EVIDENCE OF PRO-GLACIAL LAKESHORES IN THE HIAWATHA NATIONAL FOREST, UPPER PENINSULA, MICHIGAN

The eastern part of the Hiawatha National Forest (HNF), Upper Peninsula Michigan was glaciated during the Pleistocene with the final retreat ~11.7 ka. After the glaciers retreated, pro-glacial lakes formed in the area of the modern day Great Lakes. Lake Algonquin was present ~11 ka, immediately following the last glacial retreat, and had an elevation in the study area of 250-270 m amsl. Lake Nipissing was present ~4.5 ka and had an elevation in the study area of 185-195 m amsl. The bedrock geology of the region is primarily Silurian dolostones of the Manistique and Engadine Groups, which occasionally outcrop to form the Niagara Escarpment. This study focuses on identifying the pro-glacial lake beaches in the HNF, which are manifested as rocky benches and littoral caves.

The pro-glacial lake shores in the area are denoted by benches. These benches are identified in this region by small, sudden slope breaks, generally <10ft change in elevation. At ~250-270 m amsl, outcroppings of the Manistique and Engadine Groups are identified in situ, while immediately downslope “boulder fields” are present. These boulder fields contain >20 boulders in <0.25 acres and are made of both native boulders and crystalline erratics. These boulder fields are found within 10’s of feet to 100’s of feet from outcrops. Examples of the benches have been identified at both Lake Algonquin and Lake Nipissing, along with modern day Lake Huron.

Littoral caves are also present in the HNF in the Niagara Escarpment. These caves are believed to have been caused by the wave action of Lake Algonquin. Eight caves have been identified and mapped along Maple Hill, a hill that is part of the Niagara Escarpment. The morphology of these caves is simple, ovoid, and generally have progradationally collapsed roofs due to the thinly bedded Manistique Group that contains these features.