Glaciological investigations, Nunatarssuaq ice ramp, northwestern Greenland
Nobles, Laurence H. (Laurence Hewitt), 1927-
Technical ReportSummary: The margin of the ice cap in northwestern Greenland is formed by a relatively thin ice carapace resting on a very rugged sub-ice topography. The Nunatarssuaq ice ramp is a gently sloping ice mass approximately 4 miles long by 2 miles wide that forms part of this margin 30 miles northeast of Thule. The ice of the Nuna ramp is of subpolar type, in which negative temperatures prevail throughout most of the year in all but the upper few feet. At a depth of 25 ft the ice temperature is constant throughout the year at -14°C; only the upper 2-3 ft of ice is at 0°C by the end of the melt season. Thus the temperature regimen of this high-polar ice is strictly analogous to that of perennially frozen ground. All runoff is on the surface, forming such surface features as slush avalanches, algal pits, and an integrated drainage pattern. Net accumulation as high as 25 in. of water equivalent was measured at Morris Station, 30 miles from the border of the ice cap, but most of the Nuna ramp proper is blown free of snow in winter by strong winds. Ablation of 20 to 25 in. of water during the melt season is common on the lower Nuna ramp. The most severe ablation is on days of moderately high temperature accompanied by moderate winds. The firn limit on the ramp is at about 3000 ft elevation. Comparison between the total amount of ice ablated from the lower ramp and the amount delivered to the ramp by flow through the gap south of Nuna Knob indicates a strongly negative budget balance for the ramp during the period studied. Velocity of ice movement on the Nuna ramp is 1 to 2 in. per day. Level measurements indicate that the angle of the movement vector never differs from the horizontal by more than 5°. Calculations of the amount of movement of ice toward the surface to replace that lost by ablation also indicate a strongly negative budget balance and suggest complete decay of the ramp in 300 to 600 years under present climatic conditions. Deformation of the ice during flow has formed a number of metamorphic structures of both tensional and shear origin. These include foliation, blue bands up to 20 ft thick, amber bands, consisting of unequally distributed, finely divided debris; joints-, small crevasses; and ice dikes. NOTE: This file is very large. Allow your browser several minutes to download the file.
U.S. Army Snow, Ice, and Permafrost Research Establishment.Engineer Research and Development Center (U.S.)
Glaciers; Glacier ice; Glacier mass balance; Glaciology; Ablation; Glacier movement; Ice structure; Ice cover thickness; Greenland
SIPRE report ; 66.
Approved for public release; distribution is unlimited.