Physical and Chemical Characteristic of Geothermal Manifestation in Telagabodas, West Java, Indonesia

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1 Physical and Chemical Characteristic of Geothermal Manifestation in Telagabodas, West Java, Indonesia Azy, F.N. 1, Jihadi, L.H 1, Darana, A.R 1, and Oscar A.W. 1 1 Faculty of Geological Engineering, Universitas Padjadjaran, Jalan Raya Bandung Sumedang KM 21, 45363, Bandung, Indonesia fikri11007@student.unpad.ac.id Keywords: Characteristic, geothermal, Telagabodas, geochemical, hotspring ABSTRACT Geothermal energy provides a great amount of energy and cleaner than fossil fuel usage, so it could be and alternative to fossil fuel. In a country with many volcanic activities, such as Indonesia, geothermal potential is very high. One of the area in Indonesia which has the potential located in Telagabodas, West Java. The geological and geochemical approach is used to determine the characteristic of the geothermal manifestation. The manifestations in Telagabodas are indicated by mudpool, solfatara, and hotspring. The data, taken from the chemical measurement, represent the presence of Na, K, Mg, Cl, SO 4, and HCO 3. Based on the chemical data, as well as physical data i.e.: ph, TDS, and EC, our analysis shows that the characteristic of geothermal manifestation is assumed as immature. The condition is indicating that the water in geothermal system is mixed or the geothermal system has a shallow ground water. 1. INTRODUCTION 1.1 Background Fossil fuel has become a main energy source to fulfill energy demand. However, excessive fossil fuel usage is depleting the resources. Therefore, an alternative way to obtain energy source is needed. Geothermal energy could be the solution, because it provides a great amount of energy and cleaner than fossil fuel usage. In a country with many volcanic activities, such as Indonesia, geothermal potential is very high. Indonesia is located in a giant subduction zone where three mayor plates collide. The subduction zone is formed by the collision of Eurasia Plate, Australia Plate, and Pacific Plate. Eurasia Plate and the Pacific Plate crashed in the northeast of Indonesia, while Eurasia Plate crashed with Pacific Plate and Australia mostly in the southern part of Indonesia. As a result Indonesia s tectonic structure is very complex especially the structure along the collision zone which includes Fore Arc, Volcanic Arc and Back Arc. So there are a lot of volcanoes that very potential for the geothermal resources. One of a place that could have a geothermal potential is located at Telagabodas, West Java, Indonesia. The Telagabodas area shows some manifestations of geothermal activity such as solfatara, fumarole, mud pool, and hot spring. Because of that, the area has a posibbility to be a geothermal energy resource. Before the exploitation is done, the geothermal potential should be determined first, that is why geothermal exploration is needed. Geothermal exploration, including geological and geochemical analysis, can reassure the potential possibility at Telagabodas Area. Through characteristics, both chemical and physical characteristic of water manifestation, reservoir properties such as its temperature, and fluid type could be predicted, after geological properties analysis is done. In this study, we focused in geological and geochemical analysis to determine geothermal area characteristic by measuring water composition taken from where the geothermic manifestation existed and geological properties such as, structures, volcanic stratigraphy, and rock types of research area. From the data, we can determine which type the reservoir is. Even though, in order to determine the geothermal potential, further analysis and exploration are needed. 1.2 Geological Condition The Research area, Mt. Telagabodas, is a volcanic mountain located in the north to southwest side of Mt. Galunggung. According to Budhitrisna (1986) in Geologic Map of Tasikmalaya Quadrangle, in the research area, around the crater of Mt. Telagabodas consists of rocks resulted from young volcanic mountain activity i.e.: volcanic breccia, laharic rocks, and tuff that composed by interspersed andesitic-basaltic rocks as the result of Mt. Telagabodas eruptions. Outcrops in the area show grayish andesitic rock and some rocks which are heavily altered. Petrografic test shows that the andesitic-basaltic rock type is categorized into andesitic pyroxene, also andesitic lava is found around the crater of Mt. Telagabodas (Irianto et al. 2000). Rocks that generated near the Mt. Telagabodas site consist of cycled sequence of lava and pyroclast that intercalated with each other as a result of eruption at varied spots. Based on Suhadi et al. (1999), those rocks are divided into 39 units, i.e.: A. Telagabodas Lava It composed by grayish brown into black andesiticbasaltic rock with porphyritic and massive texture. Also, it consists of pyroxene and plagioclase mineral, vesiculated in someplace also showed in outcrop as a boulder. B. Telagabodas Pyroclastic This unit is lightly browned, the state has weathered, solid, consisting of meterial sized volcanic ash to lapilli. It creates a bedding plane with thickness around 15 to 20 cm and 10 to 20 meters thick when exposed as an outcrop. C. Sadahurip Lava It is predicted as a product of side eruption when Mt. Telagabodas was erupted. It mainly has a shape of cone, isolated, forms andesitic-basaltic lava with porphyritic and massive texture. Also, it has a heavily weathered condition. D. Candramerta Lava Candramerta lava is generated by side eruption of Mt. Telagabodas. It consists of andesitic-basaltic rocks

