2005 Salt Lake City Annual Meeting (October 16–19, 2005)

Paper No. 3
Presentation Time: 1:30 PM-5:30 PM


JACKSON, Keith M. and FOUNTAIN, Andrew G., Geography, Portland State University, Dept. of Geography, Portland State University, Portland, OR 97207, kjack@pdx.edu

Much of the research concerning alpine glaciers has focused on “clean” glaciers largely devoid of rock material. However, debris-covered glaciers are common and can be found on stratovolcanoes of the western U.S., the Hindu Kush-Himalaya region, the Andes, and elsewhere. Consequently, little is known about the mass balance processes and effects of climate change on debris-covered glaciers. Eliot Glacier is a small (1.6 km2) glacier on Mt. Hood, Oregon. Although it has been retreating as a result of climate warming, the sensitivity of its response is unclear because the ablation zone is largely covered by rock debris. We examine three interrelated processes on this glacier, the spatial pattern of ablation, flow speed, and the rate of debris supply to the glacier surface. Initial work on Eliot Glacier dates to the 1920s when the Mazamas (hiking club) started a measurement program. Two cross-sectional elevation profiles were repeatedly surveyed from 1940 to 1982. Since the 1920s, the glacier has thinned and retreated in response to climate warming. Our resurveys show substantial thinning at the lower profile (now stagnant ice) and little to no thinning at the upper profile, 800 m upglacier. Summer ablation decreases from about 10 cm/day on clean ice from just above the upper profile to < 1 cm/day 500 m downglacier where debris is about 1 m thick. Surface supply of debris decreases with thickening debris cover (inverse relationship with ablation). Surface velocities near the upper profile have decreased from an annual average of 7 m/yr in the 1960s to about 5 m/yr in the late 1980s to the current average of 4.5 m/yr.