Geomorphic mapping and investigation of the uplifted piedmont zone between Haridwar and Kotdwar, Indo-Gangetic Plain, India

Abstract

Active tectonics plays a crucial role in the landscape evolution at the decadal to thousand to million-year time scale. Datasets to examine landscape changes at a decadal scale are rare in the Indo-Gangetic Plain (IGP), which is one of the most dynamic areas in the Himalayan orogenic front. In this paper, we report decadal-scale landscape changes, which occurred in the last 40 years in the piedmont zone of the Haridwar – Kotdwar region due to an active blind fault in the IGP. The identification of tectono-morphic features in IGP is difficult to comprehend due to the combined effect of climatically induced sediment supply and tectonically driven subsurface deformation of alluvium sediments in the piedmont zone. We used various satellite imageries and aerial photographs available from 1970, to detect and map the changes in the flow pattern of rivers in the study area, which resulted due to gradient change. Using optical satellite imagery, geomorphic indices, and field investigation, we mapped various morpho-tectonic features in the piedmont zone. Due to uplift caused by upwarping, a topographic high of ~40 ​m is observed in the Malin Fan, which has led to the migration of the subparallel rivers emerging from the Sub-Himalaya. We report an eastward shift of ~8 ​km in a period of ~40 years by the Malin River; the Khoh River also migrated towards the east and the Sigadi Sot River migrated towards the west abandoning its paleo courses. We propose that the neotectonic deformation by the subsurface Najibabad Fault (NF) has caused an upwarp of the Malin alluvial fan in the western Ganga Plain. The Gradient Length Index (GLA) anomalies calculated for the major rivers in the study area also show a series of negative anomalies, which is in agreement with an upliftment zone in the IGP. Remote sensing and morphometric analysis identified the potential uplift zone ~5 ​km north of NF in the piedmont zone, which is supported by field studies. It is concluded that the slip along NF will be essential to understand the evolution of the piedmont zone, which is actively deforming and can be a potential seismic hazard zone in the future.