Landsliding and the evolution of normal-fault-bounded mountains

Much of the tectonic and climatic history in high-relief regions, such as the mountains of the western U.S. Basin and Range province, is contained in the morphology of hillslopes, drainage networks, and other landforms that range in scale from 10(-1) to 10(1) km. To understand how these landforms evolve, we have developed a numerical landscape evolution model that combines a detailed tectonic displacement field with a set of physically based geomorphic rules. Bedrock landsliding, long recognized as a significant geomorphic process in mountainous topography, is for the first time explicitly included in the rule set. In a series of numerical experiments, we generate synthetic landscapes that closely resemble mountainous topography observed in the Basin and Range. The production of realistic landscapes depends critically on the presence of bedrock landslides, and landsliding yields rates of long-term erosion that are comparable in magnitude to those of fluvial erosion. The erosive efficiency of bedrock landsliding implies that hillslopes may respond very quickly to changes in local base lever and that fluvial erosion is the rate-limiting process in steady state experimental landscapes. Our experiments generate power law distributions of landslide sizes, somewhat similar to both field and laboratory observations. Thus even a simple model of bedrock landsliding is capable of quantitatively reproducing mountainous topography and landslide distributions and represents a significant step forward in our understanding of the evolution of normal-fault-bounded ranges.