A POTENTIAL CLASSIFICATION SYSTEM FOR COASTAL SAND DUNES ALONG THE EASTERN SHORE OF LAKE MICHIGAN

The coastal sand dunes along the eastern shore of Lake Michigan collectively form the largest body of freshwater dunes in the world. In northwest Lower Michigan the larger dunes tend to occur in isolated fields that mantle high bluffs. South of Manistee they cover topographically low lake planes and occur in semi-continuous fields that line the shore for many kilometers. Recently obtained radiocarbon data indicate that most dune growth occurred between about 5500 and 2000 cal. yrs B.P. The term perched dunes is usually associated with the more northerly dunes, whereas dunes to the south have been called a variety of things, including high dunes, cliffed dunes, secondary dunes, and barrier dunes. Regardless of the terminology, all large dunes commonly share 1) a parabolic form, 2) transgression across older geomorphic surfaces, and 3) appear to have grown mostly during high lake stages as per the perched dune model. In an effort to simplify classification, all large dunes can be included within a single category of transgressive dunes that is further subdivided into two categories: 1) high perched dunes and 2) low perched dunes.