Glacial rebound and the deformation of the shorelines of proglacial lakes

Abstract

A simple isostatic model explaining the pattern of deformation of the shorelines of proglacial lakes has been developed. The rate of glacial retreat before the formation of the shoreline can be derived from the curvature of its uplifted portion. The rate calculated in this way for the retreat preceding the formation of Lake Algonquin is 120 km/103 yr, a value not in conflict with the radiocarbon chronology for this interval. The agreement between the uplift predicted at the iceward extreme of the shoreline (260 meters) and the actual maximum uplift (250±50 meters) provides an independent check on the validity of the model. If the model proves to be correct, the implications are as follows. (1) The continental ice sheets had shapes and total thicknesses during their retreat phases not dissimilar to those observed for present-day ice masses on Greenland and Antarctica, i.e., dynamic equilibrium was maintained; (2) rebound at the edge of large continental ice sheets is a simple isostatic process occurring with the Washburn-Stuiver time constant of about 700 years; and (3) the strength of the crust is sufficiently small to prevent the lateral influence of a continental ice sheet from extending more than a few tens of kilometers beyond its margins.