Geomorphology and initiation mechanisms of the 2020 Haines, Alaska landslide

In early December 2020, an atmospheric river (AR) and rain-on-snow (ROS) event impacted the Haines, Alaska area, resulting in record-breaking rainfall and snowmelt that caused flooding and dozens of mass movement events. We consider the AR-a one-in-500-year event-as the trigger for the devastating Beach Road Landslide (BRLS), which destroyed or damaged four residences and took the lives of two people. The BRLS started as a debris avalanche and transitioned into a debris flow, with a total approximate landslide volume of 187,100 m(3). Geomorphic analysis using lidar data identified evidence of paleo-landslides and displaced masses of rock, one of which served as the source area for the BRLS. Significant structural features in the weak ultramafic bedrock defined the head scarp area and formed the failure plane. This study illustrates the importance of identifying pre-existing landslide features and source areas likely to produce future landslides. As an increase in ROS events is projected for Southeast Alaska with warmer and wetter winters, we recommend the development of an AR scale coupled with geological information for the region, to enhance warnings to residents in landslide-prone areas.

Automated summary

In early December 2020, an extreme weather event consisting of an atmospheric river and rain-on-snow caused flooding and mass movement in Haines, Alaska. The event, which was considered a one-in-500-year occurrence, triggered a devastating landslide that resulted in casualties and property damage. The study highlights the importance of identifying pre-existing landslide features and potential source areas for future landslides. With projections of increased similar events in Southeast Alaska due to warmer and wetter winters, the development of an AR scale combined with geological information is recommended for better warning systems.