Permeability, Brine Content and Temperature of Temperate Ice

Abstract

A temperate glacier is defined as a glacier containing liquid inclusions in which the concentration of salts is not too high. Nevertheless these salts suffice to produce a depression in temperature comparable with that due 10 the pressure, and much greater than that due to interfacial energies. Because of this a large part of the liquid water present in the ice is not mobile, contrary to the theory of Nye and Frank. Deformation and recrystallization is bound to close off capillary intergranular channels, for glacier ice is usually impermeable. An explanation is given of why firn, at a depth which the annual cold wave does not reach, is nevertheless transformed relatively suddenly into practically impermeable ice. Saline inclusions will migrate with a velocity inversely proportional to the potential temperature (difference from the melting point of pure ice at the pressure in question) and proportional to the gradient of this potential temperature. This velocity, the salinity, the liquid water content, and the ice temperature, parameters which are all functions of the depth, are calculated for a steady state in a stagnant or moving glacier. Under the action of anisotropic stresses, isolated inclusions perpendicular to the maximum compressive stress will enlarge at the expense of their neighbours. If however the two inclusions are connected by a capillary channel, no enlargement occurs, but instead the salt content decreases, evacuated to the other inclusion. This process would constitute an objection to the theory of glacier sliding by melting and refreezing around small obstacles, unless new subglacial mechanisms were to occur.