SUBGLACIAL HYDROLOGY OF THE JAMES LOBE OF THE LAURENTIDE ICE SHEET

Subglacial hydrology played an important role in the dynamics of the Laurentide Ice Sheet through its potential contribution to subglacial sediment deformation and sliding. The advance of the ice sheet also affected and possibly reversed regional groundwater flow. To determine these effects and feedbacks, we modeled the subglacial hydrology of the James Lobe of the Laurentide Ice Sheet over a region from Hudson Bay to the Missouri River covering the eastern half of the Williston Basin and part of the western Canadian Shield. Simulations suggest that because of the limited penetration of meltwater through the upper-Cretaceous shale, the James Lobe had little effect on regional groundwater flow, reversing flow only in the surficial Quaternary sediment and upper-Cretaceous shale. This suggests that northward groundwater flow out of the Williston Basin has likely persisted at least through out the Quaternary. Simulations also suggest that subglacial aquifers were incapable of draining the ice sheet bed and that drainage therefore must have depended on the establishment of a subglacial drainage network at the ice-bed interface, which presumable maintained basal water pressure near the ice-overburden pressure. We simulated a canal-type drainage system at the ice-till interface with conduit geometry based on a theoretical karst aquifer analogue. Results suggest that the ice sheet bed could drain and remain coupled to its bed with subglacial canals up to 70 cm wide and spaced on the order of 50 to 120 meters consistent with the drainage system suggested for the Whillans Ice Stream of the West Antarctic Ice Sheet.