Detection of Sinkhole Potential Using Very Low Frequency (VLF) Method: A Case Study in Kedungsalam Village, Malang Regency

Several caves and sinkholes in Kedungsalam Village, Malang Regency, indicate an intensive and active carbonate rock dissolution process beneath the surface. This condition poses a risk of subsidence disaster that could threaten the safety of residents. This study aims to determine the potential for subsidence using the Very Low Frequency (VLF) method. The VLF method detects the presence of cavities based on the conductivity properties of the rock. Data collection was carried out on four routes adapted to field conditions. Data processing was carried out using the Fraser Filter and Karous Hjlet. The interpretation results identified several zones with high conductivity values, indicating the presence of cavities that could cause soil structural instability. The interpretation results from line 1 showed four anomalies at distances of 20–50 m, 125–150 m, 230–250 m, and 410–440 m. Line 2 presented two anomalies at distances of 280–340 m and 450–500 m. Line 3 shows three anomalies that are likely cavities at distances of 95–125 m, 180–230 m, and 320–370 m. Line 4 shows four anomalies at distances of 80–150 m, 200–240 m, 350–400 m, and 450–480 m. The results of this study can be used to inform policymaking to mitigate the risk of land subsidence and ensure safe spatial planning.