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The Preservation of Climate‐Driven Landslide Dams in Western Oregon
Journal of Geophysical Research: Earth Surface ( IF 3.9 ) Pub Date : 2021-03-19 , DOI: 10.1029/2020jf005908
William T. Struble 1, 2 , Joshua J. Roering 1 , William J. Burns 3 , Nancy C. Calhoun 3 , Logan R. Wetherell 1 , Bryan A. Black 4
Affiliation  

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 14C 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 km2 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.

中文翻译:

俄勒冈州西部气候驱动的滑坡坝的保护

基岩滑坡,包括滑坡坝的形成,是陡峭景观中的主要地貌过程。澄清水文和地震机制对于引发深部滑坡的重要性仍在持续进行,而预测大坝保护的地貌指标的制定对于量化次生滑坡灾害至关重要。在这里,我们确定了俄勒冈州西部的200多个滑坡坝湖泊,并利用树状年代学和增强的“鬼林”的14 C年代(“摆动匹配”)来确定20个地点的边坡破坏时间。我们的日期滑坡数据集显示,自公元1700年1月的上一次卡斯卡迪亚俯冲带地震以来,基岩滑坡一直很普遍。我们的研究没有揭示可追溯至公元1700年的滑坡。相反,我们观察到了时间的聚类至少在1889/1890 AD的冬天发生了四次滑坡,与一系列大气河流重合,这些河流产生了最大的区域性洪灾之一。我们使用地形和野外分析来评估大坝保护与蓄积山谷地形特征之间的关系。与以前的研究相比,尽管我们站点的大坝稳定性指标与其他地方的“稳定”大坝相对应,但我们并未观察到大坝尺寸与上游流域之间的系统缩放。值得注意的是,我们观察到大坝优先保留在1.5至13 km 2的流域和约25至80 m的谷宽,这可能反映了泥石流对下游的影响减小以及滑坡筑坝的湖泊出口上游成熟的针叶树的堆积。我们建议,滑坡水坝上游的木材积聚会抑制大流量的水流,从而抑制水坝的切割。
更新日期:2021-04-19
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