Portland State University. Department of Geology
Term of Graduation
Date of Publication
Master of Science (M.S.) in Geology
1 online resource (viii, 84 pages)
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 continued interest to the Oregon Department of Transportation (ODOT) 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 (El Niño Southern Oscillation, and Pacific Decadal Oscillation), manual feature tracking on orthorectified aerial photographs and satellite images from PlanetLabs was used to create a surface velocity time series from 1980 to late 2019. In comparing our velocity time series to local precipitation records over the same period, it is clear that periods of seasonal acceleration correspond with above average precipitation. However, periods of surging did not correspond to years with the highest seasonal precipitation, although they do appear to correlate with transitions between warm and cold phase climate cycles. Additionally, extensive surface mapping and carbon dating were performed to understand the morphology and origins of this landslide. Logs exposed by erosion at the toe of the landslide were sampled and used for radiocarbon dating and 14C wiggle matching. Sample calendar age ranges were constrained using stratigraphic and varve models within OxCal Bayesian statistical modeling software. Based on agreement between multiple age models from two sets of samples, we estimate that this slide has been active since ~1770 AD -- several decades after the last Cascadia Subduction Zone earthquake. While this suggests that the initial failure was not coseismic, it is possible that seismic stresses may have weakened the basal plane to allow for future failure. Mitigating landslide hazards requires knowledge of landslide kinematics and behavior over decadal to century timescales. The findings of this study can be used to better predict and plan for future surge events â€“ which will likely continue to occur.
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Kingen, Kara, "Climatic Controls on the Kinematics of the Hooskanaden Landslide, Curry County, Oregon" (2021). Dissertations and Theses. Paper 5678.