Lake Erie - Geology

Geology

Lake Erie in its current form is less than 4,000 years old, a short amount of time geologically speaking. Before this, the land on which the lake now sits has gone through several complex stages. A large lowland basin formed over two million years ago as a result of an eastern flowing river that existed well before the Pleistocene ice ages. This ancient drainage system was destroyed by the first major glacier in the area, while at the same time deepening and enlarging the lowland allowing water to settle and form a lake. The glaciers were able to carve away more land on the eastern side of the lowland because the bedrock is made of shale which is much softer than the carbonate rocks on the western side. Thus, the eastern side of the modern lake is much deeper than the western portion which averages only 25 feet (7.6 m) deep. Lake Erie is the shallowest of the Great Lakes because the ice was so thin and lacked erosion power when it reached that far south.

As many as three glaciers advanced and retreated over the land causing temporary lakes to form in the time periods in between each of them. Because each lake had a different volume of water their shorelines rested at differing elevations. The last of these lakes to form, Lake Warren, existed between about 13,000 and 12,000 years ago. It was deeper than the current Lake Erie, so its shoreline existed about eight miles (13 km) inland from the modern one. The shorelines of these lakes left behind high ground sand ridges that cut through swamps and were used as trails for Indians and later, pioneers. These trails became primitive roads which were eventually paved. U.S. Route 30 west of Delphos and U.S. Route 20 west of Norwalk and east of Cleveland were formed in this manner. One can still see some of these ancient sand dunes that formed in the Oak Openings Region in Northwestern Ohio. There, the sandy dry lake bed soil was not enough to support large trees with the exception of a few species of oaks, forming a rare oak savanna.