Neotectonically triggered instability around the palaeolake regime in Central Kumaun Himalaya, India

Abstract

Mass wasting often results from the combined effect of tectonic and climate processes. It has not only resulted in human casualties on large scale but has also ruined agricultural land and disrupted hydro power projects and other governmental as well as private property. Despite the belief that prevention is inevitably better than cure, decrease in future hazards requires proper dissemination of knowledge to the Himalayan inhabitants. Considering this, we investigated a part of Kumaun Himalaya to understand the cause of cloud burst induced mass movements along the Saryu River that took place on 18th August 2010 and subsequently on 12–14th September, 2012. A number of Quaternary faults, e.g., Dulam fault (DF), Dulam Gadhera Fault (DGF) and Vongarh-Gason Fault (VGF) in the zone of a major thrust (Berinag Thrust) in the studied sector are invariably active as evident by various geomorphic features, e.g., saw cutting of host rocks, immature topography, deflecting river courses, ponding of ancient drainage, development of cascades, formation of unpaired fluvial terraces, and series of triangular fault facets. The fragile lithology, deep V shaped valleys, accelerating erosion and incision with higher uplift due to tectonic upheaval along the active faults are also responsible for rainfall induced catastrophes in the region. Additionally, morphometric analysis reveals that the Saryu basin is elongated and tilted. Further, the tectonic tilting and moderate to coarse drainage density may possibly be responsible for quicker runoff, amplified erosion, and subsequently increased flooding around the study area. We infer that the area is not only controlled by topography but may also have been affected by the hydraulic factors such as climate. In addition, the drainage is dominated mostly by first order streams which seem to be indicative of higher chances of flooding, as most of the water is concentrated in a single channel during monsoon season. We believe that the similar studies done in the other sectors will be helpful in reducing not only the huge loss of life but may also help in protecting ongoing and huge hydropower and other developmental projects in this newly born state.