PALEO-LANDSLIDE REACTIVATION AND THREAT TO THE PEOPLE IN THE NEPALESE HIMALAYAS

A landslide is a devastating disaster commonly occurring in the Himalayas during the Monsoon period. Many people lose their life and property due to landslides in the settlement area. The Himalayas is fragile, weak, and morphologically dynamic due to the continuous collision of Indian and Eurasian plates. Several faults, thrusts, and highly jointed Himalayan rocks are causing the landslide activation and reactivation. Most of the Himalayas' settlements live on the Paleo-landslide deposits. This study focuses on the threat to people living in the Paleo-landslide deposits that are currently reactivating.

Paleo-landslides and people settlements near it were identified from satellite images and several field visits. Geological mapping, soil investigation, shear zone identification, and slip surface identification were conducted in the field. Some of the soil investigations, like texture, shear strength parameters, and Atterberg limit test, are performed from the Palep-landslides near the settlement to identify the leading cause of reactivation. A community survey is conducted to take public consent regarding the vulnerable situation due to landslides. A generalized linear model and multiple regression were performed for data analysis. The result shows that reactivated landslides threaten 52% of the Mountain settlements. Among the Paleo-landslide, 42% of landslides are reactivated, whereas 37% are ready for reactivation. The shear strength of reactivated landslides is significantly less than the non-reactivated landslide. The Paleo-landslide deposits are moving mostly than the old scar. Thrust, normal fault, shear strength of soil, permeable gravel deposit and high plasticity of soil are the leading causes of landslide reactivation. Identifying the old landslide and possible reactivation can help save the lives of Himalayan people facing the higher threat of landslides.