Postglacial Uplift Predictions and Historical Water Levels of the Great Lakes

Abstract

Historical water levels of the Great Lakes have long been employed to estimate the relative vertical motions caused by postglacial uplift, but the question of whether or not there is real subsidence in the southernmost Great Lakes region cannot be answered by the determination of relative motions alone. At present, it is not possible to estimate this motion in an “absolute” frame of reference unless a model of glacial isostatic adjustment is used. The predictions of two such models (one of which was the new ICE-3G model) were directly compared to historical water-level data from Ontario and the United States and to a long-established model based on water-level data. Of the 247 rates of relative motion estimated from pairs of water-level gauges, 130 were matched by the predictions ofICE-3G, 89 by an older glacial isostatic model, and 189 by the model based on water-level data. When only long-duration (≥50 years) records were analyzed, the number of agreements were 20, 13, and 42, respectively, out of 50 pairs. Most of the disagreeing pairs involved gauges located in Lakes Ontario and Michigan. The performance of each model was assessed and its deficiencies discussed.