Collaborative Research: Outbursts from an Ice-Dammed Lake

这是一项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在内的合作研究。当冰坝的水体突然排水时，就会发生突发洪水。这些洪水会对下游造成毁灭性的影响。它们可以极大地重塑河道，并可能对人类住区构成威胁。由于溃决洪水是不可预测的，其储水和释放的机制（时间、规模和地貌效应）研究较少。我们所知道的主要来自冰岛的观测，那里的冰下湖和冰边缘湖周期性地排水。在其他地方，观察是偶然的或事后的。首席调查员将调查弗兰格尔圣的肯尼科特冰川上一个可预测的、每年爆发的地点。埃利亚斯国家公园，阿拉斯加。冰封边缘的隐溪湖的排水危及附近的居民和国家公园的游客。主要研究人员将检查爆发洪水触发，开始测试和完善现有的理论模型。他们的假设是，冰坝不会形成一个“紧密的”水力密封，不会被浮力突然打破。相反，随着水位的上升，它最初与一个分布式的基底排水系统相连，导致缓慢而稳定的泄漏。最终，湖水水位上升到一定程度，与远离冰川边缘的乔木河道网络建立了水力连接。然后，湖泊迅速排水，这可能与管道系统的季节性发展或冰川涌流的终止状态有关。野外工作有四个主要组成部分：1)测量冰坝在湖泊填满和排空时的变形，并描述冰坝的力学行为；2)测量湖泊水位随时间的变化，确定湖泊温度，测量湖泊热结构。这些数据将构成约束溃决洪水模型的基本边界条件；3)利用钻孔研究冰坝的水力完整性和冰下排水系统的时间变化；4)监测冰川末端附近出水口的洪水和河道形态变化。他们将使用探地雷达对河床进行调查，这将迅速给出详细的横截面，并将用于校准流量，并记录洪水期间河道的变化。该研究有助于加深对溃决洪水的认识，改进预测方法。研究结果将提供对冰川过程的深入了解，如季节性排水系统演变、潮涌终止以及基础水文和冰川动力学之间的联系。

This 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.There are four main components 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. These data will constitute fundamental boundary conditions to constrain models of the outburst floods; 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. They will use ground penetrating radar to survey the stream bed which will rapidly give detailed cross sections and will be used to calibrate discharge and to document channel changes during the flood. This study should provide a better understanding of outburst floods and improve prediction methods. The results will provide insight into glaciological processes such as seasonal drainage system evolution, surge termination, and the link between basal hydrology and glacier dynamics.