MAPPING PAST TRIBAL CEMETERY USE AND POSSIBLE FUTURE DEVELOPMENT IN LAKE HURON SHORELINE SEDIMENTS USING GROUND PENETRATING RADAR

A tribal cemetery is interested in identifying areas where the cemetery can expand without disturbing potentially old, unmarked burial sites. A 250 MHz Ground Penetrating Radar (GPR) system, along with schlumberger and dipole-dipole electrical resistivity arrays, were used to determine regions in the cemetery that are undisturbed by human activity. GPR depth slices show higher reflections due to sandy horizons or objects in the subsurface. A variety of known graves were included within the survey region to determine what the anomaly characteristics are from different grave sites. Older graves (100 years old or so) have less prominent signatures than more recent graves, especially recent grave sites which use modern caskets and a burial vault. The modern anomalies have very sharp boundaries and distinct reflections. These are most likely due to differences between the GPR characteristics of shoreline sediments and the casket and vault materials or between the sediments and the void spaces within the casket or vault. Older graves were recognized by more subtle disruptions in natural sedimentary GPR reflectors. GPR was generally more effective than resistivity in delineating regions in the cemetery that have not been disturbed by human activity such as burials.

There are linear reflective GPR features within 1.5 feet of the current earth surface which span the width of the cemetery in a Southeast-Northwest direction. Coring of the more reflective and less reflective regions suggest the more reflective regions have a higher percentage of sand. These reflective features are approximately parallel to the current Lake Huron shoreline which is approximately 50 meters to the south and are likely older shorelines from when the cemetery region was at a lower elevation prior to glacial rebound. This study effectively identified areas of the tribal cemetery which are available for future expansion and will permit continued development of the cemetery. Additionally, the study determined the location of previous Lake Huron shorelines and the GPR and physical characteristics of these ancient shorelines.