From our paper in the Journal of Glaciology 46(153): 311-325. (2000)

A Numerical Investigation of Ice-Lobe--Permafrost Interaction Around the Southern Laurentide Ice Sheet

Paul M. Cutler¹, Douglas R. MacAyeal², David M. Mickelson¹, Byron R. Parizek³, Patrick M. Colgan⁴

¹ Department of Geology and Geophysics, University of Wisconsin, U.S.A. ² Department of Geophysical Sciences, University of Chicago, U.S.A. ³ Department of Geosciences, Pennsylvania State University, U.S.A. ⁴ Department of Geology, Northeastern University, Boston, MA, U.S.A.

Permafrost existed around and under marginal parts of the southern Laurentide Ice Sheet during the last glacial maximum. The presence of permafrost was important in determining the extent, form, and dynamics of ice lobes and the landforms they produced because of influences on resistence to basal motion and subglacial hydrology. We develop a two-dimensional time-dependent model of permafrost and glacier-ice dynamics along a flowline to examine: i) the extent to which permafrost survives under an advancing ice lobe and how it influences landform development and hydrology, and ii) the influence of permafrost on ice motion and surface profile. The model is applied to the Green Bay Lobe, which terminated near Madison, Wisconsin during the last glacial maximum. Simulations of ice advance over permafrost indicate that the bed upstream of the ice-sheet margin was frozen for 60 to 200 km at the glacial maximum. Permafrost remained for hundreds to a few thousand years under advancing ice, and penetrated sufficiently deep (tens of meters) into the underlying aquifer that drainage of basal meltwater became inefficient, likely resulting in water storage beneath the glacier. Our results highlight the importance of permafrost on subglacial conditions, even though uncertainties in boundary conditions such as climate exist.