Transient Fluvial Response and Topographic Disequilibrium in the Rivers of the Darjeeling Sikkim Himalaya, India: Geospatial Inference on Tectonic Geomorphology

ABSTRACT The assessment of regional tectonic deformation on the earth’s surface, tectonically active landscapes, and the geomorphic manifestation of active tectonics through the use of sophisticated geospatial tools, short-term geodetic data, and longer-term geologic data is made possible here by tectonic geomorphology. The central-southern region of the Darjeeling Sikkim Himalaya (DSH), which is known for its transient fluvial landforms and active tectonics, is primarily characterized by the Lesser Himalaya and Quaternary piedmont fans. The complex river systems of the Tista and Jaldhaka drain it, and few earth scientists predict that significant earthquakes will probably strike this area soon. The current analysis of tectonic geomorphology indicates that the upstream migration of knickpoints, the shifting river gradient, and the anomaly in the channel steepness index are all caused by the continuous tectonic disturbance of the DSH, which accelerates fluvial incision in an upstream direction to maintain equilibrium. The goal of the current geospatial research work is to determine whether it is possible to predict seismic hazard zones or tectonic stress zones in the DSH by using the geomorphic parameters of the transient fluvial response, which is the morphology of a river profile that changes to fit shifting boundary conditions, such as tectonic upliftment, and thus creates a transient river basin. Because bedrock river networks tend to progressively carve mountain slopes and maintain signs of prior landscape changes, a study of these networks is essential to understanding the topographic evolution of the DSH orogens. The stream power incision model, normalised steepness index (Ksn), stream-length gradient index (SL), hypsometric integral (Hi), chi plot (χ), and knickpoint finder are MATLAB-based Topo Toolbox 2 functions for tectonic geomorphology that are used in the study of active tectonics. According to the primary finding, rivers with high Ksn values (between 100 and 305 m0.9), SL index (522-12098 gradient m) and Hi (>0.55) are associated with the major thrust effect zones. These zones are identified on river longitudinal profiles as probable locations of major tectonic stress. Rivers across the MFT (Main Frontal Thrust), MBT (Main Boundary Thrust), and MCT (Main Central Thrust) show notable departures from equilibrium (dominance of convexity over concavity) in river longitudinal profiles. This suggests that the uplift rate predominates over the fluvial incision rate, leading to the creation of gorges and linear valleys.