IMPACT OF THE 1993-95 SURGE ON THE MORPHOLOGY OF ICE-CONTACT TSIU LAKE, BERING GLACIER, ALASKA

Unlike most Alaska glaciers, the Bering piedmont lobe terminates on a foreland of islands separating a series of ice-contact lakes, including Tsiu Lake. The Bering is known for cyclic surges that have had significant impact on foreland terrain. The purpose of this investigation is to assess the erosional and depositional impact of the 1993-95 surge and retreat on the pre-surge Tsiu Lake basin depth and morphology.

Consistent with field studies during the past two decades, a 2008 bathymetric survey of Tsiu Lake basin was conducted using Lawrance sonar that recorded GPS locations for hundreds of depth measurements on this 3 km2 lake. Data were initially processed in the field using a GIS format, thus yielding real-time maps and 3-D models depicting lake basin morphology followed by a Surfer and ARC applications in the laboratory. These data combined with bathymetric data from previous years yields an average rate of sedimentation of 3 m/yr (2005-2008). Combined with rates determined for the interval between 1991 and 2008 (including the surge, subsequent retreat, and post-surge delta growth into the lake) we have determined that ice entering the lake basin during the surge resulted in lake bottom erosion of 3m.

Unique to this investigation is a knowledge of foreland terrain prior to, during, and after the 1993-95 surge, coupled with changes in lake level due to breakout events during a decade of retreat from the surge limit. This investigation provides insight to processes and rates of change that would otherwise go undetected.