BED MORPHOLOGY OF BERING GLACIER, ALASKA

Alaska’s Bering Glacier is the largest and longest glacier in continental North America. Previously, we used GIS to analyze and integrate USGS reflection and refraction seismic data, ice-surface ice-penetrating radar (IPR) data, and NASA Warm Ice Sounding Explorer (WISE) airborne radar data to map the depths and morphology of the complex subglacial fiord system that underlies a 75-km-long segment of Bering’s eastern piedmont lobe. The data synthesis revealed that a complex subglacial fiord system, in places as much as 380 m below sea level, reaches more than 65 km up-glacier from Bering’s Little Ice Age end moraine complex. The WISE radar data that were used were collected in 2008. WISE, a 2.5 MHz radar that measures the nadir thickness of warm, fractured glacier ice, is based on the MARSIS planetary sounder. The WISE data both confirmed and expanded our initial interpretation of the fiord system’s characteristics that was largely based on IPR data collected more than 15 years earlier.

This investigation used additional 2008 WISE data and a new 2012 WISE dataset to extend the mapping of Bering Glacier’s bed to include the entire eastern part of the glacier. This additional ~100 km length of the glacier extends from the Bering Glacier/Malaspina Glacier divide in Canada to the western end of the Bagley Ice Valley. In all, ~718 km of radar profile lines were produced and analyzed. About 138 km of profiles were along the centerline of the glacier, while the remaining ~580 km were located in 60 cross profiles, perpendicular or oblique to the centerline. Data holidays account for ~14% of total profile line lengths.

Generally, centerline bed elevations in easternmost Bering Glacier are in the ~1,300-1,600 m above sea level (asl) range. At the western end of the Bagley Ice Valley, centerline bed elevations are in the ~100-300 m asl range. One area, ~95 km up glacier, has a bed elevation of <100 m asl. Ten kilometers to the east, the bed rises to ~600 m asl, and it remains close to that elevation for ~15 km. It continues to rise to Bering Glacier’s origin with only a few 100 m of variability. Bed complexity in the Bagley Ice Valley area is low compared to the piedmont lobe area where several deeply eroded channels create 300-400 m of local relief. Centerline ice thicknesses observed range from <200 m near the terminus to >1.1 km in the western Bagley Ice Valley.