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A numerical model of a spherical viscoelastic self-gravitating Earth has been used to predict the glacio-isostatic deformation of the Lake Michigan basin during late-glacial and postglacial times. Predictions of present rate of vertical movement agree well in trend but slightly exceed in magnitude the observed rate of tilting indicated by lake-level gauges. Predicted uplift curves for the four dominant outlets controlling the ancestral lakes of the Lake Michigan basin indicate an outlet chronology comparable to that proposed by glacial geologists despite the fact that the Chicago and Port Huron outlets are not predicted to be stable as is commonly believed. Predictions of tilting of the Algonquin shoreline match observations north of the Algonquin hinge line, but the predicted shoreline plunges below the present level of Lake Michigan at the hinge line location. In opposition to the commonly held belief in crustal stability south of the Algonquin hinge line, the predictions indicate considerable vertical movement there continuing to the present. If the predictions are correct, the subhorizontal shorelines south of the hinge line have been misinterpreted because the Glenwood shoreline, reported to be subhorizontal there, is predicted to be strongly tilted. Alternatively, correct interpretation of this shoreline implies serious deficiencies in the assumed ice-sheet history or Earth rheology used as input to the model.

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