Pleistocene Geology of the Lake Superior Region


    During the Pleistocene there were repeated glaciations over the North American continent. The Great Lakes were formed by these glaciations.  Easily erodable materials and topographic lows influenced the glacial advances over the Great Lakes region.
    As the glaciers flowed over these areas they deepened the preexisting valleys and damned them with glacial deposits.  This is how the early lake basins formed. 
  • According to LaBerge (1994), the origin of Lake Superior began with a major river valley in the Keweenawan sediments in the Lake Superior syncline.  Advancement of the glaciers, deepened the basin to over 1,300 feet (LaBerge, 1994).  Glacial Lake Keweenaw (ancestral Lake Superior) formed as the Lake Superior Lobe of the Laurentide ice sheet, retreated.  Another advance and retreat of the glaciers led to the formation of Glacial Lake Duluth in the Lake Superior basin.  These Lakes had higher water levels than Lake Superior does today due to glacial meltwater at the time and isostatic rebound, which is the rise of the continental crust after the weight of the ice has been removed. 
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      These pictures were taken between Au Sable Point and the Grand Marais in the upper peninsula of Michigan.
       
       
       
       
       
       
       
       

        References
       
       
       
       

      LaBerge, G. L., 1994, Geology of the Lake Superior region: 
      Geosciences Press, Inc., Tucson, AZ, 313 p.