Style and timing of glacial and paraglacial sedimentation in a monsoon-influenced high Himalayan environment, the upper Bhagirathi Valley, Garhwal Himalaya

Abstract

The Gangotri Glacier, at the source of the Ganges River, has fluctuated greatly throughout the late Quaternary in response to climatic oscillations. This has resulted in impressive moraines, paraglacial debris flow fans and terraces along the upper stretches of the Bhagirathi Valley. Cosmogenic radionuclide (CRN) dating of glacial and paraglacial landforms shows that fans, terraces and associated moraines formed approximately synchronously as the landscape readjusted to changing environmental conditions. This synchronicity suggests that fan and terrace formation is intimately related to glaciation, and that fluctuations in glacial and associated environments during times of climatic instability cause rapid sediment transfer and resedimentation of glacial landforms. The CRN dates show that all existing glacial and paraglacial landforms in the upper Bhagirathi Valley formed during the late Pleistocene and Holocene. This demonstrates that, in this high mountain environment, paraglacial and glacial landforms are eroded and resedimented within about 20,000 years. Furthermore, this testifies to the dynamic nature of glacial environments in monsoon-influenced high mountain regions.