C. Results of the cation-geothermometer were significantly

higher (≈190°C), but this method is more vulnerable to other influences. Especially

the high sodium content as a result of interaction between groundwater and ocean

water contradicts the assumption of equilibrium of the reservoir and hot spring

water. Thus, the results of the silica method will be used. By combining the

geothermometer results and a normal geothermal gradient it could be seen that the

hot spring water is coming from a depth of over one kilometre. Even the calculation

with the standard geothermal gradient is not exact, a deep reservoir can be assumed.

For that, there must be a pass way for the upflowing water. Due to the fact, that

all springs form a trend line leading NW-SE, a regional geological structure seems

to enable the waterflow.

In the southern Thailand region there are two major strike-slip faults (Khlong Marui

and Ranong Fault) leading NNE, which have been discussed i.a. by Watkinson et al.

(2008). It can be assumed that a minor fault developed perpendicular to the both

major faults in the Chaiya District, due to the stress ratio in the subsurface.

Khawtawan et al. (2004) carried out gravity measurements in the Chaiya region.

They found a positive bouger anomaly trending NW-SE which they explain with

a normal fault system bringing limestone up towards the surface. The spring A in

the study area and spring C next to the limestone mountain near Chaiya are both

situated at the east side of this anomaly.

All these data suggest the existence of a extending fault, which enables upflow of

the water from the reservoir to the surface.

Similar parameters of the water samples could be found, which indicates that the

water is coming from one source. This statement is additionally supported by the

work of Jeasai et al. (2011). They measured the radioactivity of different wells and

hot springs, inter alia spring A and spring C. They both showed a high concentration

of Ra-226 in comparison to another hot spring near Chaiya, which was not part of

the recent study. This additional hot spring is situated on the west side of the

bouger anomaly and is probably not connected with the other hot springs.

27

The low resistivity data of the 2-D surveys at line 1 and 3 suggest a water saturated

soil with a high clay content until a depth of 25-30 m. Under this layer the resistivity

is increasing and it is possible that this shows a transitional region between the clay

and the hardrock. For hardrock the resistivity is with 40-50Ωm still low, but can be

explained by a high water content. It is also likely that the resistivity will increase in

higher depths. Due to the existence of the sandstone mountain and the sand, found

in the shallow subsurface, the hardrock seems to be sandstone. The occurrence of

sandstone in the depth could be part of the explanation of the sand transport of the

hot springs. Hot water is moving up through the sandstone and taking small sand

particles to the surface.

With the 2-D data of line 1 and 3 it can be recognized, that the high resistivity region

is trending towards the surface in the north. This trend can also be seen in the data

of the vertical sounding of line 3, which midpoint is situated at line coordinate x =

200 m in the the model (Figure 6.6) of the dipole-dipole measurement. There the

low resistivity layer can be already found in a depth of 15 m. Due to the fact, that

the VES is additionally influenced by the north part of the survey line, which is

not shown in the dipole section, the rising of the high resistivity layer seems to be

possible.

A look on the map shows, that the position of this structure is in line with the general

trend of the hot springs. Thus is possible, that the fault enabled a movement of the

layers in the past.

By combining all this information the subsurface model shown in Figure 7.1 can be

developed. Next to the surface the clay layer can be found and in the depth the

sandstone. A vertical displacement of the layers can be found in line of the hot

springs and along this line.

Unexpected is the result, that even next to the sandstone mountain (VES 2) the

sandstone can only be found deeper than 20 m. This observation fits to the steep

slope of the mountain and indicates a nearly vertical boundary. In the model of the

dipole-dipole measurements a 80 m low resistivity area at 170 m <x < 250 m can

be seen in a depth of 20-50 m. It is possible, that the low resistivity is caused by a

higher water content, then the surrounding. This leads to the assumption, that this

area is part of the upflow structure of the water (refer to Figure 7.1).

The measurements on line 4 allow a closer look to the shallow subsurface. The two

low resistivity areas can be interpreted as two shallow hot water reservoirs. Due

to the fact, that the information is limited on two dimensions, it is possible that

the reservoirs are lateral connected. Next to the x =40 m an additional hot pool

can be found 5-10 m towards south. It is bordered by concrete walls, but maybe

28

Figure 7.1.: Model of the subsurface in the study area

underneath connected with the two reservoirs. The assumption that the water in

the reservoirs is hot, is based on the hot spring nearby and the high temperature in

the holes piercing the carbonate crust.

The high resistivity areas are probably linked with a less water content of the soil

or the carbonate crust. Also an influence of the humans building the walkway is

possible.

Further research should be done on the transport mechanism of the sand and its

time depended occurrence. Also the formation process of the carbonate structures

should analysed. Measurements with different methods and data from a nearby

drilling hole could provide important data for a more detailed model.

29

8. Conclusion

The study area in the north of the Surat Thani province shows signs of a fault ,

which enables the upflow of the hot water in this regions. The fault line is trending

NW-SE and thus it situated perpendicular to the Khlong Marui fault.

Watersamples and Ra-226 measurements by Jeasai et al. (2011) suggest, that there

is one source for the different hot springs with a temperature of around 80°C. The

assuming the standard geothermal gradient, the reservoir can be found in a depth

of 1.8 km.

Figure 7.1 shows the model of the subsurface with two main layers. Hard rock

(sandstone) can be found in a depth of 20-30 m and this layer is probably the source

of the sand, which is transported by the hot water. On the top a clay layer can be

found, which is in many parts water saturated resulting a low resistivity (1-6Ωm).