2 with grayish to black color which texture is porphyritic, also with weathered condition E. Bungbulang Lava This unit is formed as the result of a volcanic eruption on the side of Mt. Telagabodas which form a cone shaped morphology. On the morphology, slope was developed to the east, following the slope of Mt. Telagabodas. In general, the rock is heavy weathered which color is weathered brown, while dark gray is the fresh color. It has a massive structure, and partially forms boulders or blocks of lava which were affected by geological structures such as faults. F. Malang Lava This unit is mostly covered Bungbulang Lava and suspected as the result of the side eruption Telaga Bodas. It spreads around the east to northeast Mt. Telagabodas in a cone-shaped appearance. At a certain height, the rock has a dark gray color with porphyritic texture. G. Lebakjero Lava In general, this unit forms andesitic-basaltic lava which is gray-black with porphyritic and massive texture. Also some minerals pyroxene and plagioclase can be found in this unit, and in some places there are traces of solfatara. H. Lebakjero Pyroclastic Flow This unit is a result of pyroclastic flows, apparently with brown to reddish appearance. It is composed by andesitic-basaltic components which size are between pebbles to boulders, also composed by lytic components of an average diameter 3-5 cm which is poorly sorted and sub-angular shaped. I. Lebakjero Pyroclastic Fall This unit is can be found on the western slopes of Mt. Telagabodas. It covered cover most Lebakjero Pyroclastic Flow and Telagabodas Lava which color is brown to blackish, and composed by volcanic material which size is ash to lapilli. J. Masigit Lava Masigit Lava spreads around Masigit Crater, constructing wall and floor of the crater. The cooled down lava creates andesitic-basaltic rocks which is blackish gray, weathered and altered by solfatara.. K. Patrol Lava Dome This unit located at the north of Mt. Telagabodas, spreads along and creates dome morphology which is very rounded. It composed with andesitic-basaltic lava rocks which are blackish gray with porphyritic texture. L. Tegalsaat Piroclastic Fall This unit spreads along northwest side of Patrol Lava Dome and creates cone-shaped morphology. It composed by foliated blackish gray ash-lapilli volcanic rocks. M. Masigit Piroclastic Fall Masigit Pyroclastic Fall covers a part of Lebakrejo Lava unit. It has brownish black appearance which composed by ash, sand, and lapilli bedding. N. Masigit Pyroclastic Flow This unit covers Masigit Pyroclastic Fall. It composed by yellowish weathered and altered andesitic-basaltic igneous rock. O. Lahar (Lh) This unit located near the northeast side of the foot of Mt. Telagabodas with a rather flat landscape that is used by people for farming or rice fields. It composed by ash, sand and igneous components, poorly sorted and weathered. According to Suhadi, D et al. (1999), structurally, there is a few of structure that developed or had been generated in the area near Mt. Telagabodas, i.e.: Candramerta Fault, Sadahurip Fault, Bungbulang Fault, Pasir Sigung Fault, Cibodas Fault, and Ciparay Fault. Also there is some structure in main crater. These structural faults occurrence is resulting in geothermal manifestation around the study area, including fissure at groundwater aquifer that resulting in hotsprings to occur. 2. METHOD This research is done in refer to Zakaria (2013) geological mapping procedure. Based on remote sensing, mapping track is prepared, so all required spatial data can be taken. The spatial data are taken based on their locality, and the locality has to represent the area. The spatial data includes geological and morphological aspects that will be used to describe and relate each locality properties. Hotsprings described in geological aspect. The physical properties of water on the hotsprings measured using multi-tester water device, while chemical properties are measured in a lab. The water samples are taken at each hotsprings that spread along the study area, using labeled plastic bottles. After that, all of the data is analyzed and discussed based on its geochemistry aspect in order to describe the characteristic of geothermal manifestation in the study area. 3. RESULT AND DISCUSSION 3.1 Geothermal Manifestation One of the geothermal manifestations that can be found around the crater of Mt. Telagabodas is a mud pool that located alongside of the crater, exactly at the east side of the crater. The mud pool has diameter of 1.5 meter with very active hot mud that comes out from underground (Fig ). Alongside the mud pool, 5 to 8 meter from it, amd active fumaroles with sulfuric gases can be identified and estimated as solfatara. The solfataras produces very thick sulfuric gases, that abundant enough to make human hard to breathe. Hotspring site that is sampled, Telagabodas-2 (Tlb-2), located near the mud pool and solfataras. The hotspring produces bubbles, which water characteristic is very acid (Table and Table 3.2.2). Another hotspring near the Tlb-2, the south side from Tlb-2, is already been used as a bath area by locals, a sample also taken here and labeled as Telagabodas-1 (Tlb-1). Around the Tlb-1, many outcrops show heavily altered andesitic-basaltic rocks.

