Wilderness Underfoot: The glaciers' bounty

Thanks to the glaciers, Illinois has a wealth of sand and gravel deposits

Dig a few feet down into any soil in our state, and you’re likely to reach a layer of crushed rocks, gravel, sand and clay. This material, left by Ice Age glaciers, is known as glacial till. Much of it was scoured from the surface of our northernmost states and Canada, and then dragged hundreds or thousands of miles south by enormous sheets of flowing ice. As the glacial ice melted, it dumped the till atop existing soil and bedrock. Piles of this material, in long rows, are called moraines, and they can be easily spotted on relief maps of this region.

Our sand and gravel resources have important economic uses. These raw materials are used as aggregate in the production of concrete, portland cement, mortar and plaster. They’re also widely used as fill for roads and building foundations. Illinois ranks in the top 10 sand and gravel-producing states, with more than 45,000 tons extracted each year.

The mining of glacial deposits is not without controversy, however. Much of our richest sand and gravel deposits occur in the state’s heavily populated Chicago metropolitan area. In many communities, gravel trucks are considered a nuisance, creating noise and sometimes leaving trails of sand and gravel (and, occasionally, broken windshields) in their wake. And there are important environmental concerns regarding open-pit mining, which drastically alters the landscape and may impact groundwater. When a mine closes, some sort of rehabilitation must take place, perhaps allowing it to be converted into a lake or park.

From the Feb. 21-27, 2007, issue

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