Coupling between Co-seismic Landslides and Landscape Evolution in Active Orogenic Belts

Concentration of 10Be in detrital quartz from river sediments is widely used to quantify catchment-wide denudation rates and reconstruct tectonic history. This method basically presumes a steady state in the removal of surface materials. However, in active orogenic belts, co-seismic landslides extensively occur in shaping the landscape, and the contribution of debris from bedrock zone significantly dilutes the 10Be concentration in river sediments, which leads an overestimation of the denudation rates. The disruption of the steady state with the dilution effect caused by earthquake-induced catastrophic landslides remains unclear, especially for its implications on evolution of mountainous landscapes. This study aimed to investigate: 1) topographic features of an active orogenic belt after a catastrophic earthquake; 2) indications of catchment-wide 10Be concentrations in river sediments; and 3) the relationships between spatial distribution pattern of co-seismic landslides, geomorphic metrics, and detrital 10Be abundance.

Our work was conducted in the upstream Minjiang catchment, eastern margin of the Tibetan Plateau. Various geomorphic indices were extracted via analyses of a digital elevation model (DEM). Published inventories of co-seismic landslides by the Wenchuan Earthquake in 2008 were compiled to derive landslide area percentage (LAP). Fluvial stream sands were sampled at outlet of catchments under varying effects of the co-seismic landsliding.

Our results suggest that topography meet a threshold in both landslide-affected area and non-landsliding area. However, the variation in 10Be concentrations and topographic proxies in these two areas show different trends. In the landslide-affected area, presence of substantial co-seismic landslides complicates the relationship between landscape and 10Be concentrations. The contribution of co-seismic landslides to the landscape evolution process seems more pronounced in mid-relief areas.