Elevation Changes on Malaspina, Agassiz and Marvine Glaciers, Alaska, from the Shuttle Radar Topography Mission

The Chugach-St. Elias Mountains bordering the Gulf of Alaska is the location of the largest connected glacier and icefield complex in continental North America: The Bering and Malaspina glacier systems (Molnia, 1993; Sharp, 1951). The Malaspina Glacier piedmont lobe has an area of about 2200 km². Agassiz and Marvine Glacier, on the west-east sides of the Malaspina piedmont, have areas of about 591 and 223 km² respectively. The combined Malaspina-Seward system, including tributaries, has an area of about 4,300 km². Malaspina has a quasi-periodic surge period of 20 to 30 years. The Shuttle Radar Topography Mission/X-Synthetic Aperture Radar (SRTM/X-SAR), flown on STS-99 (February 2000) was the first spaceborne single-pass interferometric SAR mission (Geudtner and others, 2002). The SRTM/X-SAR system was composed of C and X-band SAR. The single-pass SAR interferometer configuration with an inboard (transmit and receive) and outboard (receive only) antenna system enabled the removal of large error sources inherent with the repeat-pass technique. X-band digital elevation models (DEM) produced by the German Remote Sensing Center (DFD) have a nominal pixel size of 25 m-by-25 m in UTM projection. The vertical and horizontal reference datum is World Geodetic System 84 (WGS 84). Nominal vertical accuracy is 6 m (16 m absolute) and horizontal accuracy is 15 m (20 m absolute) at the 90% confidence level. We present new surface elevation changes on the Malaspina piedmont lobe, Agassiz and Marvine Glaciers from 1972-'73 to 2000 based on spatial analysis of co-located Shuttle Radar Topography Mission X-band DEM with United States Geological Survey DEMs. X-band DEM elevations were changed from the WGS 84 vertical datum (ellipsoid) to the GEOID 99-Alaska (NOAA National Geodetic Survey geoid) datum. USGS DEMs were transformed from North America Datum 1927 (NAD 27) to WGS 84 in UTM projection. A correction for X-band radar penetration depth of snow cover is in progress. Preliminary results indicate the Malaspina piedmont surface lowered on average by 43 +/- 4 m from 1972 to 2000 (1.6 +/- 0.1 m a^-1) for a volume loss of 59 +/- 5 km³ in water equivalent (we). The spatial distribution of surface lowering is non-uniform for all three glaciers. The Marvine Glacier shows an average of 50 +/- 4 m we of surface lowering. The Agassiz Glacier shows an average of 24 +/- 4 m we of surface lowering. However, Agassiz Glacier has a bulge of surface rising up to 52 +/- 4 m, about 4 km in diameter, located across from Agassiz Lakes.

Geudtner and 3 others, Interferometric alignment of the X-SAR antenna system on the Space Shuttle Radar Topography Mission, IEEE Trans. on Geoscience RS, 40 (5), 995-1005, 2002.

Molnia, Major surge of the Bering Glacier, Eos, 74 (29), 321-322, 1993.

Sharp, Accumulation and ablation on the Seward-Malaspina glacier system, Canada-Alaska, Bull. Geo. Soc. Am., 62, 725-744, 1951.