Investigating Landslides Induced by Hydrothermal Alteration Using Gravity and Magnetic Methods: A Case Study of Songgokerto, Indonesia

Songgokerto, a Batu City, Indonesia subdistrict, features diverse topographical variations dominated by mountainous and valley landscapes. According to the 2024 data from the Regional Disaster Management Agency (BPBD) of Batu City, landslides frequently occur along Trunojoyo Road in Songgokerto. This road serves as a major transportation route connecting several key cities in East Java, including Batu City, Malang Regency, Kediri City, and Jombang Regency. Landslides in this region often lead to complete road closures, disrupting economic activities and raising safety concerns for travelers. The economic stagnation caused by blocked road access poses significant financial losses for the local government, as Batu City’s revenue (PAD) primarily relies on agriculture and tourism, both of which depend on access through Trunojoyo Road. Geological methods provide valuable information about the distribution of rock formations locally. Geological mapping of the study area identified several rock units, including volcanic deposits, lava flows, Kawi-Buthak volcanic breccia, tuff deposits, and upper Quaternary volcanic breccia. Geophysical methods used in this study include gravity and magnetic surveys. The advanced method used is the minimum curvature inversion method. The gravity can detect faults using residual anomaly maps, with high values ranging from 0.1 to 3.0 mGal, moderate values from -0.8 to -0.09 mGal, and low values from -3.9 to -0.9 mGal. Meanwhile, the magnetic method provides insights into hydrothermal alteration by analyzing residual magnetic anomaly maps, ranging from -387.1 nT to 401.9 nT. Integrating geological and geophysical methods can establish a correlation between hydrothermal alteration zones and landslide activity. The correlation results between gravity, magnetic, and geological methods reached 99.4%, hydrothermal alteration zones and landslide activity had a correlation of up to 99.8%. The results indicate that both methods validate each other, yielding an accurate alteration map. Further correlation of this alteration map with landslide occurrences supports the hypothesis that hydrothermal alteration contributes to the landslides in the study area. Periodic reviews every year to obtain periodic data and references for government mitigation plans.