INCORPORATING GEOLOGIC KNOWLEDGE TO BETTER UNDERSTAND THE COASTAL ZONE IN THE LAURENTIAN GREAT LAKES

The coastal zone of the Laurentian Great Lakes (LGL) is a dynamic and complex area of interest to more than 30 million people that live along this world-recognized waterway in the North American interior. Natural processes from air, water and land and anthropogenic activities contribute to the coastal zones’ complex dynamic nature. To fully encapsulate coastal zone dynamics requires spatial and temporal understanding of a multitude of processes, both at local and lake-wide scales over time periods influenced by humans and the natural realm. In the LGL, we currently define the coastal zone using contemporary conditions recorded by instruments, many extending back several decades and a few extending back to just beyond a century. Recognizing natural patterns and trends in these instrumental records is difficult because of the enormity of human impacts to paralic and atmospheric processes and the relatively short temporal record. To accurately recognize anthropogenic influence and separate out natural from anthropogenic change one needs insight into geological conditions and process before human impacts on the system. We assert that ancient relict shorelines of the LGL provide that necessary geological insight by preserving the most detailed record of natural conditions. Sedimentology and geomorphic characteristics of LGL shorelines deposited within the last five millennia reveal three superimposed quasi-periodic oscillations in lake level linked to climate, unidirectional ground-surface flexing within and between lake basins due to glacial isostatic adjustment, and natural changes in outlet conveyance. Incorporating these new components will better constrain our understanding of the human manipulation of the natural system.