Paper No. 1
Presentation Time: 8:00 AM
GPR STUDIES ALONG THE PRESENT AND PAST COASTLINES OF THE GREAT LAKES
JOL, Harry M., Department of Geography and Anthropology, Univ of Wisconsin- Eau Claire, 105 Garfield Ave, Eau Claire, WI 54703-4004, FISHER, Timothy G., Department of Earth, Ecological and Environmental Sciences, Univ of Toledo, MS #604, 3801 Bancroft Street, Toledo, OH 43606-3390, LOOPE, Walter L., U.S. Geol Survey, N8391 Sand Point Road, P.O. Box 40, Munising, MI 49862, SMITH, Derald G., Department of Geography/Earth Sciences Program, Univ of Calgary, 2500 University Drive, Calgary, AB T2N 1N4 and MOORE, Laura J., Geology Department, Oberlin College, 52 West Lorain Street, Oberlin, OR 44074, jolhm@uwec.edu
Many projects investigating coastal depositional features commonly base their results on morphology, drill core, available outcrops, or models. Ground penetrating radar (GPR) studies conducted within large lake basins across North America have provided detailed subsurface stratigraphic information. The Great Lakes contains one of the greatest concentrations of coastal depositional features in the world. This paper presents a summary of results from GPR studies conducted along recent and past coastlines of the Great Lakes including 1) Lake Superior (barrier, spits, tombolos, Lake Nippissing shorelines, gravel beaches), 2) Lake Michigan (sand beaches, aeolian), 3) Lake Erie (spits, barriers, beaches), 4) Lake Ontario (barriers, spits, beaches).
GPR is an electromagnetic geophysical tool that enables one to image (2D & 3D) the subsurface stratigraphy of coastal environments in a continuous, non-destructive, and non-invasive manner. The GPR acquisition systems used for the study were pulseEKKO 100 & 1000 with antennae frequencies ranging from 50 MHz to 450 MHz and transmitter voltages ranging from 200 volt to 1000 volt. Step sizes and antennae separation varied depending on antennae frequency chosen and on the site conditions. The digital profiles were processed and plotted using pulseEKKO software. Depths of deposits were calculated using near surface velocity measurements from collected common midpoints.
Radar stratigraphic analysis on the collected data provided the framework to investigate both lateral and vertical geometry and stratigraphy of the coastal deposits. GPR profiles, with depths of penetration greater than 30 m, reveal patterns showing coastal growth by aggradation and/or progradation as well as features showing coastal erosion . Interpretations of the results suggest that several different coastal processes are at work within the Great Lakes including longshore transport, changes in sediment supply, and response to lake level changes.
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