Neotectonic Landform Development and Associated Mass Movements along Eastern Ramganga Valley in the Kumaun Himalaya, India

The present study focuses on the neotectonics activity and related mass movement along the Eastern Ramganga River Basin (ERRB), Kumaun Himalaya, India. To understand the contemporaneous landform development, the quantitative analysis of drainage network is combined with field-based geomorphic attributes and recent seismicity data. The Ramganga River traverses across major thrusts, e.g., Main Central Thrust (MCT), Munsiari Thrust (MT) and Berinag Thrust (BT), and subsidiary faults, e.g., Namik Fault, Kaphli Fault, Hokara Fault, Kaphlikot-Ramari Fault and Ramganga Fault. Furthermore, the NNW–SSE trending faults (e.g., Naulara-Chilkiya Fault (NCF) and Nankana-Kapisar Fault (NKF) were also demarcated by means of characteristic geomorphic features in the upper catchment of the basin. The observed geomorphic elements such as uplifted fluvial terraces, several small to large waterfalls, fault facets, active and stabilized landslides, deflected and migrated streams, wide/straight river course converting into narrow passage, entrenched river channels, palaeo-channels and dissected hills etc. demonstrate symptomatic footprints of landscape evolution within the basin and also reveal that the thrusts/faults traversing through the ERRB are reasonably active. The field investigations are further verified by measuring various morphometric indices, results of which indicate elongated and asymmetric valleys, highly dissected drainage basin, high relief, sharp deflections in streams, slope breaks with remarkable values of stream length gradient index (SL) and steepness index (Ks). Further, we observed anomalous geomorphic expressions with possible surface deformation within thrust/fault zones as well as along anticlinal axis in the upper catchment which is characterized by higher slope, relief, accelerated erosion, incision, uplift and mass movements. Such features in the thrust/fault-fold belt of the region and recurrent seismicity appear responsible for triggering severe landslides under intense rainfall. The outsized disastrous landslides have resulted in destruction of human settlement, disconnecting road networks, damage of property and loss of lives particularly during the monsoon period. Therefore, we recommend that proper geological and geo-technical surveys are of utmost importance to identify susceptible sites all along the basin length.