Outbursts From an Ice-Dammed Lake: A Collaborative Study

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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.