Quaternary deformation, river steepening, and heavy precipitation at the front of the Higher Himalayan ranges

New geologic mapping in the Marsyandi Valley of central Nepal reveals the existence of tectonically significant Quaternary thrust faults at the topographic front of the Higher Himalaya. The zone of recent faulting is coincident with an abrupt change in the gradient of the Marsyandi River and its tributaries, which is thought to mark the transition from a region of rapid uplift in the Higher Himalayan ranges to a region of slower uplift to the south. Uplift of the Higher Himalaya during the Quaternary is not entirely due to passive uplift over a deeply buried ramp in the Himalayan sole thrust, as is commonly believed, but partially reflects active thrusting at the topographic front. The zone of active thrusting is also coincident with a zone of intense monsoon precipitation, suggesting a positive feedback relationship between focused erosion and deformation at the front of the Higher Himalayan ranges.