Knowledge Bank

Basal ice between -17°C and -18°C is not free to slide on the boulder pavement on which the glacier rests. A debris-rich zone up to 0.6 m thick exists in the lowest part of the glacier. In addition, salts have diffused up to about 6 m above the base. Together these impurities have caused accelerated creep in the basal ice. Rocks, gripped in the deforming ice and rotating in response to the stress conditions in the ice, impinge on the tops of boulders fixed in the substratum, and produce "smears" of powdered minerals, mainly quartz and feldspar. These "smears" parallel the existing ice-flow direction. Cavities exist on the down-glacier side of the larger basal boulders and on some englacial pebbles. Vertical profiles of flow rate parallel to the bed of average slope 120 indicate that the exponent in the simple shear flow law ξ = (σxz/B)n may be as high as 5 or 6. Assuming approximate simple shear near the base of the glacier the diffusion coefficients of Na+ and Ca++ are of the order 107 cm2 s-1 (but could be an order of magnitude less depending on the interpretation of the data) assuming the time of diffusion is 1(±0.5) x 10^4 years.