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多天强降雨事件有关。最近的调查表明，这种由降雨引发的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。这项研究的总体目标是从气候和地貌两个角度描述太平洋西北部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上的泥石流。具体目标是：1.绘制降雨引起的冰川泥石流的起始点的地图并确定其特征；2.绘制过去几十年来雷尼尔山和胡德山冰川面积的年度变化地图并加以量化；3.确定过去几十年来造成最近冰川泥石流的风暴的特征和分类；4.量化泥石流的前期条件，包括降雨和积雪；5.从历史记录上的泥石流情况了解最近的泥石流；6.制定和评估降雨引起的冰川周围泥石流的预报方案。这项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启动点的地图并确定其特征。冰川范围和面积的年度变化将使用30米长的陆地卫星图像(1984年至今)和以前公布的冰川地图绘制。泥石流清单将用于与具体的风暴事件和之前的条件相匹配。来自不同来源的气象数据将被用来描述风暴方向、综合水汽输送、降雨强度、风暴冰冻高度、积雪和以前的降雨量。将利用根据航空照片编制的年表以及来自实地调查的地貌和树状年代学数据来探讨泥石流的历史背景。然后，利用我们对风暴和起始点的定量描述，我们将制定对引发降雨引起的泥石流很重要的地点和环境的类型学。这种冰缘泥石流(“山体滑坡”)摧毁了道路、桥梁、建筑物、露营地、步道和灌溉设施，对该地区的基础设施造成了毁灭性的破坏。雷尼尔山国家公园在2006年11月发生了一次特别多的此类事件后，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，这场风暴的泥石流摧毁了怀特河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区之一的开放延迟了数周；在艾略特排水系统，中福克灌区由于泥石流的高风险，不再能够为其引水结构提供保险。更长远的问题是，这些泥石流和洪水携带的泥沙沉积在河床中，使河床水位升高，随后的水流将更容易导致重大洪灾。此外，正在消退的冰川暴露出更多可能被侵蚀的沉积物。这引发了这样的问题：泥石流会变得更加常见吗？它们会携带更多的泥沙走更远的距离吗？确定风暴类型和起始点的特征将为风险评估提供科学依据，从而帮助决策者。

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.