HIGH FREQUENCY (225, 450, 900 MHZ) GPR INVESTIGATION OF THE NIPPISING BEACH RIDGE, HURON MOUNTAINS, MI

Our research investigates the internal structure of the primary beach ridge within a strand plain located along the Huron Mountain section of the Lake Superior shoreline in Michigan. Beach ridges act as a record of past lakeshore positions, and the analysis of the subsurface stratigraphy can reveal past beach forming processes. The beach ridge represents the peak of lake level rise of Lake Nipissing. Ground penetrating radar (GPR) is a geophysical method used to collect transects that image the subsurface of the beach ridge and allows one to analyze sedimentary units. GPR sends electromagnetic pulses into the subsurface that reflect off changes in the dielectric properties of sedimentary layers which are then received by an antennae and stored. A pulseEKKO 1000 GPR system was used with high frequency antennae (225, 450, and 900 Mhz). Step size and antennae separation were adjusted based on antennae frequency. Common mid-point surveys were collected to provide near surface velocity information and to calculate depth of radar reflections. Topographic measurements were recorded using a TopCon laser level to geometrically correct the profile over the beach ridge. Data was processed and plotted with pulseEKKO Software. Over the beach ridge, two transects were collected to allow for a comparison and to correlate with a vibracore hole. The more Westerly line was 100 m while the easterly line was 65 m long. A good depth of penetration was produced with high resolution datasets (2-5 m depending on antennae frequency). The detailed stratigraphy and interpretation provide a better understanding of beach forming processes of this Nipissing beach ridge located along the Huron Mountains.