Remember Fred Flintstone, he was always blaming poor Wilma for all the stupid situations he and Barney had gotten themselves into. Well, unfortunately Fred can’t blame the Ice Age on Wilma this time. As we discussed in Part One of the geology of Ohio, the concept of geologic time was explained as well as the “Periods” that led to the formation of what we call Ohio today. However, there is one more critical event, which like a sculptor chiseling away at a marble block to create a beautiful statue, reshaped the Ohio landscape for eternity…or for now, anyway.
About 2.5 million years ago, the earth began to cool and we entered the Pleistocene period on our geologic time line, commonly known as the Ice Age. Huge sheets of ice called glaciers began their slow decent southward. Reaching down from Hudson Bay, and covering most of Canada, it reached the southern borders of Ohio. No one knows for sure how many ice sheets advanced and retreated over time. Evidence of each glacial event was removed with subsequent glacial activity. The size, scope, power, and magnitude of glacial events are almost incomprehensible. The coastline of Maine in Acadia National park, the Yosemite Valley in California, and the Great Lakes are all the work of glaciers. 230,000 years ago the Illionian glacier covered all but the 20 southeastern counties of Ohio, what is called the Unglaciated Allegany Plateau. The Great Miami, Little Miami, and the Scioto river valleys were carved out by this glacial event. 40,000 years ago the massive Wisconsinan glacier covered much of the same area as the Illionian, but it ranged from 5000 to 8000 feet thick. It took 12,000 years to cover Ohio. Moving between 170-360 feet per year, this glacial event completely reshaped Ohio’s terrain. So great was the power of this glacier, the shore line of ancient “Lake Erie” was 230 feet higher than it is today. It changed the course of the Cuyahoga River and carved the Grand River Valley. 19,000 years ago the earth began to warm and the glacial activity in Ohio came to an end. It took 5000 years for the glacier to retreat, leaving vast quantities of material called till. Glacial till comes in all shapes and sizes, ranging from 50 ton boulders to fine sands and clay. Till is the parent material of much of Ohio’s soil. Many of the rocks found in till are “foreign” to Ohio and are unlike any bedrock formations found in Ohio. The round granite boulders and quartz that we commonly see in fields or as landscape rocks are called “glacial erratics” and have their origins in Canada. Another way to remember is the old saying “Ohio flats (shale) and Canada fats (granite). On average, material deposited by the glacier was 100 feet deep and in some areas up to 700 feet deep. Gently rolling terrain resulting from glacial till is called ground moraines and end moraines. This is believed to be the southern edge of the glacier. This can be seen throughout central Ohio. Other types of deposits are called a kames, eskers, and outwashes. Kames are mounds of sand and gravel deposited by melt water flowing across the ice and pouring its contents into holes and crevasses along the edge of the ice sheet. Eskers are ridges of sand and gravel deposited within the ice sheet in tunnels formed by melt water; as the glacier melted, these ridges were left. An outwash is the term used to describe the vast amount of sand and gravel that flowed south through the Hocking, Muskingum, and Scioto watersheds. These are responsible for the large deposits of sand and gravel in our area and throughout Ohio. Evidence of glacial remnants can be seen throughout Geauga and Portage counties with the huge sand and gravel quarries that dot the countryside. In addition, Bass Lake and Burton Wetlands are referred to as “kettle” lakes. These lakes were formed when huge blocks of ice detached from the glacier and became lodged in the sediment. When the ice melted the depression filed with water creating the lake.
It is our hope that you now have a new “lenses” with which you look at Ohio’s landscape, from the names of towns to the very ground we stand on. As winter turns into spring, we encourage you to go out and enjoy Nearby Nature.