Topographic stress control on bedrock landslide size

Abstract

Landslides are a major natural hazard and act as a primary driver of erosion, chemical weathering and organic carbon transfer in mountain ranges. Evaluating the impact of landslides on Earth systems requires knowledge about the controls on their size, which are not well understood. Here we show that topographic stress, resulting from the interaction between tectonic stress and topography, influences bedrock landslide size at landscape scales by modulating the subsurface material strength through fracturing and weathering. Using a three-dimensional topographic stress model, we characterize the spatial pattern of subsurface open-fracture zones in a crystalline-rock terrain of the eastern Tibetan mountains. Then, we compare the predicted open-fracture zones with 982 mapped bedrock landslides. The results show that areas with deeper subsurface open-fracture zones tend to accommodate larger landslides. This is probably due to the influences of topographically induced fractures on the material strength and groundwater flow paths and rates. We conclude that the extent of hillslope failure depends on both distant tectonic forces and local topography, which has implications for hazard mitigation, landscape evolution and the global carbon cycle. Stress from tectonics and topography may be the primary control on the size of bedrock landslides, according to a comparison of a stress model with landslide inventories for a mountainous area in eastern Tibet.