The Preservation of Climate‐Driven Landslide Dams in Western Oregon. Issue 4 (18th April 2021)

• Record Type: Journal Article
• Authors: Struble, William T.; Roering, Joshua J.; Burns, William J.; Calhoun, Nancy C.; Wetherell, Logan R.; Black, Bryan A.
• Is Part Of: Journal of geophysical research. Volume 126:Issue 4(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-04-18
• Subjects: cascadia -- dendrochronology -- ghost forests -- lakes -- landslides; Geomorphology -- Periodicals; 551.3
• DOI: 10.1029/2020JF005908
• Languages: English
• ISSNs: 2169-9003

Abstract

Abstract: Bedrock landsliding, including the formation of landslide dams, is a predominant geomorphic process in steep landscapes. Clarifying the importance of hydrologic and seismic mechanisms for triggering deep‐seated landslides remains an ongoing effort, and formulation of geomorphic metrics that predict dam preservation is crucial for quantifying secondary landslide hazards. Here, we identify >200 landslide‐dammed lakes in western Oregon and utilize dendrochronology and enhanced 14 C dating ("wiggle matching") of "ghost forests" to establish slope failure timing at 20 sites. Our dated landslide dataset reveals bedrock landsliding has been common since the last Cascadia Subduction Zone earthquake in January 1700 AD. Our study does not reveal landslides that date to 1700 AD. Rather, we observe temporal clustering of at least four landslides in the winter of 1889/1890 AD, coincident with a series of atmospheric rivers that generated one of the largest regionally recorded floods. We use topographic and field analyses to assess the relation between dam preservation and topographic characteristics of the impounded valleys. In contrast to previous studies, we do not observe systematic scaling between dam size and upstream drainage area, though dam stability indices for our sites correspond with "stable" dams elsewhere. Notably, we observe that dams are preferentially preserved at drainage areas of ∼1.5 to 13 km 2 and valley widths of ∼25 to 80 m, which may reflect the reduced downstream influence of debris flows and the accumulation of mature conifer trees upstream from landslide‐dammed lake outlets. We suggest that wood accumulation upstream of landslide dams tempers large stream discharges, thus inhibiting dam incision. Key Points: New 20 landslide dam ages in the Oregon Coast Range record persistent bedrock landsliding since the last earthquake in 1700 AD At least four dams temporally cluster in the winter 1889/1890, potentially coincident with flooding in February 1890 from atmospheric rivers Landslide dams preferentially preserved at particular drainage areas and valley widths. Large wood may inhibit dam incision