Tectonic and geomorphic drivers control the evolution of landforms in the Eastern Sub-Himalayan and Piedmont zone

The mountain to the foothill plain of the Himalayas has diversified topographic signatures. The present study identified the imprints of tectonic and fluvial stressors in the Sub-Himalaya, Piedmont, and foothill regions of the eastern Himalayas. Satellite images, SRTM, and ALOS PALSAR DEM data were used to demarcate different geomorphic features. The geomorphic indices like the Mountain Front Sinuosity (S_mf) Index, Gradient Length Anomalies (GLA), and Valley width to height (VF) ratio were used for the analysis of active tectonics. The geomorphological attributes of three gully fan segments were identified for the analysis of fluvial stressors. The result shows that the S_mf value varied between 1.38 and 2.40, and the highest value indicates the inactive mountain front (MFS-8) near Samtse of Bhutan. The negative anomaly is 0.064–0.00035 while the positive GLA ranges between 0.032 and 0.064. There are two positive anomalies recorded within the Jaldhaka and Ghatia rivers. The VF value of 1.63 of the Kuchi-Diana River is the highest, indicating the incision of the valley floor. The geomorphological attributes of the gully fan were identified as the retreat of the gully fan, which refers to the impact of high slope gradient and fluvial action in the scarp of the fan surfaces.