Climatic and Geomorphic Triggering Mechanisms of Cascadian Periglacial Debris Flows

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。在喀斯喀特成层火山冰川山谷上游发起的泥石流通常与亚热带急流带来的强烈多日降雨事件有关。最近的调查表明，这种雨致泥石流的数量和规模可能正在增加，这表明它们可能受到气候变化的影响。研究的总体目标是利用气候和地貌的观点来描述太平洋西北部这些冰缘泥石流的触发机制。目标研究区域是俄勒冈州的胡德山和华盛顿的雷尼尔山，但这项研究广泛适用于太平洋西北部其他复合火山的泥石流。具体目标是：1.绘制冰缘泥石流的初始位置图并描述其特征;2.绘制和量化过去几十年来雷尼尔山和胡德山冰川面积的年度变化;3.对过去几十年来造成冰缘泥石流的风暴进行定性和分类;4.量化泥石流的前期条件，包括降雨和积雪;5.了解近期泥石流背景下泥石流的历史记录;6.发展和评估降雨引起的冰缘泥石流的预报方案。本研究采用了基于广泛的观察证据的经验方法。将使用实地调查、机载激光雷达图像和航空照片绘制起始地点的地图和特征。将利用30米陆地卫星图像（1984年至今）和以前出版的冰川图绘制冰川范围和面积的年度变化图。泥石流清单将用于与具体的风暴事件和先前条件相匹配。将使用各种来源的气象数据来确定风暴方向、综合水汽输送、降雨强度、风暴冻结高度、积雪和以往降雨量的特征。泥石流的历史背景将利用从航空照片和地貌和树木年代学数据从实地调查中开发的年表进行探索。使用我们的风暴和启动网站的定量表征，我们将开发一个类型的网站和情况下，是很重要的触发雨引起的泥石流。这种冰缘泥石流（“山体滑坡”）对该地区的基础设施是毁灭性的，因为它们摧毁了道路、桥梁、建筑物、露营地、小径和灌溉设施。在2006年11月的一次特别大的事件之后，雷尼尔山国家公园不得不前所未有地关闭了六个月;仅公园就遭受了近3000万美元的损失。风暴引发的泥石流摧毁了胡德山（Mount Hood）怀特河（White River）排水系统的一座主要桥梁和道路，导致该地区最重要的滑雪场之一的开放延迟数周;在艾略特（Eliot）排水系统，中叉灌溉区（Middle Fork Irrigation District）由于泥石流风险高，无法再为引水结构投保。从长远来看，这些泥石流和洪水携带的沉积物沉积在河床中，使河床抬高，随后的泥石流更容易造成大洪水。此外，冰川的消退使更多的沉积物暴露出来，这些沉积物具有侵蚀性。这就提出了这样的问题：泥石流是否会变得更加普遍，它们是否会携带更大体积的沉积物更远的距离？确定风暴类型和发生地点的特征将为风险评估提供科学依据，从而有助于决策者。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Debris flows initiating in the upper reaches of glaciated valleys of the Cascade stratovolcanoes are typically associated with intense, multi-day rain events being brought in by the subtropical jet stream. Recent investigations suggest that the number and size of such rain-induced debris flows may be on the increase, which indicates that they may be affected by climate change. The overall goal of the research is to characterize the triggering mechanisms of these periglacial debris flows in the Pacific Northwest using both climate and geomorphic perspectives. The targeted study areas are Mount Hood, Oregon and Mount Rainier, Washington but the research is broadly applicable to debris flows on other composite volcanoes in the Pacific Northwest. The specific objectives are to: 1. Map and characterize the initiation sites of rain-induced periglacial debris flows;2. Map and quantify annual changes in glacier area on Mount Rainier and Mount Hood over the past several decades;3. Characterize and classify the storms that have caused recent periglacial debris flows over the past several decades;4. Quantify antecedent conditions for debris flows including rainfall and snow cover;5. Understand recent debris flows in the context of debris flows over the historic record;6. Develop and evaluate prognostic schemes for rain-induced periglacial debris flows. This research employs an empirical approach based on a wide range of observational evidence. The initiation sites will be mapped and characterized using field surveys, airborne LiDAR imagery, and aerial photos. Annual changes in glacier extent and area will be mapped using 30-m Landsat satellite imagery (1984-present) and previously published glacier maps. The inventory of debris flows will be used to match with specific storm events and antecedent conditions. Meteorological data from various sources will be used to characterize storm direction, integrated water vapor transport, rainfall intensity, storm freezing altitude, snow cover, and previous rainfall amounts. Historic context of debris flows will be explored using chronologies developed from aerial photos and geomorphic and dendrochronologic data from field surveys. Using our quantitative characterizations of storms and initiation sites we will then develop a typology of sites and circumstances that are important in triggering rain-induced debris flows. Such periglacial debris flows ("landslides") are devastating to infrastructure in the region as they wipe out roads, bridges, buildings, campgrounds, trails, and irrigation facilities. After a particularly large number of these in November 2006 event, Mount Rainier National Park had to be closed for an unprecedented six months; the park alone suffered nearly $30M in damage. At Mount Hood, debris flows from this storm destroyed a major bridge and road in the White River drainage causing a multi-week delay in opening one of the premier ski areas in the region; in the Eliot drainage, the Middle Fork Irrigation District is no longer able to insure their water diversion structures because of the high risk of debris flows. Of longer-term concern, the sediment carried by these debris flows and floods is deposited in the streambed, which raisies the streambed elevation and subsequent flows will more readily result in major flooding. In addition, the receding glaciers on expose more sediment capable of erosion. This raises such questions as: will debris flows become more common and will they carry larger volumes of sediment longer distances? Characterizing both the storm type and the initiation sites will aid decision makers by providing a scientific basis for risk assessment.