3D MORPHOLOGY OF DRUMLINS WITHIN THE GREEN BAY LOBE DRUMLIN FIELD IN SOUTHEAST WISCONSIN

The Green Bay Lobe (GBL) of the Laurentide ice sheet produced drumlins in southeast Wisconsin that are used in the development of GBL reconstructions. However, inadequate data on spatial variability in drumlin morphology necessitates researchers to make simplifying assumptions about drumlin formation. This lack of data has limited the ability of past researchers to resolve temporal and spatial ice-flow direction variability of the GBL. A better understanding of drumlin 3D morphology will improve our ability to constrain the basal process of the GBL, resolve paleo GBL movements, and constrain the processes that lead to drumlin formation.

We used LiDAR derived DEMs of the area covered by the southern GBL to map all potential drumlins. We were able to interpolate the elevation data for each drumlin through the application of a MATLAB spatial analysis program we constructed. We then determined the best-fit of an ellipsoid to each drumlin 3D representation to provide optimum length, width, and height components and resulting misfit residuals. Using these best-fit criteria we then calculated height – length – width ratios of each drumlin’s best fitting ellipsoid. Variation in drumlin shape and ratios were compared to other factors that vary spatially such as ice advance phase, bedrock geology, depth to bedrock, and local slope to determine the relative importance of each factor.

We mapped 13,314 drumlins in the southern footprint of the GBL. At this stage, investigation into any statistically significant correlation between drumlin 3D morphology and factors that may have influenced spatial variations is underway. Our preliminarily results indicate that time under the ice is the primary control on drumlin shape but surprisingly the ratios do not vary monotonically towards the terminal moraine, as would be expected if that was the only significant factor. Rather, “pockets” of drumlins can exhibit different ratios associated with local factors (e.g. depth to bedrock) indicating that strong local factors can overwhelm the dominate control of time under the ice. We aim to determine the dynamic primary and secondary controls dictating 3D drumlin morphology and how their relevance varies spatially to better constrain GBL advance history.