A THEORY OF SUBGLACIAL GROUNDWATER STRUCTURE AND FLOW IN AREAS OF MODERN AND ANCIENT GLACIATION

Glacier drilling and pressure measurements reveal that groundwater flow is an important means whereby basal meltwater and surface water penetrating to the bed of a glacier are scavenged by longitudinal subglacial streams before being discharged from beneath the glacier. This creates a distinctive structure to the groundwater system, analogous in form to that of the water table in hilly, temperature, non-glaciated regions, with the groundwater head determined by glacier and hydrogeologic characteristics, which evolves rapidly as the glacier advances and retreats, in contrast to relatively stable patterns of head forcing in non-glacial terrains. Modelling suggests how the evolving groundwater system determines the pressure distribution at the glacier/bed interface, which helps determine glacier dynamic behaviour, and is a source of coupling between the glacier and groundwater systems. The model is tested by pressure and geochemical measurements beneath modern glaciers and the geochemistry of carbonate precipitates in areas of Pleistocene glaciation, where it also explains anomalous patterns of groundwater distribution.