GEOMORPHIC EVOLUTION OF COASTAL DUNE FIELDS IN THE NORTHEASTERN PART OF THE LAKE MICHIGAN BASIN: THE RELATIONSHIP TO LAKE LEVELS AND ISOSTATIC REBOUND

Coastal sand dunes are very common around Lake Michigan. Abundant research demonstrates that dunes along the southeastern shore of the lake began to form ~ 5 ka during the Nipissing stage of Lake Michigan. Since that time the dunes underwent episodic vertical acreation with several distinct periods of stability indicated by buried soils. Blowouts have also formed in many of these dunes, resulting in eastward migration of eolian sand and distinct parabolic landforms.

Our current research in the northeastern part of the Lake Michigan basin indicates a different geomorphic history. Compared to the southern shore, Nipissing dunes are rare in the north and eolian landforms apparently grew horizontally rather than vertically. In the north, most major eolian deposition began after about ~3.2 ka and relates to a series of late Holocene lake transgressions. Large (~30-m high) dune ridges initially formed that rarely contain buried soils. These ridges are now far inland because subsequent transgressions built lower dunes shoreward. This pattern occurse because older beaches and dunes were isostatically raised during intervening regressions, which exposed progressively younger coastal surfaces on which dunes could grow. Several periods of dune growth have been identified during the late Holocene, including a widespread event at ~ 1 ka that may be related to regional drought.