3 Fig Telagabodas Geological Map

4 Fig Geothermal manifestation, shows an appearance of mud pool with solfatara on its side Sample is taken at the site, close to where the bubbles come from. B. Cikajayan Hotspring It located at the end of public local bath, southern side of Cienggang hotspring. The hotspring forms a warm water river. In this hotspring also has a sulfuric smell, but the smell is not as bad as Cienggang hotspring. Some bubbles can be found in the hotspring with yellowish residue. C. Ciateul Hotspring Ciateul Hotspring can be found between Cienggang and Cikajayaan hotspring. Here, greenish residue accumulated below the water. Bubbles are comes out to the surface alongside with steam. 3.2 Water Characteristic Other sites which water is sampled located around hotspring area, at the eastern side, 1 km from Mt. Telagabodas crater. Also this hotspring area has been used as public bath by locals, those hotspring area are: A. Cienggang Hotspring It located near access road that connects Telagabodas area with Tasikmalaya city. The hotspring produces sulfuric bubbles, assumed from the sulfuric smell and withered residue that can be seen below the water. Water characteristic can be divided into chemical characteristic and physical characteristic. Physical characteristic is measured on the field. The measurement includes ph, temperature, and TDS/EC measurement. Chemical characteristic is measured at lab, in order to determine chemical composition such as Na, K, Mg, Cl, SO 4, and HCO 3. The results of measurement, both physical and chemical properties measurement can be seen at the table (Table and Table 3.2.2). Tabel 3.2.1, Chemical characteristics measurement result Telagabodas 1 (Tlb-1) Telagabodas 2 (Tlb-2) Cienggang (Tlb-3) Cikajayan (Tlb-4) Ciateul (Tlb-5) Element (mg/l) S S S S S E E E E E '27.0 Na K Mg 11,6 8,7 23,5 34,9 14,3 <0,1 <0,1 2,0 20,3 1,1 20,4 29,0 60,0 75,4 31,6 Cl 67,5 312,5 274,2 407,5 579,2 SO HCO 3 112,0 106,0 104,2 417,0 121,6

5 Table 3.2.2, Physical characteristics measurement result Telagabodas 1 (Tlb-1) Telagabodas 2 (Tlb-2) Cienggang (Tlb-3) Cikajayan (Tlb-4) Ciateul (Tlb-5) Physical Characteristic S S S S S E E E E E '27.0 ph 4,4 1,4 2,8 1,6 2,3 Temperature ( 0 c) 37,5 36,7 49,4 45,2 41,2 EC (μs/cm) TDS (mg/l) Analysis of Surface Geothermal Manifestation Geothermal manifestation occurs as a result of geothermal system activity below the surface. The geothermal system in general built by components such as fluids, heat source, and reservoir (Goff and Janik, 2000). The components which create the geothermal system also triggered rock alteration, as the high temperature magmatic and meteoric water breach into rock around the geothermal system. According to characteristic that can be seen on the field, geothermal manifestation in Telagabodas is a result of volcanogenetic geothermal system which is very affected by magmatic heat. Also, the manifestation could be affected by structural faults (Fig 3.2.1). There is a structural fault alongside the crater of Mt. Telagabodas. 3.4 Analysis of Physical and Chemical Characteristic Based on Nicholson (1993), temperature in the geothermal system can be predicted using geo-thermometer based on mineral in water and its chemical compound. The geo-thermometer can be applied into geothermal manifestation such as natural hotspring and also hotspring that comes out from drilling well. Geo-thermometer is based on mineral solubility (silica) and ion exchange reaction (Na-K, Na-K-Ca). Fluid in hotspring around the study area is very high in Mg, much higher than Na and K (Fig 3.4.1). The figure shows that water condition is immature. The condition means that the water in geothermal system could be mixed or that the geothermal system has a shallow groundwater. Generally, water