Geological Features of Ice Ages in Ohio

My family moved from Ohio to Georgia during 1976 when I was 13 years old. I occasionally wonder how my life would have been different if we never would have moved. Would I have a blog entitled Ohio Before People instead of Georgia Before People? My interest in Pleistocene mammals began before we moved when I read a Time Magazine article about saber-toothed cat bones found at the First National Bank Site in Nashville, Tennessee. Maybe I would’ve had a natural history blog focusing on Ohio instead of Georgia.

Evidence of Pleistocene Ice Ages is abundant in Ohio because glaciers repeatedly advanced and receded over the state. Scientists believe there were 17 major glacial advances in Ohio over the past 3 million years, but geological evidence exists for just the last 2–The Illinoian (230,000 years BP-132,000 years BP) and The Wisconsinian (118,000 years BP-11,000 years BP). These last 2 glacial advances scoured away geological evidence of the previous 15, and the only geological evidence of the Illinoian glacial advance is south of where the glacier advanced during the Wisconsinian Ice Age. During the Illinoian Ice Age the glacier advanced all the way into northern Kentucky.

The following is the geological evidence of Ice Ages in Ohio.

Map showing the maximum extent of the most recent glacial advance during the Wisconsinian Ice Age. During the previous Ice Age, The Illinoian, the glacier advanced even further into northern Kentucky.

Lake Erie

All the Great Lakes were formed from melted Ice Sheet. Before Ice Ages began, the now extinct Erigan River System flowed through where the Great Lakes exist today. The advancing glacier took the route of least resistance and scoured out lake basins in this former river valley. There is no evidence of Great Lakes following previous Ice Ages, but it is likely there were previous incarnations of the Great Lakes. Present day Lake Erie is only 5000 years old, and it evolved from previous post-glacial lakes.

Kettle Lakes

Punderson Lake, a kettle lake in Ohio. Our family went for a picnic here in 1967 when I was 5 years old. A kettle lake is a melted chunk of glacier left behind when the glacier retreated.

Ohio is dotted with kettle lakes. They were formed when the glacier retreated but left big blocks of ice behind in low lying areas. Sometimes these blocks of ice became buried in sediment. Eventually, this melted ice became a small lake.

Kames

A kame in Scotland. (I couldn’t find a good photo of 1 in Ohio). Kames are sandy knobs that were outwash of sediment carried by meltwater streams on top of the glacier. When the glacier underneath melted, they slumped, but many are still higher than the surrounding terrain.

When the glacier was in the process of retreating, meltwater floods and wind often carried sediment on top of the ice sheet. This sediment piled up into hills. Eventually, the ice underneath melted, and the sediment slumped but was still higher than the surrounding terrain.

Moraines

Diagram showing sediment pushed forward by a glacier and left behind after it recedes.

Moraines are sediment pushed in front of glaciers. They appear as hills and show how far the glacier advanced. Glaciers alternately advanced and retreated. The most southerly moraines in Ohio show the farthest extent of glacier advance during the Last Glacial Maximum. Recessional moraines show where glaciers re-advanced during cold climate fluctuations after the Last Glacial Maximum. Spruce tree logs are commonly found buried in the moraines, showing where glaciers rapidly advanced through forests.

Outwash

The glaciers often melted rapidly, and the meltwater flooded down stream and river valleys carrying loads of sediment including gravel and sand. This sediment can be found in stream-like patterns throughout the state, though they are covered with vegetation. There are also lake sediments where the glacier blocked streams and rivers, forming temporary glacial lakes that eventually drained.

Erratics

Erratics are large boulders left behind by retreating glaciers. They are usually rocks not found in the region.

The glacier pushed big Canadian boulders into Ohio, leaving them behind when the ice melted. The big rocks do not match the local geology. The only Cambrian-aged rocks found in Ohio originated from Canadian outcrops.

The Shape of the Ohio River

Before Ice Ages began most rivers and streams in Ohio flowed north. But glaciers blocked the flow and forced the rivers to change course. The Ice Sheet shaped the course of the Ohio River which was actually created during the Ice Ages. Glacial advance extinguished a major Pliocene-aged river system known as the Teays. See also https://markgelbart.wordpress.com/2015/05/15/glaciers-shaped-the-ohio-river/

Reference:

Camp, Mark

Roadside Geology of Ohio

Mountain Press Publishing 2006

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