A vertical displacement of the layers can bee seen along the survey line and there is

also the water flowing up. In the shallow subsurface small hot water reservoirs can

be found under the carbonate crust.

30

9. Acknowledgements

Ich möchte mich beim DAAD und vor allem bei den Organisatoren des RISE-

weltweit Programms für die Unterstützung und natürlich das Stipendium bedanken!

Ein weiteres Dankeschön geht an Dr. Ellen Gottschämmer, die mir mit Ihrem

Empfehlungschreiben eine Teilnahme ermöglicht hat.

I would like to thank all the people I could work with during my project, especially

my supervisor Asst. Prof. Dr. Helmut Duerrast. He supported me before and

during this project and helped me with questions about the organisation of my stay

as well as scientific topics.

31

Bibliography

Berckhemer, H. (1990). Grundlagen der Geophysik. Wissenschaftliche Buchge-

sellschaft, Darmstadt.

Bhongsuwan, T. and Auisui, S. (2015). A high natural radiation area in khao-than

hot spring, southern thailand. Radiation protection dosimetry, 167(1-3):284–288.

Bobachev, A., Modin, I., and Shevinin, V. (2003). Ipi2win vers. 2.0: User’s guide.

Geological Faculty, Dept of Geophysics, Moscow State University.

Dimitrov, L. (2002). Mud volcanoes—the most important pathway for degassing

deeply buried sediments. Earth-Science Reviews, 59(1):49–76.

Fournier, R. (1977). Chemical geothermometers and mixing models for geothermal

systems. Geothermics, 5(1-4):41–50.

Fournier, R. (1989). Lectures on geochemical interpretation of hydrothermal waters.

UNU Geothermal Training Programme.

Imagery, N. and Thailand’, M. A. (2000). Amphoe Chaiya 1:50000. L7018. Royal

Thai Survey Department, 1-rtsd edition.

Jeasai, S., Bhongsuwan, T., and Chittrakarn, T. (2011). Specific activity of ra-226

in water from hot springs and nearby shallow wells in suratthani province.

Khawtawan, A., Lohawijarn, W., and Tonnayopas, W. (2004). Gravity anomaly of

chaiya geothermal area. Proceedings of the International Conference of Applied

Geophysics in Chiang Mai.

Loke, M. (2001). Res1d version 1.0. 1-d resistivity, ip & sip inversion and forward

modeling. Wenner and Schlumberger arrays. User’s Manual.

Loke, M. (2003). Rapid 2d resistivity & ip inversion using the least-squares method.

Geotomo Software, Manual, 122.

Loke, M. (2015). Tutorial : 2-d and 3-d electrical imaging surveys.

32

Lowrie, W. (2006). Fundamentals of geophysics. Cambridge University Press, Cam-

bridge, 1. publ., 7. print edition.

McGillivray, P. and Oldenburg, D. (1990). Methods for calculating fréchet deriva-

tives and sensitivities for the non-linear inverse problem: A comparative study1.

Geophysical Prospecting, 38(5):499–524.

Pond, S. and Pickard, G. (2013). Introductory dynamical oceanography. Elsevier.

Watkinson, I., Elders, C., and Hall, R. (2008). The kinematic history of the kh-

long marui and ranong faults, southern thailand. Journal of Structural Geology,

30(12):1554–1571.

33

A. Appendix

A.1. 2-D measurements

Dipole 1

Figure A.1.: Measured apparent resistivity (top), Model of the resistivity (bottom)and calculated apparent resistivity (middle) of this model at line 1

i

Dipole 3


Dipole 4


ii

Table A.1.: Chemical analyse of the water samples

SRT-C SRT-CC SRT-B SRT-A SRT-E SRT-D SRT-F

pH 6.95 7.24 6.86 6.83 6.9 7.63 7.27Fe in mg/L 0.004 0.001 0.001 0.002 0.056 0.003Mn in mg/L 0.02 0.02 0.01 0.01 < 0.01 < 0.01Ca in mg/L 714 393 703.5 690.25 703 716 711.75Mg in mg/L 112.98 129.3 107.5 108.37 106.68 109.93 111.3Na in mg/L 3172.5 2537 3045 3112.5 3065 3125 3215K in mg/L 313 577.7 295.5 295.25 297 297.5 297.25Cu in mg/L not detected not detected not detected not detected not detected not detectedZn in mg/L 0.004 0.005 0.004 0.003 0.003 0.003SO4 in mg/L 512 624 547 626 619 600Cl in mg/L 6259.98 1646.8 6458.2 6558.31 6758.5 7508.25 6608.36F in mg/L 1.1 1.3 1.6 1 1.6 2CO3 in mg/L not detected not detected not detected not detected not detected not detectedHCO3 in mg/L 206.22 206.22 171.85 171.85 206.22 171.85NO2 in mg/L 0.04 0.04 0.03 0.04 0.04 0.06NO3 in mg/L 3.99 1.33 0.44 not detected 2.66 0.89total hardness in mg/L 2136 1993.6 2066.7 2314 1958 2036Noncarbonate hardness in mg/L 637.5 650 569.77 652.07 644.77 625TDS in mg/L 9620 8970 10060 10080 10030 9970 9510Pb in mg/L 0.026 0.029 0.028 0.025 0.025 0.029Ba in mg/L 0.092 0.089 0.088 0.086 0.087 0.089Resistivity in Ohm cm 59.98 58.11 57.87 58.28 56.72 56.15Silica in mg/L 27.08 39.95 31.87 27.03 23.65 28.35

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