REFINING THE LATE HOLOCENE OUTLET PALEOHYDROGRAPH FOR LAKE MICHIGAN-HURON WITH THE IPPERWASH PALEOHYDROGRAPH OR CLOSEST AND MOST COMPLETE STRANDPLAIN OF BEACH RIDGES TO THE OUTLET

In the Laurentian Great Lakes studying the natural history of prehistoric lake levels preserved in strandplains of beach ridges helps determine the context for current lake levels and predict potential future lake level changes. In particular, discerning the timing and amplitude of past lake-level fluctuations assists in reconstructing a relatively long-term framework of natural trends and patterns. Published strandplain data from Fort Gratiot, Michigan near the outlet for Lake Michigan-Huron records lake levels fluctuations from approximately 6,000 to 3,700 calendar years ago (Thompson et al. 2014) and has been used to adjust the outlet paleohydrograph reconstructed from five strandplains around Lake Michigan (Baedke and Thompson 2000, Argyilan et al. 2018). The newly collected strandplain data from Ipperwash, Ontario near the outlet for Lake Michigan-Huron chronicles lake level fluctuations from approximately 3,500 to 700 calendar years ago. This presentation compares the recently adjusted Lake Michigan-Huron outlet paleohydrograph to the site paleohydrograph reconstructed from the Ipperwash stranplain. Comparison of lake level elevations are used to estimate the rate of glacial isostatic adjustment, evaluate potential changes in lake water volume related to climate and changes in outlet location or conveyance during the Late Holocene near this important outlet of Lake Huron-Michigan.