PRELIMINARY ANALYSIS OF MULTI-DECADAL LAKE LEVEL FLUCTUATIONS CHRONICLED IN STRANDPLAIN STRATIGRAPHY: INSIGHTS FROM IPPERWASH, ONTARIO, CANADA

Beach ridges in the Great Lakes are depositional coastal landforms that chronicle multi-decadal lake level fluctuations and variations in sediment supply. To reconstruct the natural rhythm of lake level through time, a strandplain of multiple beach ridges are analyzed. Lake levels are influenced by glacial isostatic adjustment (GIA), natural climate patterns and outlet conveyance, therefore, multiple strandplains in a given basin are required to extract unique rates of GIA at each site and reconstruct climate-driven lake level patterns. Clues to past outlet conditions including location and depositional/erosional trends within the outlet are also preserved. Lake Huron’s outlet lacks any regulatory structures making the outlet potentially susceptible to changes in discharge through natural erosion or deposition. The Ipperwash Beach strandplain, in southern Lake Huron, is the closest preserved strandplain to Lake Huron’s modern outlet and provides the best record of the condition of this outlet through time. The Ipperwash Beach strandplain is located between Kettle and Stoney Point, ON and is composed of at least forty beach ridges. To fully analyze the Ipperwash Beach strandplain we combined multiple field technique. Ground penetrating radar (GPR) is used to image the subsurface stratigraphy between multiple beach ridges on the strandplain, surveying to determine precise elevations, vibracoring to determine the elevation of the ancient lake level, and optically stimulated luminescence (OSL) dating to determine the age of beach ridges. Over one km of GPR data, two km’s of topographic surveys, forty cores and ten OSL samples have been collected and are being analyzed. Preliminary results show the effectiveness of using sedimentary deposits, preserved in the Ipperwash Beach strandplain, to identify natural multi-decadal lake levels, estimate rates of glacial isostatic adjustment and gain insights into outlet conveyance. We present our preliminary results showing the natural rhythm of Lake Huron’s lake level fluctuations and the potential changes on outlet morphology. The information gathered in our study is required to make effective and informed decisions for Lake Huron’s outlet and stewardship of the Upper Great Lakes.