A geomorphic evaluation of the landslides around Dehradun and Mussoorie, Uttar Pradesh, India

The Mussoorie hills of northern India are characterized by a rugged topography, with hill ranges rising steeply from about 600 m above mean sea level to over 2300 m and deep cut valleys. The area comprises the Proterozoic-Cambrian rocks of the Krol belt which have been thrust over the Neogene sedimentary rocks (Siwalik Group) along the Main Boundary Thrust. Various geomorphological parameters have been assessed, in conjunction with the geological and anthropogenic aspects, to evaluate the occurrence of the different types of landslides in the area. The evidence of neotectonism was provided by the various geomorphic criteria. Seventy-five landslides were identified by remote sensing. These were studied in the context of geological aspects such as lithology, proximity to active faults and lineament density, geomorphological aspects such as landform, slope, lateral erosion by streams, drainage texture, spring sapping, elevation difference between adjacent valleys, altitude and relief and anthropogenic factors including landuse/land cover and distances from roads. The important causes were found to be lithology, proximity to the active faults (Main Boundary Thrust and Sairku fault), slope angle and aspect, lateral erosion by stream undercutting and deforestation due to human interference. The triggering factors include rainfall and seismicity. The preventive measures to be adopted to stabilise the slopes have also been described.