VOLUMETRIC ESTIMATES OF COASTAL SAND DUNES IN LOWER MICHIGAN: EXPLAINING THE GEOGRAPHY OF DUNE FIELDS

This study assesses the geography and volume of coastal dune sand along Lakes Huron and Michigan in Lower Michigan. Dune field extents were obtained from digital maps of critical dune area and soil parent material. Volumetric estimates were determined by establishing basal surface elevations and then calculating the average height of overlying dune deposits using digital elevation model (DEM) data within a raster GIS framework. Results indicate that similar to 1.8 km(3) of coastal dune sand occurs in Lower Michigan, with similar to 95% located along Lake Michigan due to prevailing westerlies. Most (similar to 80%) of eolian sand is contained within 10 dune fields. Six of these fields are along the northeastern coast of Lake Michigan where they are associated with embayments and headlands, suggesting that changing shore angles and sandy bluffs are important geographical variables. Dune fields along the southeastern shore generally line the coast for greater distances and contain smaller concentrations of eolian sand that may be partially derived from debouching streams. Differences in sand volumes between the northeastern and southeastern coasts of Lake Michigan may occur, in part, because (1) northern coastal surfaces continue to rebound isostatically, resulting in progressively younger surfaces for dune growth, and (2) erosion in the southern end of the basin has removed dune deposits.