DOMINANCE OF STRONG NORTHWEST WINDS ACROSS THE MIDWEST IN THE POSTGLACIAL PERIOD (Invited Presentation)

Decades of on-the-ground geomorphic data point to eolian erosion and subsequent transport across many areas of the upper Midwest of the United States. These events span the last postglacial period and extend into the early Holocene. With the exception of easterly and northeasterly winds close to the ice margin, perhaps part of a glacial anticyclone, most of the strongest winds on the recently deglaciated upper Midwest were from the west-northwest. Both loess and dune records support this assertion.

After summarizing some of the better-known examples of eolian landforms (mainly dune fields in Wisconsin and Michigan) that developed on NW winds, we add some new data to the discussion. Particularly, we use examples from western and central Wisconsin and Michigan’s Upper Peninsula (UP) to point to both eolian erosion and transport across the region. In the UP, thin loess deposits occur southeast of dunes on the Glacial Lake Algonquin plain. The dunes in this area stabilized during the climatically dry, early Holocene, 8.2 to 8.6 ka. Dates on the loess match this interval, or are slightly older. Spatial patterns of loess texture and thickness data indicate transport on strong west-northwest winds. In western and central Wisconsin, considerable eolian evidence from several different types of settings and features, e.g., longitudinal, parabolic and clifftop dunes, as well as loess textures and distribution within broad transportation surfaces, again point to deflation and transport of eolian sediment on strong west-northwesterly winds. Key to future research will be dating of these features/sediments, to better establish the window within which these winds dominated the landscape.