Executive Summary : | The post-collisional Himalayan belt has evolved as a thrust wedge in response to the continued convergence of the Indian and Eurasian plates. The progressive exhumation of crustal rocks led to the growth of the Higher Himalaya during the Miocene with the initiation of the summer monsoon. The tectonic-climate coupling produces rapid exhumation and massive erosion leading to the deposition of molassic sediments in the foreland basin during the mid-late Miocene. The Plio-Pleistocene global cooling saw a rapid mountain-building southward extension of the mid-upper crustal tectonic wedge in the frontal belt along the basal decollement (MHT) that produced large-scale landscape change and drainage reorganisations in the Himalayas. The active landscape evolution is primarily a function of competing processes of tectonic uplift and fluvial erosion. Thus, regional drainage reorganisation in tectonically active terrain leads to the regional base level change and large-scale drainage area exchange, impacting the evolution of topographic relief and drainage discharge in surrounding basins. The signature of past tectonics and climate histories often preserve in the topographic relief, longitudinal profiles, and abandoned channel landforms. Generally, a river profile tends to achieve dynamic equilibrium by matching the rock uplift rate with the incision rate and setting an uplift-erosion regime. Any perturbation (e.g., change in tectonics, climate, and eustatic) would lead to the initiation and headward propagation of a transient signal as an incision wave (slope-break knickpoint) from the local base level (e.g., Mountain front). Several such transient signals have been reported across the Himalayan arc and interpreted as a signal of active tectonics. These transient signals are crucial for understanding the spatial and temporal evolution of the Himalayan wedge. Modelling these transient signals would constrain the net surface uplift and differential erosion, with temporal constraints from provenance and thermochronology studies. The paleo elevated low relief landscape (ELRL), often indicates an abandoned in-situ developed surface due to either drainage capture or divide migration. This area exchange may lead to positive feedback between active tectonics and erosion and can be investigated for spatial and temporal variability of the transient signals across the wedge. The degree of surface uplift and perturbation timing can be constrained through paleo-base-level reconstruction and volume-for-time substitute and can be validated with the celerity test. Wind gaps involving the drainage area exchange can be identified through chi-analysis, which helps in understanding the dynamics of landscape evolution vis a vis tectonic variability. It is proposed to model major drainage systems, namely Lohit, Dibang, Siang-Yarlung, Subansiri, Kameng, Manas, Tista, Kosi, Ghagra, Gandak, Kali, Ganga, Jamuna, Satluj, Chenab, Jhelum and Indus River covering the Himalaya arc. |