Landslide hazard zones differentiated according to thematic weighting: Road alignment in North Sikkim Himalayas, India

Geospatial analysis is a powerful tool for assessing landslide frequency distribution and hazard potential zones along road alignment in North Sikkim Himalayas, India. The thematic weightings used for road alignment include slope angle, slope aspect, lithology or rock types, hydrological characteristics (drainage lines), fault and thrust present, road alignment, and surface cover type. Each parameter can be assigned a numerical value based on its potential contribution towards increasing landslide susceptibility; higher values indicate greater risks while lower ones suggest less danger from these events occurring along that stretch of roadway or landform feature. Thematic weighted method has determined the weight values of various preparatory factors based on their vulnerability and estimated the landslide hazard index (LHI) by classifying the study area into four distinct hazard zones: very high (12.12%), high (40%), moderate (37.20%) and low-hazard zone (10.68%). The result reveals that 65.3% of landslides occurred in the very high-hazard zone. About 24.7% and 7.6% of the landslides were found in high and moderate-hazard zones. Only 2.4% of landslides contribute to a low-hazard zone. It has been found that the landslide frequency percentage gradually increases from low (2.4%) to very high hazard zone (65.3%). This mapping also helps planners decide where construction activities should not be performed if they are located within these hazardous zones thus helping reduce future losses due to such calamities are significant.