Climatic Controls on the Kinematics of the Hooskanaden Landslide, Curry County, Oregon

Kingen, Kara, Portland State University, kkingen@pdx.edu; Adam Booth, boothad@pdx.edu; Ben Leshchinsky, Ben.Leshchinsky@oregonstate.edu (Poster)

Slow-moving earthflows represent major sources of sediment transport and erosion and are problematic for the management of critical infrastructure. The Hooskanaden Landslide—a slow-moving earthflow on the southwest coast of Oregon—crosses US Highway 101 and has been a site of particular interest to the Oregon Department of Transportation due to the weak lithology, erosive environment, and recurrent surge behavior (every ~15 years). Past surges, including the most recent (2019), have occurred during the winter, suggesting that velocity changes are predominantly controlled by climatic inputs. To examine the response of the Hooskanaden Landslide to seasonal and other periodic climate cycles (such as El Niño–Southern Oscillation), manual feature tracking on satellite images from PlanetLabs was used to create a surface velocity time series from 2009 to late 2019. In comparing our velocity time series to precipitation records from the area, it is clear that periods of seasonal acceleration correspond with above average precipitation. However, surges did not correspond to years with the highest seasonal precipitation, although they did correlate with El Niño years. Additionally, extensive surface mapping and carbon dating were performed to understand the morphology and origins of this landslide. Three tree rounds were cut from logs previously buried at the toe of the landslide and subsequently exposed by erosion for radiocarbon analysis using wiggle matching. Possible ages of samples were constrained using stratigraphic, dendrochronological, and varve models within OxCal. Based on agreement between multiple calibration models over two sets of samples, we estimate that this slide has been active since ~1750 AD—several decades after the last Cascadia Subduction Zone earthquake. Given its age, measurable annual displacements, cyclic surge behavior, and continuous erosion at the toe, it is likely that this earthflow will continue to be active for the foreseeable future.

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