Spatial distribution of bedrock landslides over the landscape evolution in NW Himalayan River catchments

Abstract. The tectonically active North Western (NW) Himalaya landscape has evolved out of long-term active gradational interaction of major drainage systems. Landslides act as a primary erosion agent in these landscapes. We analyzed the spatial distribution of landslide occurrences along the Chenab, Beas, Sutlej, Yamuna, Ganga, and Kali rivers catchments in NW Himalaya to characterize landscape attributes. Further, spatial variability across different climatic zones viz., Western Disturbances –Indian Summer Monsoon (WD-ISM) was assessed. Seismicity and geochronological data were used to analyze the impact of bedrock landslides on landscape evolution. The denudation rate of the studied catchments was spatially correlated with exhumation age, precipitation intensity, and topographic variables. The highest probability of frequent landslides occurrence was found in the zones with ~24–32° of slope range, ~800–1200 m of relief range, in 1200–2400 m elevation range, which coincides with the precipitation erosivity range of ~1500–3000 mm/year in NW Himalayan river catchments. These zones also correlate well with the zones of cloudburst occurrences in NW Himalaya. Landslides in the Higher Himalaya, north of the MCT and across westerly dominated catchments such as Chenab, Beas, and Sutlej along the orographic barrier, are primarily triggered by higher tectonic activity. In contrast, landslides adjacent to the MCT in the front of the orographic barrier and across summer monsoon-dominated catchments such as Yamuna, Ganga, and Kali are controlled by litho-tectonics and mainly induced by higher precipitation intensity. It has been observed that catchments dominated by westerlies have a higher mean denudation rate and mean exhumation age than catchments driven by the Indian summer monsoon.