Large wood inhibits debris flow runout in forested southeast Alaska
Large wood inhibits debris flow runout in forested southeast Alaska
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DOI：
10.1002/esp.4830
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发表时间：
2020-02-26
影响因子：
3.3
通讯作者：
Buma, Brian
中科院分区：
文献类型：
--
作者：
Booth, Adam M.;Sifford, Christian;Buma, Brian
由于其潜在的长径流，泥石流是一个重大的危险，在山区环境中的一个重要的地貌过程。因此，了解跳动是至关重要的，以尽量减少风险，在短期内和解释的速度和模式的泥石流侵蚀和沉积的地貌时间尺度。许多泥石流发生在森林景观，他们动员大量的大型木质残体（LWD）除了沉积物，但很少有研究定量记录LWD对径流的影响。在这里，我们分析了最近和历史上的泥石流在阿拉斯加东南部，一个山区，森林系统与最小的人类改变。2015年8月18日或最近在锡特卡附近触发的16个泥石流的体积为80至25000 m（3），与全球类似规模的泥石流汇编相比，流动性有限。它们的沉积物淹没了31%的平面面积，其流出长度是全球数据集预测的48%。沉积坡度为6度-26度，流动性指数（定义为水平跳动与垂直高程变化的比值）为1.2 - 3，进一步表明流动性较低。在更广泛的阿拉斯加东南部地区组成的Chichagof和Baranof群岛，遥感为基础的分析1061历史泥石流表明，流动性指数从2.3-2.5下降到1.4-1.8平均林龄从0增加到416年。因此，我们解释说，随钻测井的存在下，泥石流和站立的树木，树桩，并在沉积区的日志抑制跳动，主要是通过颗粒现象，如堵塞由于力链。因此，泥石流径流模型的校准应包括生态和地质背景，泥石流和植被之间的反馈可能控制沉积物和有机物质通过陡峭的，森林覆盖的集水区在地貌时间的运输。(c)2020约翰威利父子有限公司
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.