Devil's Slide: An Evolving Feature of California's Coastal Landscape

Abstract

Coastal landslides in the United States remain a persistent threat to human life and urban development. The focus of this study is a landslide-prone section of the central California coastline, approximately 20 km south of San Francisco, known as Devil9s Slide. This investigation employs an extensive aerial image inventory, digital elevation models (DEMs), and a water balance/limit-equilibrium approach to better understand the spatial and temporal characteristics of deep-seated bedrock slides at the site. Photographic surveys of the area reveal nearly 3 km of headscarp and a complex network of slope failures that respond to hydrologic, seismic, and anthropogenic perturbations. DEM analysis suggests that for a 145-year period (1866 to 2010), the study area experienced an average coastal retreat rate of 0.14 m/yr and an average volumetric loss of 11,216 m 3 /yr. At least 38 percent of the landscape evolution in the steep coastal terrain has been driven by slope failure events. A loosely coupled water balance/limit-equilibrium analysis quantitatively illustrates the precarious nature of the active landslide zone at the site. The slope is shown to be unstable for a large suite of equally likely scenarios. The analyses presented herein suggest that future work should include a rigorous characterization of pore-water pressure development, driven by comprehensive simulations of subsurface hydrologic response, to improve our understanding of slope failure initiation at the Devil9s Slide site.