Standing at GZ, cast your gaze to the south and a bit to the west. Some 14,000 years ago, the head of this shallow south sloping valley would, within a matter of a few days become a lake so large that the opposite shore could not be seen.
Now close your eyes for a few seconds. When you open them, imagine you live in the world of 12,000 BC. The glaciers have just recently retreated from the ground on which you’re standing. The elders still talk about the wall of ice when gathering at the evening fire. That wall is gone now, but the land is littered with its glacial rock debris. There’s little vegetation, some short grasses and trees of mostly birch and aspen, with spruces just beginning to appear.
You are a nomadic hunter, part of an extended family tribe, and the first people to this land. Stalking down the large mammals that inhabit this world, mammals that for the most part will be extinct in a few thousand years, fills your days. Your tribe follows the seasonal migrations of the animals that sustain you. Your weapons are crudely flake pointed spears and atlatls. The bow and arrows will be something your distant descendants invent. The clothes you wear, when you do wear them, are untanned animal hides, the same type of hides used to cover your simple dwelling.
Then one day as you are walking across this land, you notice a body of water to the south that wasn’t there yesterday. Three days later, Lake Wauponsee is lapping at your feet. Three weeks after that, the lake is gone. Had it really been there, or was it just a dream?
As the last ice age, “The Wisconsin” was winding down; the glaciers retreated to the northeast. These glaciers, known as lobes, retreated at different rates and as they retreated they dropped all the rocks, gravel and sand they had picked up on their journey from Canada. This debris formed ridges behind the glaciers and is called moraines. One particular glacial lobe, the Saginaw, dumped an inordinate amount of debris in its retreat across southwestern Michigan. Then an exceptionally warm period began melting the Saginaw lobe at an increased rate. The glacial water pooled up behind the moraine ridges until they could not contain them any longer.
The Torrent Begins
The dam had burst! A wall of water carrying all sorts of debris came down the Kankakee River, scouring the riverbed as it rushed to the west. As the Torrent entered the Illinois River valley, the water began to back up and flood the surrounding plains. Lake Wauponsee was the largest of these temporary glacial lakes.
The Glacial Lakes Formed by the Torrent
The modern channel of the Illinois River was carved by the Torrent. Because of the manner of its formation, the Illinois River runs through a deep canyon with many rock formations. It has an “underutilized channel”, one far larger than would be needed to contain any conceivable flow in modern times. Starved Rock and its several canyons were created by the Torrent.
Starved Rock
The waters of the Torrent carried tremendous volumes of sand and gravel downstream to the “Big Bend” at Hennepin where the river channel is narrow and entrenched in bedrock. Here the river valley widens to the south where much of the sand and gravel settled out, creating the “Sand Bars of the Illinois”.
The Illinois River south of Hennepin follows the ancient channel of the.Mississippi River. The Illinoin Stage of the Wisconsin Ice Age, about 300,000 to 132,000 years ago, blocked the Mississippi near Rock Island, diverting it into its present channel. After that stage melted, the Illinois River flowed into the ancient channel. The Hennepin Canal roughly follows the ancient channel of the Mississippi to upstream of Rock Island.