Catchment‐wide denudation rates at the margin of NE Tibet from in situ‐produced cosmogenic 10Be

Terra Nova, 23, 42–48, 2011 Abstract We present denudation rates for catchments in the Qilian Shan and two mountain ranges in its foreland, which differ markedly in elevation and catchment morphology. Catchments with mean slope angles below ∼25° yield 10Be-derived denudation rates <∼200 mm ka−1 and have narrow and symmetric slope–frequency distributions, which become broader as the mean slope angle increases. Denudation rates for catchments with mean hillslope angles steeper than ∼25° range from ∼100 to ∼800 mm ka−1. Field observations suggest that these higher and more variable rates are the result of erosion by bedrock landslides, which contribute to mass transport on the hillslopes. Six catchments aligned along the mountain front of the central Qilian Shan have reached threshold values of slope and relief. These basins also show remarkably similar slope–frequency distributions with negative skewness and a pronounced peak at a slope angle of 30°–35°. We hypothesize that these catchments have attained an erosional steady state.