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.
