IMPROVING GLACIAL GEOLOGY MAPS AND INTERPRETATIONS THROUGH GEOPHYSICS

Geologic maps of glacial features across North America have benefited immensely from the application of geophysical methods to generate three dimensional images of the landforms. Recent investigations in Michigan and New York illustrate several improvements to geologic interpretations made possible through the use of Ground Penetrating Radar (GPR) and Electrical Resistivity Tomography (ERT).

The last glacial maximum occurred 26,000 years bp, covering several of the northern States completely. Advance and retreat of glaciers across the northern reaches of the continent developed the landscape that is seen in this region today. The dynamic hydrology of glacial environments built outwash plains and meltwater channels and developed immense beds of lacustrine deposits and glacial tills. Sediments and erosion surfaces left by the glaciers provide clues to the sequence of glacial history, but those sediments and structures can be difficult to access as glacial deposits may be greater than 100m in thickness. Interpretations limited to surface exposures and borehole data often fail to identify details and heterogeneity within thick sequences of glacial deposits, leading to misinterpretation of glacial history and thus misconceptions of the geologic environment in place today. This can be important not only for understanding the history of the region, but also for hazard assessment and hydrogeology applications.

GPR and ERT surveys of glacial landscapes can be used to identify heterogeneities and structural details at depth. These non-intrusive techniques are used to investigate the upper 30m of the subsurface in Michigan and New York for a wide range of glaciology problems, from ancient Great Lakes water levels to hazard assessment at the largest landslide in New York State history. Interpretations of the geophysical data are made in conjunction with standard techniques such as surface mapping and borehole logging as well as with the novel technique of optically stimulated luminescence (OSL). The results of these investigations demonstrate the importance of geophysical methods in improving geologic maps and interpretations in glacial environments.