Himalayan Geology, Vol. 43 (1B), 2022, pp. 371-382, Printed in India
Morphometric Characterization and Tectonic Geomorphology of the Upper Beas basin, Himachal Himalaya, India
SARABJEET SINGH1, TEJPAL SINGH2*, SEEMA SINGH1, A.K. AWASTHI3
1Department of Geology, Panjab University, Chandigarh - 160014, India
2CSIR-Central Scientific Instruments Organisation, Chandigarh - 160030, India
3Formerly at the Department of Earth Sciences, IIT-Roorkee, Roorkee - 247667, India
*Email (Corresponding author): tejpal@csio.res.in
Abstract: The Upper Beas basin from its origin in the Beas Kund (at elevations in excess of 4500 m above msl) till Mandi town in the downstream (at ~750 m above msl) makes a steep descent of around 4 km in ~125 km. This part of the basin is characterized by glacial-fed rivers and tributaries that form a perennial drainage system. In general, from its headwaters in the north of Manali the river flows from north to south till Aut/Larji where it takes an abrupt rectangular turn and flows towards the west. Further downstream it takes another rectangular bend at Pandoh to flow in a northerly direction. The Beas River again takes an abrupt right-angle bend to flow in a southwest direction upto Mandi town. The river in this part of the basin is highly asymmetric where the left divide is almost 60 km away from the main channel whereas the right divide is only 10-20 km away. These conspicuous changes in river behaviour and pronounced anomalies in basin geometry motivate the present investigation that look into: 1) the morphometric characterization of Upper Beas valley, 2) identify spatial zones based on morphometry and 3) draw inferences on the evolution of the morphometric zones with emphasis on the tectonics and geomorphology of the Upper Beas basin. Based on this investigation, we are able to identify three distinct morphotectonic zones in the Upper Beas basin and suggest the dominant surface processes shaping the basin geometry in case of each of the three zones. The zone 1 has predominantly evolved by capture and lateral coalescence. The basin evolution is controlled by the limiting topography of threshold hillslopes towards north. The zone 2 has predominantly evolved by headward elongation and capture. The basin evolution is controlled by the Rapid Exhumation Zone (REZ) in this part. The zone 3 has predominantly evolved by mouthward elongation and capture of drainage truncated by a frontal ridge. This zone also demonstrates genetic linkages between the ridge topography and basin geometry. The close correspondence of these linkages with the MBT indicates to a strong control exerted by the MBT on the evolution of zone 3.
Keywords: Morphometric Characterization, Tectonic Geomorphology, Beas basin, Himachal Himalaya
