Extensive loess sheet in NW Michigan illustrates river outwash processes. The main sources of loess sheet in NW Michigan are bare outwash deposits, till sheets, and floodplains along the windswept margins of advancing or retreating ice fronts, especially during the summer ablation season when outwash maximize and the landscape is neither frozen nor snow-covered. In many Michigan landscapes, the uppermost surficial deposit is a late Wisconsinan loess, the Peoria loess. In these areas, meltwaters ponded in front of the ice, allowing silts to settle out. Meltwater from the Outer Port Huron advance flowed into the Manistee River (Schaetzl 2007).
The Manistee River, therefore, is presumed loess source. Loess sheet in NW Michigan is wind-transported silt that is deposited as a poorly consolidated blanket whose thickness and grain size diminish downwind from source areas. As ice fronts retreated and vegetation invaded these source areas, loess deposition diminished and soil began forming. Loess accumulated through dry deposition of tropospheric dust (Garland 1955). Though readily observed on land, where it is trapped by plants and acquires cohesion from soil moisture and carbonate cementation, loess also settles through the water column of Lake Michigan.
Soils formed in the calcareous and nutrient-rich loess are typically highly fertile, though easily erodible by both wind and water. Bibliography Garland, John H. 1955. North American Midwest: A Regional Geography. Wiley: New York. Schaetzl, Randall J. 2007. The Buckley Loess Sheet in NW Lower Michigan: Evidence for a Manistee River Outwash Source. Geography, Michigan State University, [date last accessed 7 July 2008]. Available from World Wide Web: http://gsa. confex. com/gsa/2007AM/finalprogram/abstract_127735. htm