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首页> 外文期刊>Earth Surface Processes and Landforms: The journal of the British Geomorphological Research Group >Large wood inhibits debris flow runout in forested southeast Alaska
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Large wood inhibits debris flow runout in forested southeast Alaska

机译：大木材抑制阿拉斯加森林东南部的碎片流动跳动

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摘要

Due to their potentially long runout, debris flows are a major hazard and an important geomorphic process in mountainous environments. Understanding runout is therefore essential to minimize risk in the near-term and interpret the pace and pattern of debris flow erosion and deposition over geomorphic timescales. Many debris flows occur in forested landscapes where they mobilize large volumes of large woody debris (LWD) in addition to sediment, but few studies have quantitatively documented the effects of LWD on runout. Here, we analyze recent and historic debris flows in southeast Alaska, a mountainous, forested system with minimal human alteration. Sixteen debris flows near Sitka triggered on August 18, 2015 or more recently had volumes of 80 to 25 000 m(3) and limited mobility compared to a global compilation of similarly-sized debris flows. Their deposits inundated 31% of the planimetric area, and their runout lengths were 48% of that predicted by the global dataset. Depositional slopes were 6 degrees-26 degrees, and mobility index, defined as the ratio of horizontal runout to vertical elevation change, ranged from 1.2 to 3, further indicating low mobility. In the broader southeast Alaskan region consisting of Chichagof and Baranof Islands, remote sensing-based analysis of 1061 historic debris flows showed that mobility index decreased from 2.3-2.5 to 1.4-1.8 as average forest age increased from 0 to 416 years. We therefore interpret that the presence of LWD within a debris flow and standing trees, stumps, and logs in the deposition zone inhibit runout, primarily through granular phenomena such as jamming due to force chains. Calibration of debris flow runout models should therefore incorporate the ecologic as well as geologic setting, and feedbacks between debris flows and vegetation likely control the transport of sediment and organic material through steep, forested catchments over geomorphic time. (c) 2020 John Wiley & Sons, Ltd.
机译：由于他们潜在的长跳动，碎片流动是山区环境中的主要危害和重要的地貌过程。因此，了解跳动对于最大限度地减少近期风险并解释碎片流动侵蚀和沉积在几何时间尺度上的速度和模式。许多碎片流动发生在森林景观中，除沉积物之外，他们还会调动大量的大型木质碎片（LWD），但很少有研究表明LWD对跳动的影响。在这里，我们分析了阿拉斯加东南部的最近和历史碎片，一个山区，森林制度，具有最小的人类改变。与同类碎片流动的全球汇编相比，2015年8月18日或者最近在2015年8月18日或最近拥有80至25000米（3）卷，并且相比，迁移率为80至25 000米（3）的数量。他们的存款淹没了31％的平面图，它们的跳动长度为全球数据集预测的48％。沉积斜率为6摄氏度 - 26度，移动性指数，定义为水平跳动与垂直升高变化的比率，范围为1.2至3，进一步表明低迁移率。在由ChichaGof和Baranof岛组成的更广泛的东南部地区，对1061历史碎片流动的遥感分析表明，随着平均森林年龄从0到416年增加，移动指数从2.3-2.5降至1.4-1.8。因此，我们解释了碎屑流动和常设树木，树桩和沉积区的常设树木，树桩和日志中的LWD的存在，主要通过粒状现象，例如由于力链而发生干扰。因此，碎屑流动跳动模型的校准应该将生态和地质设置纳入，并且通过陡峭的森林集水区在地貌时间上通过陡峭，泥土流量和植被之间的反馈可能控制沉积物和有机材料的运输。 （c）2020 John Wiley＆Sons，Ltd。

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