Outbursts from an Ice-Dammed Lake: A Collaborative Study

这是一项合作研究，包括波特兰州立大学、美国地质调查局和圣克鲁斯的加州大学。 当冰坝的水体突然流失时，就会发生爆发性洪水。这些洪水可能对下游造成破坏性影响。 它们可以极大地改变河道，并可能对人类住区造成危害。 由于突发洪水是不可预测的，因此对蓄水储存和释放的机制（突发洪水的时间、规模和地貌效应）的研究很少。 我们所知道的主要来自冰岛的观测，那里的冰下湖和冰缘湖定期排水。 在其他地方，观察是偶然的或事后的。 主要调查人员将调查阿拉斯加兰格尔-圣埃利亚斯国家公园肯尼科特冰川上一个可预测的年度喷发地点。 冰缘隐溪湖的排水危及附近居民和国家公园的游客。主要研究人员将研究突发洪水触发，开始测试和完善现有的理论模型。 他们的假设是，冰坝并没有形成一个“紧密”的液压密封，这是突然打破漂浮。 相反，随着湖平面的上升，它最初会连接到一个分布式的基底排水系统，导致缓慢，稳定的泄漏。 湖平面最终上升到足以与远离冰川边缘的树木河道网络建立水力连接。 该方案有四个主要的野外工作目标：1）测量冰坝在湖泊充水和泄水过程中的变形，并描述冰坝的力学行为; 2）测量湖平面随时间的变化，确定湖的高度，测量湖的热结构。3)利用钻孔检查冰坝的水力完整性和冰下排水系统的时间变化; 4）监测冰川终点附近出口河流的洪水和河道形态变化。

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.