Late Quaternary (Holocene) landscape evolution of a monsoon-influenced high Himalayan valley, Gori Ganga, Nanda Devi, NE Garhwal

The Garhwal Himalaya provides an excellent natural laboratory in which to examine landscape evolution in a monsoon-influenced high mountain environment. Geomorphic and sedimentological analysis and 10Be cosmogenic radionuclide (CRN) surface exposure dating of moraines, fans, and river and strath terraces in the Gori Ganga Valley of Nanda Devi, NE Garhwal, indicate that fans and river terraces developed rapidly by debris flow and flood processes during periods of deglaciation. These phases of high sediment transfer occurred at ∼1–2, ∼4–5, and ∼7–8 ka. Fan incision rates, subsequent to major times of resedimentation after each glacial advance, are between ∼19 and 57 mm/year. This contrasts with bedrock incision rates, based on mid-Holocene strath terraces, of ∼5 mm/year. These rates indicate that despite episodes of rapid denudation and resedimentation linked to glacial activity in this region, the background rates of denudation are similar to those for other regions of the Himalaya, averaging several millimeters per year. Furthermore, these data show the importance of climatic controls on landscape evolution and suggest a strong monsoonal control on the dynamics of earth surface processes in this region.