When and how was Lake Michigan formed?

The last pull-back from the highland area created a lake between the retreating ice and the moraines. Essentially, the moraines acted as a dam at the southern tip of Lake Michigan that water could pond behind. read more

Lake level was high in Lake Michigan about 1,700 years ago. This high stage caused erosion of the east and west margins of the lake. By 1,500 years ago, the sediment eroded from the western margin of the lake had formed a sand spit that extended off of the bedrock highland in Illinois and reattached farther south in Indiana (see third image in the diagram above). read more

Lake Chippewa was a lower lake stage of Lake Michigan, created when the retreating ice sheet uncovered the St. Lawrence Seaway, a sea level outlet. It was the result of significantly lower lake levels, referred to as the Chippewa low levels. read more

Lake Michigan is the lake that divides Wisconsin and Michigan. It is also the lake that the city of Chicago lays on. read more