Dynamic controls on Eklutna Glacier Mass Loss - Louis Sass , Alaska Pacific University (co-authors: Michael G Loso/Alaska Pacific University, Shad 0’Neel/Alaska Science Center - USGS, Joseph A MacGregor/ University of Texas Institute for Geophysics - Austin, TX, Ginny A Catania/University of Texas Institute for Geophysics - Austin, TX, Chris F Larsen/ University of Alaska, Geophysical Institute, Fairbanks, AK)

ABSTRACT

We investigate the role of ice dynamics in observed mass loss at Eklutna Glacier, a small alpine glacier in the western Chugach Mountains, Alaska. Meltwater from Eklutna Glacier is the primary input to Eklutna Reservoir, which supplies >80% of the drinking water and >10% of the power used by Anchorage, Alaska’s largest city. Net mass loss from Eklutna Glacier is responsible for approximately 10% of the total inflow to Eklutna Reservoir since the 1950’s. Airborne laser profiling by University of Alaska Fairbanks shows that the glacier has thinned by an average of 42 m since it was mapped in 1957 and, contrary to a typical response to climate, much of the volume loss occurred in a broad basin near the top of the glacier. This work examines the relative importance of changes in mass-balance distribution and changes in ice dynamics to resolve the cause of rapid mass loss on the upper glacier. Our efforts include supplementing an ongoing mass-balance monitoring program with ice thickness and motion measurements. We used 5-MHz radar to resolve a maximum ice thickness of 430m located in the upper basin, with a prominent bedrock sill separating this basin from the lower glacier. Summer surface velocities, measured with GPS, vary from 7 to 20 cm/day and generally increase down glacier. Taken together, these data help constrain the relative importance of surface mass-balance and dynamics in recent mass loss. Dynamic thinning in the upper basin is caused by a reduction in ice flux entering the upper basin, but the rate of thinning is regulated by the dynamics of ice flux exiting the basin across the sill. A feedback loop between surface deflation and negative mass balance is underway and will likely continue until the glacier terminus retreats above the sill. Even in the absence of additional warming this feedback loop will promote a continued negative mass-balance trend at Eklutna Glacier. Because the sill limits the rate of thinning in the upper basin the negative mass-balance trend is likely to persist over decadal and longer time scales.

Topic: Climate Change