Glaciation and its Effects on Landscapes-Approaching-03

Grinding, Shaping, & Deposition

It is hard to imagine a sheet of ice over a mile thick, but that is what happened. As the glaciers grew and pushed their way southward, they carried with them large amounts of debris. This debris in the giant sheets of ice scoured, or abraded, the landscape as they moved. Abrasion occurs when glaciers scrape over Earth’s surface. The glacier and the debris they carried act like sandpaper. The moving glacier contains sediments and rocks frozen in the ice. The rocks and sediment grind away leaving some of the features we now see.

While glaciers eroded the landscape, they also left behind much of debris they had picked up. When the glaciers finally retreated, they melted and released the debris. This debris left behind by the melting glaciers is called glacial till. This material, carried by meltwater, filled in the regions that were once hill and valley terrain. This is what created the flat landscape you see today.

This ground up debris of gravel, sand and clay, which in places are hundreds of feet thick, became the parent material for today’s rich soils. As the glaciers continued to melt, the sediments they carried filled the river systems. It was this fine silt that was later blown onto the plains by the westerly winds that provided Illinois and the other neighboring states with rich topsoil.