Internal melting and ice accretion at the bottom of temperate glaciers

Abstract

AbstractTemperate glacier ice is neither dry nor impermeable, as the standard theory of glacier sliding assumes. This fact leads to the already published concept of locally stress-controlled temperatures. Why the temperature is determined by the highest principal pressure, why the microscopic stress equals more or less the macroscopic one, and why water may flow in the capillary network even when water lenses at grain boundaries are freezing is explained. The new concept is applied to ice sliding on a hard bed having a sine profile, without cavitation. First, the stress field for a Newtonian viscous material and a vanishing roughness are used; next, an improved one, that takes into account the non-linear viscosity of ice and the finite amplitude of the micro-relief. It appears that water migrates from the stoss sides of the bumps to the lee sides within a bottom layer of thickness hw. Moreover, there is less ice melting at the sole on the former ones than ice accretion on the latter, a fact that yields a trend of ice accretion at the glacier sole. It is balanced by internal melting near the bed and water oozing at the interface from the soaked ice. Consequently, a thin layer of accreted regelation ice with a constant mean thickness hi should exist at the interface. Modelling realistically mountain glaciers, hw ∼ 20 cm and hi ∼ 3.5 cm are found.