ASSESSING MASS BALANCE CHANGE AT SOUTH CASCADE GLACIER: IS IT REPRESENTATIVE OF REGIONAL GLACIERS?

Located in the North Cascade Range in Washington State, South Cascade Glacier provides one of the longest continuous records of annual and seasonal mass balance in the world. This 60-year record chronicles alpine glacier mass change in a mid-latitude maritime climate. The USGS Benchmark Glacier Program, started in 1957 at South Cascade Glacier, 1967 on Wolverine and Gulkana Glaciers in Alaska, and 2005 at Sperry Glacier in Montana, was initiated under the theory that these glaciers are representative within their respective climate regimes. Two recent efforts by the USGS have been undertaken to investigate this hypothesis. First, we developed a generalized algorithm to calculate glacier-wide mass balance consistently across all four glaciers. This process includes a geodetic calibration to correct systematic bias inherent to field methods. We will provide an update on the South Cascade record, newly processed using this algorithm. Second, we are differencing digital elevation models derived from WorldView satellite imagery with the National Elevation Dataset (NED) to quantify mass change for the 1,200 active glaciers in the coterminous United States. The NED source date varies spatially, enabling glacier mass change to be quantified over a 30 to 60-year interval. This dataset will permit statistical evaluation of whether the mass change observed at South Cascade glacier differs from other mid-latitude mountain glaciers in maritime climates.

Since 1958, South Cascade lost approximately 34 m of water equivalent thickness averaged over its surface. Surface lowering and mass loss has occurred over the glacier’s entire elevation range. Preliminary results indicate that South Cascade glacier is losing mass at approximately two to three times the rate as other glaciers in the North Cascade Range. This agrees well with previous efforts by Fountain et al. (2009). This work contributes to our current research investigating the regional patterns of glacier mass loss throughout the coterminous United States.