RETREATING AND THINNING GLACIERS IN DENALI NATIONAL PARK AND PRESERVE

Long-term ecological monitoring in Denali National Park and Preserve includes measuring the mass balance of the park's glaciers as an indicator of climate change. Apart from the systematic detailed yearly measurement of three index glaciers we also attempt to measure the location of the terminuses and centerline elevations of different glaciers each year. Using a Trimble Geo3 GPS centerline elevations were measured for three glaciers, Foraker, Straightaway, and Middle Fork Toklat Glaciers. The elevations measured during the surveys were compared to the elevations on the USGS 1:63,360 topographic maps. The average thinning rate for these three glaciers is –0.55 m/year, which correlates well with the average thinning rate of Alaskan glaciers measured by Arendt et al. (2002) for the time period between the mid-1950s to the mid-1990s, -0.52 m/year. The terminus retreat of five glaciers was measured by comparing the terminus location extent during the mid-1950s, using USGS air photos, to GPS surveys and the newly acquired (2004) IKONOS satellite imagery. The retreat distances range from 0 to 2063 meters, averaging 667.9 meters, corresponding to retreat rates of -0 to -38.93 m/year, averaging -12.60 m/year.