A GIS-based Spatial Prediction of Landslide Hazard Zones and Mapping in an Eastern Himalayan Hilly Region Using Large Scale Soil Mapping and Analytical Hierarchy Process

Landslides are a serious threat to the sustainability of mountain ecosystems. In India, the Himalayan region suffered substantial economic loss and loss of life in the last couple of decades due to frequent landslides. However, identifying potential landslide hazard zones (LHZ) in eastern Himalayan regions helps to manage better and avoid economic losses. This study mapped LHZ of Mangan block, North Sikkim district, Sikkim state (India) in the eastern Himalayas, using GIS techniques. We carried out a landslide survey and characterized the soils at 1:10,000 scale, and used the analytical hierarchy process (AHP) method to map the LHZ using environmental (geology, land use/land cover, rainfall), terrain (elevation, slope, aspect, drainage density, lineament density), and soil (depth, texture, gravel content, erosion, land capability class) parameters. Relative rating values were assigned for the subclasses of each thematic layer based on their corresponding impact on the landslide triggers. Further, within a thematic layer, each class was assigned an ordinal rating from 1 to 9. The LHZ map of the Mangan block was produced based on weighted overly techniques. Higher weight was assigned for more influence, and lower weight was assigned for less influence of landslides. The results showed that high-intensity annual rainfall (similar to 3000 mm), elevation (1000-3000 m), coarse soil texture, strong to steep slope (30-60%), geology (inter-banded Chlorite-sericlie and banded Migmatile), and high drainage density are the main causal factors of landslides. The LHZ map shows that the landslide hazard is moderate at 47%, high at 46%, and very high in 4.5% of the study area. Landslide hazard is high in areas with soils of Ringhim (RGM), Nampatam (NPM), Kazor (KZR), Singhik (SGK), and Siyam (SYM) series than in other soils. The LHZ map was validated using the field observations, and most of the recorded landslides (rockfall, debris flow, slope failure induced soil mass toppling, and earth flow) occurred in the moderate to high LHZs on the map. The LHZ map can be used for landslide hazard prevention, infrastructure development planning, and geo-environmental development in the Mangan block.