EXPLORING THE POTENTIAL LINKAGE BETWEEN COASTAL SAND DUNE ACTIVATION AND DROUGHT EPISODES IN THE NORTHERN LAKE MICHIGAN BASIN

Coastal sand dunes dominate the Lake Michigan shore in Michigan. Recent research has focused on the age and formation of coastal dunes in the northern part of the basin through OSL dating of eolian sands. These studies reveal that most dune growth occurred in two phases; the first between about 3500 and 2000 years ago, with peak sand movement taking place toward the end of this cycle. Following a period of reduced sand supply, the next episode of dune mobilization began about 1000 years ago and lasted for around 500 years. Most dune growth occurred during this latter phase of activation, which correlates to a period of extensive dune growth in the southeastern part of the Lake Michigan coast. Past studies of Lake Michigan coastal dunes have linked periods of dune growth largely to high lake phases and their effects on coastline destabilization. While this association may be partially valid, our work also suggests that the most intense periods of dune activation in the northern end of the basin correlate well with intervals of regional drought. In particular, the onset of dune growth at 1000 years ago coincides with the Medieval Warm Period (MWP), which coincidentally was a time of intensive drought and dune activation in the Great Plains and elsewhere. While dune activation in the semi-arid/sub-humid Plains at this time is clearly linked to landscape destabilization due to reduced vegetation, the role of drought on coastal dunes in the more mesic Great Lake region is altogether unclear. This paper explores the potential role that drought plays during these episodes, including 1) rapid fluctuations in lake level, with increased amounts of sand made available during wet periods that are mobilized during dry episodes; 2) increased intensity of westerly winds, which are thought to have been stronger during the MWP, and 3) devegetation of wetlands, thus providing a sand source.