CHARACTERIZATION AND MAPPING OF PALEOLAKE ALGOMA SHORELINE SEDIMENTS IN GRAND PORTAGE NATIONAL MONUMENT, MINNESOTA

At the end of the last glacial maximum, meltwater from the retreating Laurentide Ice Sheet brought about higher-than-present water levels in the Lake Superior basin. As lake levels fell over time, shoreline features such as beaches, terraces, and wave-cut cliffs remained as strandlines on the landscape. Advances in remote sensing and mapping technologies have allowed for increasingly thorough surveys of strandlines and their associated paleolakes throughout the Great Lakes. However, remotely characterizing the sedimentological nature of these features remains a challenge.

For this project Geographic Information Systems (GIS) and ground truthing methods were used to map and characterize paleolake shorelines in Grand Portage National Monument. Visible strandlines were identified throughout the park using Light Detection and Ranging (LiDAR) imagery. Strandlines were correlated to paleolakes based on previously modeled elevations. GIS was used to create shapefiles of the shoreline locations based on their approximated elevations. During the 2020 field season, Paleolake Algoma (~3,000 cal. yr. B.P.) was selected as the focus for ground truthing. Sediment transects were cored along the modeled shoreline, and described in the field. Sandy sediments were identified as likely shoreline-related, and samples were collected. Due to the shoreline’s location within the original village of the Grand Portage Band of Ojibwe, archaeological surveys were also completed.

Additional sediment and GIS analyses are ongoing. Grain size distribution analyses are being completed to determine whether samples indicate deposition in high or lower energy environments. These results will be mapped using GIS, and analyzed to determine spatial patterns. To assess whether sediment disturbance has occurred due to human occupation, lithologic studies of sand samples are taking place to discern differences between sediments collected from artifact-positive test pits and those from artifact-negative pits. We plan to include the results of this study in a predictive model that will eventually be developed for archeological sites along the north shore of Lake Superior in Minnesota.