Morphometric analysis of tectonically active Pindar and Saryu River basins: Central Kumaun Himalaya

摘要

Morphometric analysis in association with fluvial landform study has been used to ascertain the tectonic instability/stability in Pindar and Saryu River valleys of the central Kumaun Himalaya. To assess tectonic activities in the area, geomorphic indices namely, stream-gradient index (SL), drainage basin asymmetry (AF), topographic asymmetric factor (T), Valley-Floor Height Ratio (Vf) and Elongation Ratio (Re) have been studied. The results of morphometric analysis are in consistent with the field evidences. The study suggests that the terrain close to Main Central Thrust (MCT) and the North Almora Thrust (NAT) is undergoing deformation, which is attributed to the regional compression. More specifically, using the valley morphology and longitudinal river profile, the Pindar and Saryu River valleys are divided into three and two broad tectonomorphic zones, respectively. In the Pindar River valley, zone-1 is bounded by the MCT1 to MCT3, Dwali-Phurkiya Fault (DPF), Dulam-Khati Fault (DKF), zone-2 by Askot Thrust (AT) and Baijnath Thrust (BjT) whereas zone-3 is demarcated by Narayanbagar Thrust (NT) and Alaknanda Fault (AF). The two zones in Saryu River valley are bounded by MCT 2 to 3, DKF and AT, NAT. The study suggests that the above-mentioned structures exert significant influence in the evolution of fluvial landform, thus advocates tectonically active nature of the terrain. These structures are considered to be tectonically active. Integrating the morphometry and the geomorphic expressions of tectonic instability suggests that in Pindar River zone-1 and zone-3 are more tectonically active compared to zone-3, whereas in Saryu River valley, zone-2 shows enhanced deformation.