Date of Award

2010

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Earth Sciences

Advisor

Karl Kreutz

Second Committee Member

Steven Arcone

Third Committee Member

Peter Koons

Abstract

Mountain and alpine valley glaciers are often described by their thermal characteristics, which, in turn, are heavily influenced by environmental factors such as latitude and elevation, amongst others. Low elevation and/or low latitude glaciers that experience melting throughout the snow pack are in the wet zone. Whereas glaciers at higher elevations and/or higher latitudes that experience some melting and refreezing, or no melting, are in the percolation and dry zones, respectively. Defining boundary elevations between these melt regimes is a fundamental step to determine where melting occurs, both locally (glacier scale) and regionally (mountain range scale). Secondly, ice cores, a primary source of paleoclimate information, require glacier ice which has experienced minimal melting and deformation. Herein, I use ground penetrating radar (GPR), geodetic, and glaciochemical evidence collected on three glaciers from the Alaska Range, to estimate regional melt regime boundary elevations. I simultaneously use the same evidence to assess englacial stratigraphy and flow dynamics of the three glaciers and make recommendations for potential ice core drill sites based on pre-determined drilling criteria. Glaciochemical and snow pit stratigraphy collected at Kahiltna Pass Basin on Mount McKinley (3100 masl) show evidence of some melt and refreezing in the snow pack and firn suggesting this site is in the upper region of the percolation zone. Radar profiles and surface velocity data show a maximum depth of 300 meters in the basin and westward dipping englacial stratigraphy that experienced vertical thickening as it flowed from a steep, narrow, and high velocity valley into a flat, wide basin in which velocities were slower. Stratigraphy on the western side of this basin is surface conformable, but likely experiences some fanning and thinning due to the increasing basin dimensions relative to the narrow valley, up-glacier. Radar profiles show that isochronal integrity is preserved and mostly continuous within the upper -150 meters despite the compression and expansion events. However, signs of entrained avalanche debris and significantly deformed ice are present near the steeply dipping layers and at depths greater than 150 meters. I find that continuous stratigraphy appropriate for ice core studies exists to -150 meters on the western side of the glacier; however buried avalanche debris and deformation caused by up glacier events may limit the usefulness of core from deeper depths. Using flow models, I calculated a maximum depth-age relationship between 77 and 83 years at -150 meters depth and 684 years at 300 meters depth. Radar profiles from Mount Russell (2770 masl) show a significant melt signal at the firn ice transition (-50 m depth) suggesting this elevation is in the upper reaches of the wet zone and an inappropriate ice core site. An ice divide on Mount Hunter (3907 masl) shows surface conformable strata and -270 meters of ice. Minimal signs of melt or deformation suggest the divide is in the dry zone and an appropriate location to drill a multi-century core.

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