type in hotspring can be classified as chloric (Cl), sulfate (SO 4 ), and bicarbonate (HCO 3 ) based on its relative comparison of Cl, SO 4, and HCO 3 anions. Chloric water is dominated by Cl anion with concentration exceed mg/kg (Nicholson, 1993). Chloric water manifestation usually occurs with greenish residue below the water. Sulfate water type is usually found in area which groundwater is near the surface (<100 m) and the manifestation could be found as a mud pool. The sulfate water resulted from oxidation reaction between H 2 S into H 2 SO 4. The bicarbonate water is dominated by HCO 3, resulting travertine residue near the surface if the Ca is high (Nicholson, 1993). Fig The diagram shows comparison between anions of chlorida (Cl), sulfate (SO 4 ), and bicarbonate (HCO 3 ), indicating water type in each site. Fig Relative comparison of Na K Mg of water in hotsprings around the study area shows that water condition is immature (Giggenbach, 1988 in Nicholson, 1993) According to the diagram (Fig 3.4.2), the study area has bicarbonate, chloride-sulfate-bicarbonate, chloride, and sulfate water type. Telagabodas-1 (Tlb-1) is bicarbonate with high concentration of HCO 3 anion, which is predicted as the seepage water that occurs around the

6 crater of Mt. Telagabodas. Telagabodas-2 (Tlb-2) and Ciateul (Tlb-5) is categorized as chloric water type which is dominated by Cl anion. Tlb-2 and Tlb-5 is assumed that the water comes from reservoir of the geothermal system, below the surface. Cienggang (Tlb-3) is categorized as sulfate water and it could be caused by oxidation reaction between H 2 S into H 2 SO 4 that occurs near the hotspring. The last sample Cikajayaan (Tlb-4) has an unique condition where all the anion (chloride-sulfate-bicarbonate) is nearly in balance, maybe it caused by mixed water in the surface as the sample is taken near a hot water river. 4. CONCLUSION The Telagabodas area has a volcanogenetic geothermal system based on its manifestiation, i.e.: mudpool, solfatara, and hotspring. According to the result of geological approach, the area contains altered andesiticbasaltic rock including andesitic pyroxene and piroclastics rocks, while the geochemical analysis shows that the characteristic of water in the manifestation is immature indicating that the water in geothermal system is mixed or the geothermal system has a shallow groundwater. ACKNOWLEDGEMENTS We really appreciate the help from Hidrogeology and Geo-environment Laboratory of Faculty of Engineering Geology and Physical Chemistry Laboratory of Faculty of Mathematics and Sciences, in University of Padjadjaran. Also, we are really grateful for the cooperation with Chemistry and Environment Laboratory of PT. Ubar Jalindo, supervised by Dr. Solihudin, And we really grateful for the support that given by Mr. Zufialdi Zakaria and Mr. Johannes Hutabarat, who kindly guide us in the process of this study. REFERENCES Budhitrisna T,: Geologic Map of Tasikmalaya Quadrangle, West Java, Geological Research and Development Center of Indonesia : Bandung. (1986) Irianto, Pribadi, A., Suherman, W., Tripambudi, A.S. : Laporan Penyelidikan Petrokimia Batuan Gunungapi Telaga Bodas, Jawa Barat, Badan Geologi : Bandung. (2000). Suhadi, D., Kusdaryanto, Mudjiman, Y., : Pemetaan Geologi Foto Gunungapi Telaga Bodas, Kabupaten Garut dan Tasikmalaya, Direktorat Vulkanologi : Bandung. (1999). Goff, F. and Janik, C.J, : Geothermal Systems. In Encyclopedia of Volcanoes (editor: Sirgudsson, H., Houghton, B., McNutt, S. R., Rymer, H., Stix, J.), Academic Press, San Diego. (2000) Nicholson, K., : Geothermal Fluids Chemistry and Exploration Techniques, Springer Verlag, Jerman. (1993) Zakaria Z : Management of Geological Mapping, 220 pp. Faculty of Geology, University of Padjadjaran: Jatinangor (2013)