Evaluating the influence of anthropogenic hillslope modulation in relation to shallow landslides in the Rishikhola region, Darjeeling–Sikkim Himalaya, India

Shallow landslides are pervasive geomorphic threat in mountain terrain, especially where intense precipitation, steep relief, and land-use changes overlap. This research investigates the geotechnical and hydrological behavior of hillslope materials under three types of land uses cultivated (terraced), dispersedly vegetated, and dense forest areas in the landslide-prone area of Rishikhola in the Darjeeling-Sikkim Himalaya. Soil samples were tested for grain size distribution, bulk density, porosity, moisture content, pH and compaction properties. Results indicate that cultivated areas show greater compaction (bulk density up to 1.62 g/cm³), reduced porosity (~ 39.6%), higher moisture content (> 32%), and more acidic pH (5.3-5.5) and these conditions collectively diminish soil strength and increase pore-water pressure, thereby predisposing the slopes to heightened instability under intense or prolonged rainfall.. Dense forest areas, on the other hand, exhibited comparatively lower compaction, balanced moisture regimes, and near-neutral pH values (5.95-6.28). These conditions contribute to enhanced slope stability through improved infiltration, microbial processes, and root reinforcement in the dense forrest areas. The results highlight a distinct gradient of landslide susceptibility according to land use patterns. This research also presents transferable knowledge for other active tectonic and monsoonal-influenced mountain belts worldwide, where the interaction between land use, soil properties and slope hydrology plays a critical role in shallow landslide susceptibility. The findings reaffirm the need to incorporate ecological restoration into mitigation strategies in the Himalayan and similar high-relief environments globally.