Movement monitoring and runout simulations of the Gold Basin landslide complex using LiDAR, SAR, and numerical models

Abstract:

A landslide complex at Gold Basin, along the South Fork Stillaguamish River in northwestern Washington, has drawn considerable attention after a catastrophic runout of the nearby landslide at Oso, Washington, in 2014. Of particular concern near the Gold Basin site is a popular campground situated on the flood plain across the river from the toe of the slide. To evaluate potential threats to the campground, we integrated multi-source remote sensing and numerical models to monitor recent landslide activity and simulate hypothetical runout scenarios. Bare-earth lidar DEM (Digital Elevation Model) differencing, InSAR (Interferometric Synthetic Aperture Radar), and offset tracking of SAR images reveal that localized collapses at the headscarp have been the primary type of landslide activity at Gold Basin from 2005 to 2019. Currently there are no signs indicative of movement of a large centralized block or a deep-seated main body. The maximum rate of surface displacement is 5 m/yr, occurring primarily from headscarp recession near the centerline of the three-lobed complex. The annual landsliding volume of the whole landslide complex averages 1.03×10⁵ m³. The maximum possible landslide volume is estimated as 2.0×10⁶ m³ from three-dimensional limit equilibrium analysis of generalized terrace structures. Using these landslide source geometry constraints, we simulated a range of hypothetical runout scenarios using the depth-averaged two-phase model D-Claw. The simulation results demonstrate that runout from initial sources with volumes less than 10⁵ m³ pose only limited threats to the campground, while initial source volumes over 10⁶ m³ could cause severe damages. Consequently, the estimated maximum landslide volume of 2.0×10⁶ m³ suggests a potential risk to the campground nearby. Adaption of our methodology could prove useful for evaluating other similar landslides for hazards prevention and mitigation.