Analysis of hillslope erosion rates using dated colluvial deposits

Hollows are sites of long-term deposition of colluvium and contain a valuable record of the timing and rates of hillslope erosion. A model is presented that uses measured depositional rates of colluvium in hollows to calculate transport rates of colluvium and bedrock lowering rates on the surrounding slopes. This model has been applied to eight dated colluvial deposits in the Clearwater River basin of western Washington. The calculated average transport rate is about 34cm³/cm/yr, and the calculated average bedrock lowering rate is about 40B, equivalent to an average sediment yield of 90t/km²/yr for the Holocene. Most basal dates from the hollows are early Holocene in age, a time of warmer and drier climate, suggesting a period of widespread evacuation of colluvium and increased sediment yield. -from Authors