Water pressure in intra-and subglacial channels*

TLDR: In this article, the authors used the equilibrium equation that at every cross-section as much ice is melted as flows in to show that water must flow in the main arteries of a glacier.

Abstract: Water flowing in tubular channels inside a glacier produces frictional heat, which causes melting of the ice walls. However the channels also have a tendency to close under the overburden pressure. Using the equilibrium equation that at every cross-section as much ice is melted as flows in, differential equations are given for steady flow in horizontal, inclined and vertical channels at variable depth and for variable dischar ge, ice properties and channel roughness. It is shown that the pressure decreases with increasing dischar ge, which proves that water must flow in main arteries. The same argument is used to show that certain glacier lakes above long flat valley glaciers must form in times of low discharge and empty when the dischar ge is high, i.e. when the water head in the subglacial drai nage system drops below the lake level. Under the con ditio ns of the model an ice mass of unif orm thic kness does not float, i. e. there is no water layer at the bottom, when the bed is inclined in the down -hill direction, but it can float on a horizontal bed if the exponent 11 of the law for the ice creep is small. It is further shown that basal streams (bottom conduits) and lateral streams at the hydraulic grade line (gradient conduits) can coexist. Time -dependent flow, local topography, ice motion, and sediment load are not accounted for in the theory, alth ough they may strongly infl uence the actual course of the water. Computations have been carried out for the Gornergletscher where the bed topography is known and where some data are available on subglaeial water pressure. RESUME. Pression de l'eau dans les cond1lites intra- et sous-glaciaires. La cond ition suivante est admise: le