CLIMATIC AND TECTONIC INFLUENCES ON CATCHMENT-MEAN DENUDATION RATES IN THE ARUN VALLEY, EASTERN NEPAL
In order to quantify denudation variability in the Arun with respect to climate, vegetation, and tectonics, we collected 48 river sand samples for catchment-mean CRN analysis. Samples were collected from the main stem of the Arun and its tributary watersheds. Denudation rates across the Arun valley range from 0.33 ± 0.03 mm yr-1 (n=10) in the Lesser Himalaya to 0.77 ± 0.07 mm yr-1 (n=14) in the Higher Himalaya. Catchment-mean denudation rates do not strongly correlate with standard uplift-related topographic metrics (e.g., slope, channel steepness, relief), and negligible relation to lithology or mean annual rainfall. Instead, denudation is best described by TRMM-weighted specific stream power (SSP), while vegetation density appears to buffer erosion in landslide-dominated catchments. We argue that, in contrast to recent studies in the central and western Himalaya, centennial to millennial denudation in the Arun Valley is not only dominated by tectonics. While tectonic uplift sets the large-scale spatial pattern of denudation, we conclude that the interplay of multiple factors and not a single tectonic or climatic signal drive denudation.