Geomorphic evaluation of landslides along the Teesta river valley, Sikkim Himalaya, India

Landslides are a common and widespread phenomena in tectonically active mountains, impacting on landscape development, and lanslides pose a serious threat to the lives and properties when these interfere with humans and their associated infrastructure. However, the spatial distribution of these landslides is controlled by various geological and geomorphological parameters, including the neotectonic activity and the climatic pattern of the area. In the present study, various geomorphic parameters such as longitudinal and topographic swath profile, valley floor width to valley height ratio, channel steepness index, and stream length gradient index, along with the rainfall pattern of the Teesta river valley, Sikkim Himalaya, were correlated with the spatial distribution of landslides in the area. It has been concluded that landslides in the Higher Himalaya, north of the Main Central Thrust behind the orographic barrier, owe their origin mainly to the higher tectonic activity, and adjacent to the Main Central Thrust in the front of the orographic barrier to both tectonic activity and the higher rainfall. The distribution of landslides in the Lesser Himalaya is dominantly controlled by lithology and is mainly triggered by the rainfall. Landslides and associated mass movement phenomena in the Sikkim Higher Himalaya owe their origin mainly to the higher tectonic activity behind the orographic barrier and to the tectonic activity and rainfall in front of the orographic barrier, particularly between Mangan and Rangrang, whereas the landslides in the Lesser Himalaya are dominantly controlled primarily by the rainfall.