Wind Erosion and Sand Dune Formation on High Lake Superior Bluffs

The Grand Sable Dunes and the Sleeping Bear Sand Dunes are the largest fields of active sand dunes in the Great Lakes. Both are situated along the crests of high bluffs which rise 40-90 m above the lakes and are composed of sandy glacial deposits. Annual rates of wind erosion of sand from the Grand Sable bluff face have been estimated from sand deposits interbedded with leaf litter on the forest floor adjacent to the dune field. Annual wind erosion increases linearly with slope height, reaching a maximum of almost 1 m 3 per m of distance along the strike of the bluff for a 90 m slope, and is concentrated in a belt along the brow of the slope. Despite the strength added to the slope by ground frost, most sand is eroded in winter. Sand, freed from the bluff by sublimation of ice, is transported into the dune field sometimes with snow sometimes without, depending on weather conditions. Groundfrost increases with distance up-slope, reaching a depth of several m at the crestslope. Frost depth is controlled by the rate of conductive heat transfer above the footslope where the ground is warmed by groundwater seepage. The annual flux of sand into the dune field for the period 1973-83 is estimated to be 6300 m 3 /yr. This rate of nourishment, however, varies with fluctuations in lake levels as they influence wave erosion, slumping and devegetation of the bluff.