Landslide erosion controlled by hillslope material

Steep hillslopes in mountain belts are eroded by landslides, and landsliding is ultimately driven by the topographic relief produced by fluvial and glacial erosion(1-5). Landslide erosion rates are derived from estimates of landslide volume and can help to appraise landscape responses to tectonic, climatic and anthropogenic forcing. However, the scaling relationships-power-law equations that are used to estimate the volume of the landslide from the area of the failure-are derived from a limited number of measurements, and do not discriminate between bedrock and soil landslides. Here we use a compilation of landslide geometry measurements from 4,231 individual landslides to assess the relative volume-area scaling of bedrock and soil landslides. We find that shallow, soil-based landslides can be approximated by an exponent of gamma = 1.1-1.3. In contrast, landslides that involve the failure of bedrock have a deeper scar area, and hence larger volume, and are characterized by gamma = 1.3-1.6. On the basis of observations that soil residence times in uplifting mountains can be as low as a few centuries(6), we suggest that both deep bedrock and frequent, shallow soil landslides can erode steep hillslopes at rates commensurate with even rapid tectonic uplift.