A CASE STUDY OF LAKE MICHIGAN DUNE DYNAMICS AS LAKE LEVELS CHANGE

On Great Lakes dunes, the link between dune dynamics and coastal processes is seen in dune responses to changing lake levels. This project investigates changes in dune dynamics over a multi-year period characterized by low lake levels (2000-2013), rising lake levels (2014-2019), high lake levels (2019-2021) and falling lake levels (2021-2022). The study location is an active beach-foredune-blowout system in P.J. Hoffmaster State Park on the east coast of Lake Michigan, where field data has been collected since 2000. Dune dynamics are measured with direct observations, photographs, erosion pins, topographic surveys and GPS mapping. Variables measured at the site include surface conditions, vegetation and wind speed and direction. Regional climate and lake-level data are obtained from established data collection programs.

Results show that dune dynamics were characterized by foredune growth during the period of low lake levels, with net movement of sand from beach to foredune. During rising and higher lake levels, wave erosion at the lakeward edge of the foredune (2014-2019) and dune ridge (2019-2020) moved sand from the dunes to the beach. Although scarping exposed sand previously stabilized by vegetation, little sand moved by wind into the dune system. As lake levels dropped following a peak in 2020, sand ramps began to build against the dune scarps. From 2021 on, the blowout and dune ridge have been in a period of heightened activity including sand transport onto the dunes from the beach via sand ramps, higher rates of slipface deposition and blowout advance, and sand transport/deposition tens of meters further into the dune system compared to pre-2021 locations.

Dune measurements through different parts of the lake-level cycle (low, rising, high, and falling) are providing opportunities to fill in details for simple explanatory models such as equating high lake levels with increased dune activity. For example, the recent increase in dune activity is a combined response to the destruction of the foredune during higher lake levels and the building of sand ramps during subsequent falling lake levels. If lake levels continue to drop, the creation and growth of a new foredune will at some point cut off the current sand transport pathways from the beach onto the blowout and further inland.