Outbursts From an Ice-Dammed Lake: A Collaborative Study

Anderson OPP-99-12129喷泉OPP-99-12180 Walder OPP-99-12306这是一项合作研究，包括波特兰州立大学、美国地质调查局和加州大学圣克鲁斯分校。当冰坝水体突然排干时，就会发生暴发洪水。这些洪水可能会对下游产生毁灭性的影响。它们可以戏剧性地重塑河道，并可能对人类住区构成威胁。由于突发性洪水是不可预测的，对蓄水储存和释放的机制(突发性洪水的时间、大小和地貌效应)研究得很少。我们所知道的主要来自冰岛的观测，那里的冰下和冰缘湖泊定期排水。在其他地方，观察结果是偶然的或事后的。首席调查人员将调查兰格尔-圣彼得堡肯尼科特冰川上可预测的年度喷发地点。阿拉斯加的伊莱亚斯国家公园。冰缘隐溪湖的排水危及附近居民和国家公园的游客。首席调查人员将检查引发洪水的突发事件，开始测试和完善现有的理论模型。他们的假设是，冰坝不会形成因漂浮而突然破裂的“紧密”液压密封。相反，随着湖泊水位的上升，它最初会连接到一个分布式的基础排水系统，导致缓慢而稳定的泄漏。最终，湖面上升到足够高的程度，与远离冰川边缘的树状渠道网络建立了水力连接。然后，湖水迅速排干，这可能与管道系统的季节性发展或冰川激增的终止状态有关。该提案对实地工作有四个主要目标：1)测量湖水充盈和排空时的冰坝变形，并表征冰坝的机械行为；2)测量湖面随时间的变化，确定湖泊的水位变化，并测量湖泊的热结构。3)检查冰坝的水力完整性和使用钻孔的冰下排水系统的时间变化；以及4)监测靠近冰川末端的出口河流的洪水和河道形态的变化。

AbstractAnderson OPP-99-12129Fountain OPP-99-12180Walder OPP-99 -12306This is a collaborative study which includes Portland State University, the U.S. Geological Survey, and University of California, Santa Cruz. Outburst floods, or jokulhlaups, occur when ice-dammed water bodies drain suddenly. These floods can have devastating downstream effects. They can dramatically reshape stream channels and can be a hazard to human settlements. The mechanisms (timing, size, and geomorphic effect of outburst floods) by which impounded water is stored and released have been poorly studied because outburst floods are unpredictable. What is known comes primarily from observations in Iceland where subglacial and ice marginal lakes drain periodically. Elsewhere, observations have been serendipitous or after the fact. The Principal Investigators will investigate a site with predictable, annual outbursts on the Kennicott Glacier in Wrangell-St. Elias National Park, Alaska. The drainage of ice-marginal Hidden Creek Lake endangers nearby residents and visitors to the National Park.The Principal Investigators will examine outburst flood triggering to begin testing and refining existing theoretical models. Their hypothesis is that the ice dam does not form a "tight" hydraulic seal that is abruptly broken by flotation. Instead, as the lake level rises, it initially becomes connected to a distributed basal drainage system resulting in a slow, stable leak. The lake level eventually rises enough that hydraulic connection is established with an arborescent channel network away from the edge of the glacier. The lake then drains rapidly, and may be related to seasonal development of a conduit system or to the termination state of a glacier surge.The proposal has four main goals to the field work: 1) to measure ice-dam deformation as the lake fills and empties and characterize how the ice dam behaves mechanically; 2) to measure lake level as a function of time, determine lake hypsometry, and measure the lake's thermal structure. 3) to examine the hydraulic integrity of the ice dam and temporal changes in the subglacial drainage system using boreholes; and 4) to monitor the flood and changes in channel morphology in the outlet river near the glacier terminus.