Englacial and Subglacial Hydrology: A Qualitative Review^*

* Publication number 1120 of the Winchell School of Earth Sciences, Department of Geology and Geophysics, University of Minnesota, Minneapolis.

Abstract

Modern interest in water flow through glaciers can be dated from a pair of theoretical papers published in 1972. In one of these, Shreve (1972) discussed the influence of ice pressure on the direction of water flow through and under glaciers, and in the other Röthlisberger (1972) presented a theoretical model for calculating water pressures in subglacial conduits. Through a combination of these theoretical considerations and field observations, it is concluded that the englacial drainage system probably consists of an arborescent network of passages. The millimeter-sized finger-tip tributaries of this network join downward into ever larger conduits. Locally moulins provide large direct connections between the glacier surface and the bed.

Beneath a valley glacier the subglacial drainage is likely to be in a tortuous system of linked cavities transected by a few relatively large and comparatively straight conduits. The average flow direction in the combined system is controlled by a combination of ice-overburden pressure and bed topography, and in general is not normal to contours of equal elevation on the bed. Although theoretical studies usually assume that subglacial conduits are semicircular in cross section, there are reasons for believing that this ideal is rarely realized in nature. Broad low conduits may be the rule.

When a glacier is moving over a bed of unconsolidated sediment, some water may drain through the sediment. In addition, when high water pressures weaken the sediment, it may be squeezed into subglacial channels, blocking them.