MODERN-, CENTURY-, AND MILLENNIAL-SCALE SHORELINE STUDIES IN THE UPPER GREAT LAKES (Invited Presentation)

Recent lake-level rises in the Upper Great Lakes have renewed interest in issues such as rates of bluff failure, beach recession and nearshore sediment transport. This presentation summarizes recent projects in collaboration with the Wisconsin Geological and Natural History Survey to understand geologic processes and the geologic history of Wisconsin’s Great Lakes shorelines. The geomorphic variability there provides excellent field laboratories including rocky and cohesive bluffs, beaches that range from sand-starved to sand-dominated, and low to high energy waves environments. In addition, straddling the 45^th parallel provides a winter climatic gradient with persistent shore ice along Lake Superior and temporally variable shore ice in Lake Michigan. We are engaged in modern process studies focused on bluff failure, bar and beach evolution, and shore ice/sediment dynamics that are supported with high-resolution spatial and temporal data such as in-situ measurements of bluff failure, cm-scale digital elevation models generated by structure-from-motion photogrammetry, remote camera monitoring of groundwater discharge, bathymetric surveys in areas of shoaling, site-specific wind and wave measurements, and field and laboratory experiments of shore ice. Tree-ring chronologies derived from historic structures exhibit patterns of correlation among reference chronologies of the same species and illustrate the excellent potential to develop a more complete network of sites with tree-ring data throughout the Michigan-Huron Basin by utilizing wood incorporated into historical structures. Optically-stimulated luminescence chronologies of barrier beaches and associated dunes document a major perturbation in sediment supply during the Nipissing highstand in the Door Peninsula, a sediment-starved system. Embayments there were permanently separated from Lake Michigan then, and dune development occurred rapidly when sand supply increased as lake levels fell.