Using NASA Warm Ice Sounding Explorer (WISE) Data to Reexamine the Bed Morphology of Malaspina Glacier, Alaska
Abstract:In 1988, a USGS ice-penetrating radar (IPR) survey of eastern Malaspina Glacier was conducted (Molnia and others, 1990) to determine the configuration of the glacier’s bed and to measure ice thickness at more than 50 locations. The IPR survey results suggested that much of the glacier area investigated was underlain by fiord channels that extended as much as 50 km inland from the present Gulf of Alaska coastline. Maximum measured fiord channel bed depths exceeded 200 m below sea level, while the maximum ice thickness measured was more than 850 m. The IPR survey was conducted to test a hypothesis (Molnia and Jones, 1989) that unusual airborne radar backscatter features observed on a November 1986 X-band, high-resolution, synthetic aperture radar (SAR) image of the glacier’s surface were expressions of the glacier’s bed morphology, surface topography, surface wetness, ice structure, and ice flow characteristics. The most significant type of feature seen on the SAR image were several 10-25 km-long by 1.5-2.5-km-wide, north-south trending fiord-like glacial valleys, each with adjacent cirque-like amphitheaters. Field surveys in 1989 showed the valleys were topographic lows, while the cirque-like features were heavily crevassed topographic highs. Closely spaced IPR soundings showed that the ice associated with the valleys is substantially thicker than the ice over the adjacent cirques.
In 2008 and again in 2012, NASA’s airborne Warm Ice Sounding Explorer (WISE) was flown over Malaspina Glacier, producing more than 500 km of new soundings. Not only did this provide an opportunity to better map the glacier’s bed, calculate ice thickness, and determine ice surface elevations, it also provided an opportunity to reexamine the Molnia and Jones hypothesis.
Bed morphology profiles generated from the WISE data were co-registered to and compared with the 1986 X-band radar image. The results show a strong correlation between radar surface low backscatter surface channel features and areas of maximum bed depth.