Morphotectonic Evolution of the Siwalik Hills between the Yamuna and the Markanda River Exits, NW Himalaya

ABSTRACT The Main Frontal Thrust (MFT) marks the present day active deformation front of the Himalaya and separates it from the Indo- Gangetic plains. The dynamic growth of the outermost Siwalik hills due to thrusting along the MFT has a direct influence on the drainages which collectively control the landform evolution of the region. In this study, the Siwalik hills (called as the Dhanaura range in the study area) between the Markanda and the Yamuna river exits in the NW Himalaya is investigated for its morphotectonic evolution using geomorphic indices, longitudinal river profiles, and topographic profiles. The results suggest presence of at least four structures that have merged to form the Dhanaura range. The first expression of the Siwalik hills was marked by the uplift of the surface due to a blind thrust in the northwestern part of the study area, followed by the growth of the Pataliyon anticline along a northeastern segment. The growth of the Dhanaura anticline occurred later by the merging of three MFT segments in the southern part of the study area. The Dhanaura anticline formed a barrier to the drainages arising from the initial northern topography, forcing them to get deflected. There also exists an unidentified structure to the north of the Dhanaura anticline as evident from the longitudinal river profiles, structural data, and drainage network of the area. Low mountain front sinuosity ratio, moderate hypsometric integral (HI) values and tilting of drainage basins in the study area suggest the structures are active.