Himalayan Geology, Vol. 43 (1A), 2022, pp. 73-84, Printed in India

A study on the causative and triggering factors of multiple landslides in Lalmati, Nagaland and development of a sinking zone

WEYEPE N. MEKRISHU*, SOMENDRA K. SINGH, P.S. NINGTHOUJAM, GONMEI Z. PIUTHAIMEI

Department of Geology, University of Delhi, New Delhi-110007, India

*Email (Correspondence author): weyepemekrishu@gmail.com

Abstract: Landslides are inevitable and quite common natural phenomena in tectonically active mountain chain where they annually recur during monsoonal events. The study area lies in the tectonically unstable Inner Fold Belt of Indo-Myannmar Range (IMR) and is lithologically characterised by weak Disang and Barail groups of rocks. Asian Highway-1 passes through this landslide-prone area where sliding occurs regularly over the years during the monsoon. The scientific study of landslide assumes importance in the backdrop of the nature of its vulnerability and economic implication for the states of Nagaland and Manipur, and to propose a remedial measure to mitigate the hazards. Toward this, analytical assessment of the geological attributes is undertaken to find a quantitative linkage with the landslide. Based on the field studies and application of Remote Sensing (RS) data, we suggest that the major causative factors of landslide are: the fragile nature of the lithology, thick colluvial overburden deposits, toe erosion and anthropogenic activities while the main triggering factor is the torrential monsoon rain. Landslides occur when bedrocks and overlying colluviums become saturated with water after the torrential rain. The development of sinking zone as a result of gravity faults in the hanging-wall of the Disang Thrust that lies in hinterland have made this section of the study vulnerable to landslides. Re-evaluation of road alignment, proper drainage system and grouting are recommended remedial measures.

Keywords: Lalmati landslide area, Landslides, Monsoonal rain, Sinking Zone, Toe erosion, Remedial Measures