page_title: Lake Chicago
section_title: Chronology
hierarchical_section_title: Lake Chicago / Chronology
caption_attribution_description: English: Map of Glacial Lake Maumee, Saginaw, and Chicago, based on the USGS Report of 1915
context_page_description: Lake Chicago was a prehistoric proglacial lake that is the ancestor of what is now known as Lake Michigan, one of North America's five Great Lakes. Fed by retreating glaciers, it drained south through the Chicago Outlet River.
context_section_description: 13,000 to 11,000 years before present
  The earliest formation of Lake Chicago occurred when the Michigan Lobe of the glacier retreated northward into the basin of modern Lake Michigan, ca 13,000 years ago.  The edge of the retreating glacier formed moraines, the Park Moraine in present-day Illinois and the Lake Borders Moraine in Indiana and Michigan.
  The ice continued northward forming the next phase of Lake Chicago.  The lake level remained at 640' above sea level, but the ice margin was a third of the way north, opening a channel across Michigan, draining the Lake Saginaw and Lake Whittlesey proglacial lakes in the Lake Huron and Lake Erie basins.
  When the ice retreated northward enough to open the Mohawk River valley, the waters in the Lake Huron and Lake Erie basin diverted from the Michigan outlet, leaving Lake Chicago as a headwaters lake.  Continued northward migration of the glacier, set the stage for the next major proglacial lakes in the Lake Michigan basin as Lake Algonquin and then Nipissing Great Lakes.
caption: Early Lake Chicago at the edge of the ice sheet
exif: {}