CHARACTER AND DYNAMICS OF CREEPING LANDSLIDES ALONG THE U.S. WEST COAST

Slow-moving landslides are an important landscape shaper and pose a dangerous natural hazard around the globe. Better understanding the character and dynamics of these slowly deforming hillslopes lights the way to mitigate their hazards. Toward this objective, we utilize L-band InSAR (Interferometric Synthetic Aperture Radar) deformation maps from 2007 to 2019 to systematically map large, mobile landslides across the U.S. West Coast, and investigate how geologic settings intrinsically control the landslide character. Using the identified 617 active slides, we find that slow-moving landslides are generally larger and more spatially frequent in homogeneous bedrock with low rock strength, and they are preferentially located on hillslopes with geologically recent uplift. Next, we focus on the temporal kinematics of three creeping landslides. By utilizing space geodesy to obtain multi-year deformation time series of these slow-moving landslides (e.g., the Oak Ridge slide in California, the Hooskanaden slide in Oregon, and the Locke slide in Washington), we find that their dynamics differs drastically depending on the nature of the dominant external forcing (e.g., seasonal precipitation, coastal erosion, agricultural irrigation, and river level fluctuation). The knowledge obtained from these case studies could prove useful for landslide characterization and hazard reduction beyond the regional scale.