EXPLORING THE INFLUENCE OF LARGE LANDSLIDES ON RIVER INCISION AND LANDSCAPE EVOLUTION

Large landslides are a prominent feature of hillslope erosion in steep, actively incising landscapes around the world, yet few models of bedrock river incision and landscape evolution allow for dynamic feedbacks between river incision and the influence of large landslides. In our presentation, we discuss field examples from the eastern margin of the Tibetan plateau that highlight the interaction between landslide dams, channel morphology, longitudinal river profiles, and river incision. These field examples show that over time-scales relevant to landscape evolution (>10,000 yr), large landslides can inhibit incision and prevent the complete adjustment of rivers to regional tectonic, climatic and lithologic forcing. We use these observations to motivate and formulate a simple, probabilistic, numerical model that provides a quantitative framework for evaluating how landslides influence river incision and landscape evolution in general. Stable landslide dams create mixed bedrock-alluvial channels that reduce the total amount of incision occurring over a given length of river, ultimately slowing long-term rates of river incision. The magnitude of this landslide influence is determined by the time-average number of landslide dams along a river course, which is governed by two fundamental timescales: the time it takes to erode landslide deposits and erase individual dams; and the recurrence interval of large landslides that lead to stable dams. We discuss the variables that affect these timescales and use them to derive a coefficient of river incision efficiency which speaks to the spatial and temporal intermittency of incision due to the effects of stable landslide dams.