MODELS OF HOLOCENE DUNE BUILDING APPLIED TO THE NORTHEASTERN SHORE OF LAKE MICHIGAN

Recent studies of coastal dunes of the upper Great Lakes have linked the building of foredunes and perched dunes with specific combinations of shore exposure, littoral sand drift, composition of lake-facing bluffs, and Holocene lake-level history. A 30 km stretch of Lake Michigan’s shore, northwest of the Mackinac Straits and normal to prevailing winds, includes examples of both dune types. How is it that disparate dune morphologies elsewhere linked with contrasting sources of sand supply and different behaviors during lake-level change occur here in close proximity? Along this stretch of shoreline, I located and recovered organic matter from buried soils within dune-fields at five locations and used standard methods of soil description and soil stratigraphy to characterize the context of sample sites. I then compared bathymetric and wind regime maps of Lake Michigan and dune-building patterns described from other studies with these soil burials. Within the five study sites, all soil burials occurred during lake high stands identified in beach-ridge studies within the Lake Michigan basin. Between study sites, however, recent as well as ancient dune building in accordance with Olson’s “foredune model” (wherein dune building occurs during falling lake levels) is evident. Examination of NOAA’s bathymetric map of Lake Michigan suggests that disparate styles of dune-building along this portion of the shore are controlled by the positions of off-shore shoals and islands. These barriers lie across the path of effective winds and strongly influence the frequency and severity of wave-driven disturbance during high lake levels. These results suggest that dunes of each portion of the shore are influenced by unique combinations of factors.