Surface Thermal Manifestation Mapping in Kamojang Geothermal Field, West Java, Indonesia

Abstract

Kamojang Geothermal Field is located in Bandung, West Java, Indonesia. Since 1978, this field has been producing electricity with total capacity about 235 MWe. Surface thermal manifestation monitoring is a powerful tool to monitor changes of reservoir condition. The investigation aimed at mapping new thermal manifestations and ground temperatures in Kamojang crater. The method employed is field mapping using drones and tracking. Ground temperatures were acquired directly in the field by measuring at 20 cm depth. Geologically, Kamojang Crater area is dominated by volcanic rocks such as andesite lava, pyroclastic breccia, tuff, and lapilli. It has undergone moderate to very strong alteration into clay, silica, iron oxide, and anhydrite minerals. The main geological structures that play a role in Kamojang area are Kendang, Patengteung, and Citeupeus Fault systems. Surface manifestations discharged in Kamojang area consist of mud pools/vents, hot springs/pools, steaming ground, and steam vents that are controlled by Citeupeus and Pateungteung Faults with a NE-SW orientation. The area was later referred to as Kamojang Crater, which consists of Manuk, Berecek, Sakarat, Kamojang, Kereta Api, Cikahuripan, Hujan, Loutak, Baru, Saar, and Inactive Craters. Several new hot spots have not been mapped in detail by previous research, including Timur Crater, Mud Pool Complex, and Tengah Crater. Meanwhile, an Inactive Crater to the north of study area indicates activity shown by boiling and bubbling hot pool. The thermal manifestation has a high temperature of 50.4 to 94.7°C. Manifestations in the form of liquids (mud and water) have an acidic fluid, with a pH ranging between 1.30 and 5.50. Ground temperatures in Kamojang Crater area range from 17 to 95°C. High temperature areas of 80 - 95oC are associated to thermal manifestations.