The movement of the Wisconsin Glacier has its left traces in the habitats and geological landmarks of the Southern Lake Michigan Rim (SLMR) over the course of thousands of years. The glacier made its furthest advance like a river of ice more than 15,000 years ago and retreated out of Indiana just over 13,000 years ago. The SLMR region is, geologically speaking, a young area, with older geological marks further south and newer geological areas closer to the Lake Michigan Shoreline.
The marks left by the Wisconsin Glacier on the lands in and around the SLMR region can be seen and studied today:
- After the glacier withdrew for the last time, Lake Algonquin (now Lake Michigan) began a series of advances and retreats, leaving distinct ridges such as the Glenwood Ridge.
- In Lake County, you can see the corduroy-like pattern of globally-rare beach ridges and wet swales that contain an amazing variety of life. These landforms are part of the dune and swale habitat that is bounded on the south by the Tolleston Ridge, the second oldest relic shoreline in the area.
- The movement of the glacier, and subsequent erosion by the wind and waves, led to the formation of the world-famous Indiana Dunes that span all three counties. This area contains a series of newer (foredunes) and older dune ridges, with Mt. Tom being one of the highest dunes in the Indiana Dunes State Park.
In addition to glacial movements, dynamic forces such as soil, wind, and water have created an amazingly diverse matrix of plant communities and habitats in the SLMR project area that exist nowhere else in the state. Due to thousands of years of climate changes, many of these biomes now overlap. An example of this is the colliding of the Tallgrass prairie habitat with eastern deciduous forests, creating unusual mixes of species such as jack pines, usually found further north, and prickly pear cacti, typically seen further south.
If you want to delve deeper into the geologic and glacial history of SLMR, consider reading the following sources:
- "How The Ice Age Shaped Indiana," a paper written by Jerry Wilson
- Overview of glaciation in Indiana by the Indiana Geological Survey
- "Calumet Beginnings" by Kenneth Schoon, Indiana University Press (November 12, 2013)