The Great Lakes region has experienced significant and dramatic changes in hydrologic character since late glacial times, 17,000 years ago. Large proglacial lakes drained suddenly and the slow viscous deformation of the earth caused outlets to move vertically affecting the associated lake levels. The proposed research will use a numerical model of viscous flow within the mantle to simulate deformation of the earth's solid surface relative to its geoid that was caused by the changing ice loads during the last ice age. Shorelines of the ancient glacial and postglacial lakes are now tilted relative to the present geoid and provide data of time-dependent earth deformation. An inverse model will also be used to predict the thickness of the ice sheets consistent with the deformation data. The main goal of the research is to simulate the changing hydrologic nature of the entire Great Lakes region during the past 17,000 years. Because digital elevation models (DEM's) exist over the entire region, predictions of deformation everywhere in the region allow calculation of paleo-topography. It is common to use geographic information systems (GIS) to determine modern stream networks given present topography (DEM's). In the proposed work, a GIS will use the predicted paleo-topography to determine the integrated river systems and lake levels that were continually modified as retreating ice exposed progressively lower outlets and as outlet elevation change resulted from isostatic uplift. Calculations are readily performed in the GIS of exact volumes of freshwater released by lakes as glacial burst events. Such estimates are important because cold freshwater pulses, affecting ocean circulation patterns, may have contributed to extremely rapid climate change. The GIS can also determine paleo- drainage basins and stream networks with quantification of the total area contributing surface water to any point on any stream and at any time. Predictions of shorelines will be superimposed upon USGS digital raster graphics topographic maps for use in field checking the predictions, and these predictions will be available to all on a website or CDs. The predictions can also be downloaded onto a handheld computer connected to a global positioning system (GPS) device and used to pinpoint in the field exact locations of shoreline features, whether predicted or observed. The inverse model will tune the ice sheet history and earth rheology to the data. Successful inversion will yield a predicted ice sheet thickness history helpful to glaciologists and glacial geologists attempting to understand the dynamic nature of the southern limit of the Laurentide ice sheet. It will also serve to address the issue of crustal stability in the southern Great Lakes and improve the understanding of earth viscosity structure and neotectonics of the region. The research will expose undergraduate geology majors to numerical models, statistical methods, advanced GIS practices and fieldwork. Their continued active participation in Geological Society of America sectional meetings and as co-authors on publications will stimulate the research environment of a small undergraduate geology department and encourage undergraduates to continue their education as researchers in graduate school and beyond.
