by Hannah Ettema
Everyone does it.
Person A: “What city are you from?”
Person B: [holds up hand and points to location of town.]
Has anyone from Michigan not used their hand to pinpoint their hometown? This is so normal for any Michigander to do. Using hands as maps is a part of Michigan culture.
How exactly are we so lucky to have our state shaped like a mitten? If you were thinking glaciers, you’re absolutely right.
MNA trustee and geologist Mary Ann Czechowski shed some light on Michigan’s glacial history in a recent interview. Mary Ann is a geology consultant and the author of Gold in Michigan.
A glacier is essentially a large river of ice that flows through a landscape.
Johns Hopkins and Gilman Glaciers in Glacier Bay National Park and Preserve
Today, glaciers can be found on every continent except Australia.
There have been four Ice Ages in the Earth’s history. In the last Ice Age, the Pleistocene Epoch began and lasted from approximately two million years to 12,000 years ago. During this time, warm and cool temperatures alternated and glaciers retreated and advanced in interglacial periods. Around the world, glaciers carved and influenced much of today’s landscape, including the Great Lakes and the state of Michigan.
Like bodies of water, the first glaciers flowed south from what is now Canada seeking the areas of least resistance. It is believed that the Great Lakes were once ancient riverbeds, providing the glaciers perfect pathways south.
With each advance and retreat of the glaciers, the shape and water level of the lakes changed. These changes weren’t happening in a matter of months, but over thousands of years.
Manistique Dune and Swale Nature Sanctuary with prehistoric beaches. Photo: Keith Sayor.
As the shape and water level of the lakes changed, the beaches did as well. When water from the glaciers retreated, it left behind a beach. The Manistique Dune and Swale Nature Sanctuary, recently visited on MNA’s fall adventure, has excellent evidence of these prehistoric beaches. In the sanctuary, a swell of sand will appear out of place among the trees but as you continue to walk towards the current water’s edge, you will walk through various sand swells among trees representing past water levels of Lake Michigan.
Evidence of glacial beaches can also be found at Frink’s Pond and Carl E. McAlvay Memorial Plant Preserves. See the MNA’s sanctuary page for more information on these sanctuaries and others throughout the state.
Many of Michigan’s inland lakes, including Walled Lake and Higgins Lake, were also formed by glaciers. These lakes are called kettle lakes, and were created when chunks of ice would break off the glacier and become embedded in the ground. When the ice chunk would melt, a kettle hole would be left and be filled by water from natural sources.
Goose Creek Crasslands Prairie Nature Sanctuary. Photo: Matt Schultz.
As the glaciers carved the landscape, they left deposits of sediment. Small pieces of rock originally from Canada have been found as far south as in Indiana and Ohio. Here in Michigan the Goose Creek Grasslands Prairie Nature Sanctuary rests in a glacial trough where raw gravel was left by retreating glaciers. Timberland Swamp Sanctuary is a basin that was formed by debris left by the glacier.
Saginaw Wetland Nature Sanctuary. Photo: Meghan Good.
Michigan sits atop bedrock composed of many rock types, including sandstone. As the glaciers eroded the landscape of Michigan, sand became much more prevalent, giving us our sandy beaches, sand dunes and wetlands. The sand blocks the drain of water from land into the lakes, and trapped water creates wetlands, such as the Saginaw Wetland Nature Sanctuary in Huron County.
The sand eroded by the glaciers has also shaped Michigan’s shorelines today. Michigan receives mainly westerly winds, causing the Lake Michigan coastline to have significant dunes not only along the shoreline, but also further inland than usual.
Sleeping Bear Dunes
Lake Huron on the other hand, has fewer dunes due to the fact that the westerly winds blow the sand back into the lake, making for a sandy bottom. Redwyn’s Dunes Nature Sanctuary on the shore of Lake Superior has the only sand dunes on the Keweenaw Peninsula, which were blown in after the glacial retreat
For more information volunteering or visiting sanctuaries, please visit the MNA website . Special thanks to our members for their support and help throughout Michigan.