Tectonic, lithologic and climate controls on landslide distribution in the Eastern Himalayas

Regions dominated by active fold and thrust belts are prone to the development of new, unstable slopes as deformation progresses. However, studies examining the spatial distribution and behavior of landslides within the Himalayas—one of the world’s most dynamic mountain systems—remain limited. This study presents a detailed landslide inventory for the Sikkim Himalayas, an area marked by vigorous tectonic activity and steep, rugged landscapes. By analyzing satellite imagery, we compiled over 100 large-scale landslides (each exceeding an area of 10⁶ m²), with many of these still exhibiting active movement. We utilized tools such as TopoToolbox to analyze topographic steepness and concavity indices, as well as factors like proximity to rivers and active faults. Additionally, geomorphic indices of active tectonics, lithological variations, and rainfall patterns were integrated to investigate the relationship between landslide distribution and these variables within sub-basins as well as across major thrust zones. In Sikkim, landslides show a pronounced tendency to cluster at higher elevations, specifically in the zone between the Main Central Thrust (MCT) and the South Tibetan Detachment (STD). These events are predominantly concentrated in areas with significant local relief and are closely linked to regions experiencing higher rates of relative tectonic uplift. Moreover, extreme rainfall driven by orographic effects amplifies landslide activity, particularly in regions with steep terrain. The most affected areas include the uppermost, steepest areas of active thrusts (MCT and Main Boundary Thrust) and inclined escarps of deeply incised valleys.