Glaciohydraulic supercooling is an active process on many modern glaciers in Alaska, such as the Bering, Malaspina and Matanuska Glaciers, and in Iceland, most notably, Skeidjarárjökull. These glaciers have an abundant supply of melt water at the glacier's bed, geophysical evidence and ice surface features that indicate the glacier ice is flowing through an overdeepened basin and the slope of the ice surface is low and opposite to that of the basin. Where turbulent water flows up a slope >1.2 to 1.7 times the downward ice surface slope glaciohydraulic supercooling and ice accretion is predicted (Alley and others, 1998). Glaciohydraulic supercooling is hypothesized to cause basal freeze-on, whereby the supercooled water flashes to frazil ice and the ice acts as a sieve as dirty subglacial water filters through it. Such processes may be significant to the geologic record by allowing glaciers to entrain large volumes of sediment that can be transported long distances (Lawson and others, 1998). Given the large moraine complexes deposited by the lobes of the Laurentide ice sheet and their association with overdeepened basins such as the Great Lakes and the Finger Lakes, it is not unreasonable to suspect that glaciohydraulic supercooling and basal freeze-on processes operated on the ice sheet. This hypothesis is tested on the Superior lobe of the Laurentide ice sheet using geographic information systems. Model inputs include a digital elevation model, the bathymetry of Lake Superior and a constructed model of ice surface topography during the St. Croix phase, when the conditions necessary for basal freeze-on were most likely to have occurred. GIS is used to calculate the slope of the glacier's bed as well as its ice surface. Where the bed slope is opposite to the ice surface slope and their ratio is between 1.7 and 11, glaciohydraulic supercooling and basal freeze-on are hypothesized to have operated on the Superior lobe of the Laurentide ice sheet.
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