INTEGRATION OF GEOPHYSICAL AND HYDROGEOCHEMICAL METHODS TO REVEAL THE KARST AQUIFER SYSTEM IN GEOTOURISM AREAS, LO AND BANGI CAVES, SOUTH MALANG, INDONESIA

Abstract

Karst areas have complex hydrogeological systems resulting from the dissolution of carbonate rocks, fracture networks, and the presence of underground rivers. Lo Cave and Bangi Cave, in South Malang, are located in the Wonosari Formation and are known as active underground river sites with potential for the development of karst geotourism, speleology, and water resources. However, to date, no study has combined geophysical and hydrochemical methods to provide information on underground river connectivity, karstification levels, and groundwater vulnerability at these sites. This study aims to understand the subsurface structure, flow patterns, and geochemical processes as a basis for geotourism development. This study was conducted in Kedungsalam Village, South Malang, Indonesia. This study used Self-Potential (SP), Induced Polarization (IP), and Hydrochemical analyses. SP data showed negative anomalies consistent with underground flow paths connecting the two caves. IP data identified loading zones at Lines 4, 6, and 7, which are suspected to be active cavities and water-filled channels. Hydrochemistry analysis showed that all samples had low mineralization (TDS 31-63 mg/L), neutral to slightly alkaline pH, and were dominated by Ca²⁺–Mg²⁺–HCO₃⁻ ions. Similar hydrochemical facies confirm that all water sources originate from a single, interconnected karst aquifer system. Integration of geophysical and hydrochemical methods reveals that Lo Cave and Bangi Cave form a hydrogeological system, with active channels and flow controlled by carbonate dissolution.