Association of landslides with geological structures and rainfall: a case study of two landslides in Sunkuda, Nepal

Nepal is home to numerous large landslides. These landslides emanate from both intrinsic and extrinsic factors. Though, prevalent in Himalaya, landslides resulting from underlying geological features are given lesser attention. The present research investigates the evolution and progression of two landslides from Sunkuda region, Western Nepal—and their association with the underlying geological structure. Two landslides, A, and B, from the study area present continuous downslope movement. In order to understand the causal factor, geological, geomorphological, and geophysical survey was conducted in the landslide affected area. Geotechnical attributes were obtained to understand the behaviour of the groundmass. Investigation led to the discovery of a thick band of shear zone nearly 35–40 m on the upper slope and 10–20 m on the lower slope, affecting the stability of the hill slope. Both landslides occur within the crushed zone of the thrust. The research found that the pore water transmitted through the developed shear zone increases the pore pressure and triggers failure. Intense monsoonal rainfall was observed and taken into consideration. Furthermore, the evidence indicates a major role played by the thrust fault behind the genesis and evolution of both landslides. It is also found that anthropogenic activities, gully erosion, and toe-cutting by the stream also had a crucial role in the evolution of landslides.