Characterizing the catastrophic 2017 Mud Creek Landslide, California, using repeat Structure-from-Motion (SfM) photogrammetry

Along the rugged coast of Big Sur, California, the Mud Creek landslide failed catastrophically on May 20, 2017 and destroyed over 400 m of scenic California State Highway 1. We collected structure-from-motion (SfM) photogrammetry data using airborne platforms that, when combined with existing airborne lidar data, revealed that the area exhibited significant topographic change and displacement before, during and after the catastrophic failure. Before the catastrophic failure we document two areas of elevated change in the zone of depletion, which aligned with the double-peaked head scarp produced by the catastrophic failure. The catastrophic failure extended from 337 m elevation to at least 8 m below sea level, was 490 m wide, displaced ~3 million m3 of earth and rock, and deposited landslide debris at least 175 m seaward of the original shoreline. The failure was not a complete slope-clearing event, however, and several upslope and lateral regions that did not slip into the ocean exhibited significant displacement and topographic change during the days and months after catastrophic failure. Additionally, we use the post-slide data to quantify several other processes, including the time-varying rates of talus accumulation and coastal erosion of the landslide toe. We conclude that repeat SfM surveys from aerial imagery can provide valuable information about landslide evolution and the potential for deep-seated landslide hazards – especially in the lead up to catastrophic failure – if photos are collected and processed regularly.