SEDIMENT CHARACTERISTICS OF THE UPPER UNITS OF LANDSLIDE-PRONE BLUFFS ALONG THE SOUTHEAST SHORELINE OF LAKE MICHIGAN

Wave and groundwater action has caused immense coastal erosion leading to major landslides along the Lake Michigan shoreline. This results in high bluffs of exposed glacial material composed of sand, clay, and till. My research goal was to understand the characteristics of these sediments in each layer of the failed bluffs. Ground penetrating radar (GPR) provides a geophysical method for understanding the shallow sub-surface. Using 200 MHz antennas with a separation of 0.5m and step size of 0.1 m, data was collected along two transect lines (one perpendicular and another parallel to the shoreline) across three failed bluff sites. Results showed at least two distinct geological units with sandier material overlying finer material. Strong GPR reflections occurred in sandier soils while fine-grained soils, with higher clay and silt content, cause weaker reflections and GPR signal attenuation. Confirmation of these units comes from additional datasets such as moisture content, mean particle size, and visual observations. A comparison with soil survey data indicates that geologic units correspond with specific glacial depositional environments and can be successfully differentiated in GPR data in the uppermost bluff sediments.