Feedbacks between river meandering and landsliding in northwestern Washington glacial outwash terraces

Landslides that occur in river valleys can be large, highly mobile, and cause cascading downstream hazards associated with landslide dams and elevated flood risk. However, the role of rivers in triggering landslides is not well understood: are there spatial and temporal patterns in river geometry leading up to major landslide events? Additionally, how does river geometry respond to deep-seated landsliding?

This talk investigates river-landslide feedbacks in the Nooksack River in western Washington State where the channel is flanked by landslide-prone glacial terraces that are similar to those that failed in the deadly 2014 Oso landslide. We show that landsliding and river meandering can be dynamically coupled: deep-seated landslides can “push” the river away from the floodplain margin, creating a new up- or downstream river meander. This new meander erodes the adjacent terrace, triggering a secondary landslide. This conceptual model has ramifications for improving hazard management in river corridors as well as informing fundamental understandings of the river-hillslope interface in landscape evolution.