INFLUENCE OF A 100-YEAR FLOOD EVENT ON MELTWATER RESERVOIRS OF THE MATANUSKA GLACIER, ALASKA

In a temperate glacier there are typically one to several meltwater reservoirs affecting the shape and timing of the glacier’s meltwater hydrograph. This study applies recessional analysis to define the number of meltwater reservoirs at the Matanuska Glacier, a large valley glacier (379km²) in south-central Alaska with a relatively long discharge record (1995-2002). Three meltwater reservoirs were identified with mean residence times (K) of 21.0, 37.1 and 88.8 hours. Annual mean K values show a significant drop to their lowest values in 1996, followed by a general increase from 1996 to 1998. During the interval 1999 to 2002, annual mean K values appear relatively stable and show little variation, with values near to those recorded in 1995. A possible explanation for the abrupt decline in K values in 1996 is the occurrence of a 100-year flood event late in the 1995 melt season that radically enhanced the efficiency of the glacier’s drainage network. The gradual recovery of K values following the flood event suggests that catastrophic hydrologic events may have long-term effects (1-3 years) on the efficiency of a glacier’s drainage system. Daily variations in K values were observed within individual melt seasons and an apparent inverse relationship exists between K values and discharge. This relationship demonstrates that short-term variations in meltwater supply can also temporarily alter the efficiency of the glacier’s drainage network.