Denudation and landslides in coastal mountain watersheds : 10,000 years of erosion

Abstract. A conceptual model of landslide-induced denudation for coastal mountain watersheds spanning 10,000 years of environmental change is presented. The model uses a constructed paleo-climate based on vegetation records and an established relationship between landslide frequencies and precipitation. Landslide frequencies are determined for the early warm dry Holocene, the warm wet middle Holocene and modern climates. Average landslide rates vary between 0.005 landslides·y^-1·km^-2 and 0.008 landslides·y^-1·km^-2. Recent human impacts are calculated by recalculating landslide frequencies for logged areas in the 20^th century. The impact of logging during the last 100 years is unambiguous as landslide frequency increased to 0.015 landslides·y^-1·km^-2. This suggests that the impact of logging outpaces that of climatic change. It is estimated that debris slides and flows eroded an average of 0.7 m·m^-2 across Vancouver Island during the last 10,000 years.