Deep-seated, bedrock landslides are common throughout the Oregon Coast Range (greater than 20,000 have been mapped to date). While it was oft assumed that most bedrock landslides in Cascadia are triggered by Cascadia Subduction Zone earthquakes, no landslide has been definitively linked with the last major earthquake, which occurred on January 26, 1700. Dendrochronology of drowned “ghost forests” at landslide-dammed lakes allows for seasonally accurate dating and clearer interrogation of seismic and hydrologic triggering mechanisms. Those temporal data of landslide dam triggering can then be used to identify geomorphic factors (e.g., drainage area, valley width, large wood) that dictate landslide dam stability over a range of timescales.
Struble W (2022) Seismic vs. hydrologic triggering of landslide dams in the Oregon Coast Range. USGS Landslide Hazards Seminar, 9 February 2022.
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