Karakteristik Tanah Beruap di Kawah Domas, Tangkuban Perahu
Domas crater is located on the west flank of the Volcano Complex of Tangkuban Perahu. The crater is active indicating the occurrence of surface manifestation of steaming ground, steam vents and hot pools. A study was carried out in Domas crater to understand the characteristics of lithology, geological structure, alteration and others, e.g. temperature, pH and several elements. Geological and hydrothermal alteration mapping were done at the surface condition using 1:1000 scale. Field megascopic-observation and direct-measurement are the main method used in this research. Other methods include laboratory analysis of petrography, X-ray Diffraction (XRD), Scanning Electron Microscope with Energy Dispersive X-ray (SEM-EDX), and chemical analysis of Si, S, Al and Hg. Evolution of Domas crater was started as phreatic eruption occurred about 10,000 years ago. Product of the eruption is polymictic breccia, overlying andesite lava within northwest-southeast trend collapse-structure. Direction of the eruption is likely from west, i.e. close to the crater wall, to east. After the formation of polymictic breccia, lithology of Domas crater was dominated by, from old to young, crystal tuff, andesite breccia and the last of colluvial deposit, which is still forming now. As the phreatic eruption had occurred, steam from boiling of reservoir fluid ascended and condensed. Interaction between hydrothermal fluid and surrounded rocks causes alteration to occur. The alteration occurring in Domas crater is generally leaching and silicification and can be divided into silica-sulfur, weak to moderate silica and moderate to strong silica zones.
Thermal fluids from the hydrothermal volcanic system of Tangkuban Parahu is still present in Domas crater until now. It is shown by the occurrence of active manifestation of steaming ground, steam vents, boiling pools, warm to hot pools. Direct measurements of temperature and pH show that steaming ground of Domas crater has ground temperature of between 60 and 90oC and pH of between 1.25 and 3.63.
Dr. Eng Suryantini ST. Dipl. Geothermal Tech., M.Sc