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。起源于喀斯喀特层状火山冰川山谷上游的泥石流通常与副热带急流带来的强烈的、多日的降雨事件有关。最近的调查表明，这种降雨引起的泥石流的数量和规模可能在增加，这表明它们可能受到气候变化的影响。该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地区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州的雷尼尔山，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。2.绘制雨致冰缘泥石流起爆地点的地图和特征；2 .绘制和量化过去几十年雷尼尔山和胡德山冰川面积的年变化；3 .对过去几十年来造成最近冰周泥石流的风暴进行特征描述和分类；4 .量化泥石流的先决条件，包括降雨和积雪；5 .在泥石流历史记录的背景下理解最近的泥石流；制定和评估降雨引起的冰缘泥石流的预报方案。本研究采用基于广泛观察证据的实证方法。启动地点将使用实地调查、机载激光雷达图像和航空照片进行测绘和表征。冰川范围和面积的年变化将利用30米陆地卫星图像（1984年至今）和以前出版的冰川地图绘制。泥石流的清单将用于与特定的风暴事件和先前的条件相匹配。来自不同来源的气象数据将用于描述风暴方向、综合水汽输送、降雨强度、风暴冻结高度、积雪和以前的降雨量。泥石流的历史背景将利用从航空照片和从实地调查中获得的地貌和树木年代学数据开发的年代学来探索。利用我们对风暴和起始地点的定量描述，我们将开发一个对触发降雨引发的泥石流很重要的地点和环境的类型学。这种冰川周围的泥石流（“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月发生了大量此类事件后，雷尼尔山国家公园不得不史无前例地关闭了6个月；仅该公园就遭受了近3000万美元的损失。在胡德山，风暴带来的泥石流摧毁了怀特河流域的一座主要桥梁和道路，导致该地区一个主要滑雪场的开放推迟了数周；在艾略特流域，由于泥石流的高风险，中叉灌区不再能够为其引水结构提供保险。从长远来看，这些泥石流和洪水所携带的沉积物会沉积在河床上，从而提高河床的高度，随后的水流更容易导致大洪水。此外，退缩的冰川暴露出更多能够侵蚀的沉积物。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到更远的地方？确定风暴类型和起爆地点将为决策者提供科学的风险评估依据。

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.