Coastal dune environments of southeastern Lake Michigan; geomorphic histories and contemporary processes

This field guide discusses the dune types and processes, ecology, and geomorphic history of the largest freshwater dune systems on the southeastern shore of Lake Michigan. From north to south, stops include P. J. Hoffmaster State Park, Gilligan Lake/Green Mountain Beach Dune, Saugatuck Harbor Natural Area, and Grand Mere and Warren Dunes State Parks, Michigan. All of the sites are low, perched transgressive dune complexes. Moving from the lake inland, the typical dune complex in this area consists of incipient foredunes, an established foredune ridge, a parabolic dune complex, and a back-dune ridge complex. All stages of ecological succession are typically present in the larger dune complexes. Surface changes in Lake Michigan dunes are driven by spatial gradients in sand flux, which, in turn, are determined by a complex interaction among wind dynamics, vegetation patterns, and preexisting topography. Surface change patterns are modified by seasonal effects, with the majority of sand transport being associated with strong storms in the autumn, winter, and early spring. Sand can be temporarily stored in niveolian deposits during the winter, leading to oversteepened slopes, which collapse during the spring thaw. Current dune complexes largely formed during and after the rise in lake levels to the Nipissing high lake level, ca. 4.5 ka. Broad fields of relatively low dunes developed during the lake-level drop following the Nipissing high. Beginning with the rise to the Algoma high lake level, ca. 3.2 ka, the lakeward edges of these fields were episodically reworked, forming large parabolic dune complexes. A period of widespread dune stability formed the Holland Paleosol, a spodic inceptisol. Dune growth and migration resumed prior to European settlement of the area and continues today. Foredune complexes grow wider and higher during periods of low lake levels, but narrow during periods of high lake level due to scarping at their lakeward edges.