A GEOMORPHIC EVALUATION OF THE LANDSLIDES AROUND DEHRADUN AND MUSSOORIE, UTTAR-PRADESH, INDIA

The Mussoorie hills of northern India are characterized by a rugged to pography, 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 ove r the Neogene sedimentary rocks (Siwalik Group) along the Main Boundar y Thrust. Various geomorphological parameters have been assessed, in c onjunction with the geological and anthropogenic aspects, to evaluate the occurrence of the different types of landslides in the area. The e vidence of neotectonism was provided by the various geomorphic criteri a. Seventy-five landslides were identified by remote sensing. These we re studied in the context of geological aspects such as lithology, pro ximity to active faults and lineament density, geomorphological aspect s such as landform, slope, lateral erosion by streams, drainage textur e, spring sapping, elevation difference between adjacent valleys, alti tude and relief and anthropogenic factors including landuse/land cover and distances from roads. The important causes were found to be litho logy, 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 i nclude rainfall and seismicity. The preventive measures to be adopted to stabilise the slopes have also been described.