Classification and Distribution of Major Dune Types
There are four distinctive types of dunes encountered in Michigan: parabolic, perched, linear, and transverse. The first three dune types are commonly associated with the present Great Lakes shoreline, while transverse dunes are more often associated with large bays of Glacial Lake Algonquin, from about 11,000 years ago. Linear dunes have also been called dune-and-swale complexes. Several classifications of sand dunes identify several more categories than the four listed here. Some of these studies are listed at the end of this publication for further reference.
While the shape of each dune type differs, the general cross-section of all dune types has similarity. The slope on the windward face of a dune is gentle, usually not over 15 degrees. In contrast, the slope of the back or lee side of the dune is much steeper, sometimes approaching the "angle of repose" of dry sand. The lee slope is steep enough that climbing it can be exhausting and typically results in considerable erosion of the slope.
Parabolic dunes, defined by their distinctive U-shape, are found only in moist environments, where extensive vegetation cover often stabilizes the dunes.
Perched dunes, restricted to the northeastern shore of Lake Michigan and to Lake Superior, are perched atop glacial moraines that have bluffs 90 to 360 feet above the present lake level.
Large complexes of linear dunes form the shoreline along numerous Great Lake bays. These complexes consist of a series of roughly parallel dunes that form as the water level of the Great Lakes gradually drops.
Transverse dunes, linear to scalloped in shape, are believed to have formed in shallow bays along the edge of the glaciers. They are 30 or 60 feet high and are surrounded by shallow peatlands.