Sub-permafrost water storage beneath subpolar ice sheets

Abstract

Sub-permafrost water storage is shown to occur beneath both the toe and the near proglacial region of subpolar ice sheets. Depending upon the distribution of the overburden in the proglacial region, a substrate water pocket may form which extends hundreds of meters to kilometres in the direction of glacier flow. The rate of water storage increases with increasing storativity of any underlying aquifer. If, in addition, there is a soft aquitard of low permeability located above the aquifer the aquitard can become fluidized by the upwelling of groundwater, particularly in the case of a steeply sloping terminus such as a calving terminus. If the terminus is gently sloping the substrate is normally stable to shear deformation. If the proglacial bed dips downglacier (which rules out a proglacial moraine) large water pockets do not form but sub-permafrost ponding will normally occur. The uplift of permafrost by water pockets is thought to be important to glaciotectonic activity.