Hydrogeochemical Characteristics of Geothermal Water in Mount Lawu, Indonesia

Abstract

Mount Lawu is a stratovolcano located in the border of Central and East Java province, Indonesia. Mount Lawu holds a vast potential of geothermal energy indicated by widely distributed thermal manifestations. This study aims to evaluate the hydrogeochemical characteristics on the western side of Mount Lawu and also to create a simple preliminary hydrogeochemical model based on geological and geochemical data. Surface manifestations showed all types of chloride, sulphate and carbonate water are present among both hot and cold fluid chemistry with pH ranging from 1-2 and 6-7 on the central and proximal facies of Mount Lawu respectively. Isotopic analysis of thermal water indicates both magmatic water and meteoric water that circulates within Mount Lawu geothermal system. Fe and As concentrations appear to be higher in some manifestations indicating intense rock-fluid interaction from the reservoir to the surface. Moreover, Na/K geothermometer indicates an intermediate-high enthalpy system. Based on these findings, a hydrogeochemical model was synthesized and also proved that Mount Lawu is a volcanic geothermal system with intermediate-high enthalpy energy.