- Lake Chicago
Lake Chicago was a prehistoric
lake that is the ancestor of what is now known asLake Michigan , one ofNorth America 's fiveGreat Lakes .Origin
The city of
Chicago lies in a broad plain which, hundreds of millions of years ago, was a great interior basin covered by warm, shallow seas. These seas covered portions of North America from theArctic Ocean to theGulf of Mexico . Evidence of these seas are found in thefossil s ofcoral , such as those unearthed inIllinois quarries atStony Island Avenue , Thornton and McCook Avenues, or at 18th Street and Damen Avenue, all in Chicago. Evidence may also be found in the fossils in the Niagara limestone bedrock found throughout the Chicago area and extending all the way toNiagara, New York .Much later, the
polar ice cap crept four times down across the continent, covering the region with ice to a depth of a mile or more. As the climate changed, the ice melted; and the last great ice flow (theWisconsin Glacier of thePleistocene period, which covered much of northern half of North America) retreated, and an outlet for the melting water developed through the Sag River and theDes Plaines River Valley around Mt. Forest, Illinois, in the area known as the Palos. Mighty torrents of water poured through those valleys, eventually leaving behind them the prehistoric Lake Chicago, the ancestor of Lake Michigan.Size
Somewhat larger than Lake Michigan, Lake Chicago extended west to present day
La Grange, Illinois ; and south beyond Homewood andLansing, Illinois ; completely covering what is nowNorthwest Indiana , including the cities of Hammond andGary, Indiana .As the
Wisconsin Glacier continued to retreat, it created new outlets for the water in Lake Chicago, includingNiagara Falls , and theSt. Lawrence River . As these outlets were developed, the water level in Lake Chicago began to drop in three observable stages of 15 to 20 feet each. Eventually even the outlet to the southwest dried up, and the DesPlaines River overflowed into the basin that became Lake Michigan.Today
Vast amounts of sand in spits,
dunes and beach lines—particularly at the southern tip of Lake Michigan, in Indiana—were left behind by each of the three stages of lake level drop. Today, evidence of these vast sand deposits are still clearly visible. Northern Indiana, for example, contains some of the most beautiful beaches found in any of the five Great Lakes; and many of the Chicago area's trails and roads follow some of these ancient beach lines or ridges in the sand spits.For example, Ridge Road from Homewood, Illinois, through Thornton and Lansing, Illinois, is one; Michigan City Road through Riverdale, Dolton, and Calumet City, Illinois, is another; LaGrange Road is another; Riverside Drive in Riverside; Ridgeland Avenue in Oak Park, or Grosse Point Road, Carpenter Road, and Ridge Avenue through Evanston, Illinois, are some others.
Blue Island, Illinois , and Stony Island were, literally, islands left behind as Lake Chicago's water level fell.ee also
*
Lake Agassiz
*Lake Maumee External links
*Killey, Myrna M. 1998. Illinois' Ice Age Legacy. Illinois State Geological Survey GeoScience Education Series 14. 66 pages.
*Willman, H.B. 1971. Summary of the Geology of the Chicago Area. Illinois State Geological Survey, Urbana, IL. Circular 460. 77 pages.
* [http://www.newton.dep.anl.gov/natbltn/001-099/nb057.htm Forest Preserve District of Cook County]
* [http://www.oprf.com/divide/page2.html Oak Park - Ancient Lake Chicago & Continental Divide]
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