RATES OF LANDSCAPE EROSION IN ZANSKAR, NORTHERN INDIA

Determining geomorphic rates of erosion has traditionally been challenging due to inherent difficulties associated with making physical measurements and instrumentation. This is especially true in mountainous environments where high magnitude events such as floods, debris flows and landslides may damage equipment and skew results. In recent years, however, erosion rate studies have been aided by continuing developments in terrestrial cosmogenic nuclide (TCN) methods. Using ¹⁰Be TCNs, two large (>300 km²) valleys in the arid, high-altitude Zanskar Range of the northwest Indian Himalaya are studied to determine the spatial variation of erosion to examine what factors influence erosion rates. Both valleys are half-grabens and were glaciated to different extents. Sub-basins within these valleys can be categorized by primary erosive influences based on their geologic history: 1) tectonic-dominated; 2) glacial-dominated; 3) tectonic and glacial influenced; and 4) sub-basins with no evidence of tectonic and glacial influence. Spatially-averaged basin wide erosion rates were determined for 19 sub-basins and the main valleys to establish regional norms and to examine the effect of contributing factors (e.g. relative uplift and relief production, glaciation). In addition, erosion rates were determined on bedrock at valley ridges to determine any spatial controls on bedrock erosion rate. Preliminary results show that erosion rates for this region are generally low (< 10 m/Ma basin-wide erosion; < 5 m/Ma bedrock erosion) with the highest rates of erosion (~ 130 m/Ma) occurring in small basins in the footwalls of the half-grabens. These results suggest that relief production due to relative uplift may be the dominant contributor to erosive processes in the region.