Identification of Geothermal Prospect Zone in Ijen Caldera (East Java) Using Geomagnetic Method and Landsat Data Analysis.

Ijen Volcanic Complex (IVC) is located in the easternmost part of Java. This complex consist of three groups of volcanoes including the Old Ijen Caldera, Caldera Rim Volcanoes and Intra Caldera Volcanoes. The complex is expected to have geothermal system which is indicated by the occurrence of Blawan hotspring at the northern part of caldera rim and acid lake on Ijen Crater. The presence of surface manifestation is very rarely in this area. The Blawan hotspring represents typical outflow of geothermal system, while the existence of extremely acid lake on Ijen Crates indicates that the area should be avoided for geothermal development. Accordingly, the location of the geothermal system is still hidden and become a challenge to be explored. In order to identify the prospect zone of Blawan-Ijen geothermal area, a landsat data analysis and magnetic survey were conducted. From the landsat analysis, volcanoes and geological structures were delineated to understand the geological condition. Besides, a magnetic survey was also carried out in 2017 for 72 stations using aproximately 1 - 1.5 km grid spacing. The magnetic anomalies were processed using reduced to pole (RTP). The negative magnetic anomalies occur over the southeast part of the study area and also in the western part of the N-S structure. The negative anomaly in the southeast area is probably associated with the hydrothermal demagnetization. This is supported by landsat imagery that shows a volcanic feature right in that area. [ABSTRACT FROM AUTHOR]