Glaciers / Glacial Features

The landforms of the Sleeping Bear Dunes National Lakeshore are very young. Until only 14,000 years ago, what we know as northern Michigan was covered with ice. Over the course of the last two million years, glaciers covered and moved through the area many times. No one knows exactly how thick the glaciers were, but it is estimated that at the Sleeping Bear Dunes they were about 1,200 feet (350 meters) thick. The ice was so heavy that it pushed down the earth’s surface.

As these glaciers moved, they sculpted the land, gouging out what would become lakes, and depositing rocks, gravel, sand, and clay to form hills. Features like Pyramid Point, Sleeping Bear Plateau, and Empire Bluffs guided the more recent glaciers into places like Good Harbor, Glen Lake, and Platte Bay. Sometimes, huge ice blocks broke off from the retreating glaciers and became covered by gravel, sand, and other debris. When these ice blocks melted, they left behind large, cone-shaped depressions called kettles. The landform features we see in the park today are the result of the last glaciers which retreated approximately 11,800 years ago.

As the glaciers melted, the Great Lakes basins that were carved by the glaciers filled with water. The ice in Sleeping Bear Bay melted quickly but couldn’t flow north due to remaining ice. Instead, a temporary river carried the meltwater south from what is now Glen Lake, along the route of M-22, around Empire, and into the Platte Bay. One can see this old glacial drainage channel, now dry, where it crosses M-22 at Stormer Road. The size of this feature shows how much meltwater once flowed.

Over the past 11,000 years, waves from what is now Lake Michigan have worn down the moraine headlands, turning them into the large bluffs one sees today. This created the steep sand and gravel faces at Empire Bluff, Sleeping Bear Bluffs, and Pyramid Point. This process is ongoing, especially during periods of high-water levels in Lake Michigan.

There are several embayment lakes in the National Lakeshore. North Bar and South Bar Lakes near Empire, as well as the Glen Lakes and the Platte Lakes, used to be part of the larger Great Lake (now called Lake Michigan). These embayment lakes were separated from the larger lake by sand that was moved along the shoreline as the lake level dropped. This process continues along the Lake Michigan shoreline today. The prevailing southwest winds create waves that push sand northward, little by little. During storms, larger amounts of sand are moved in the same way, wave after wave.

Some of the most striking features in the park today are the perched dunes. These dunes are sitting on top of (already tall) glacial moraines. As wind and Lake Michigan waves erode the headlands, the wind blows the sand up onto the moraines where they form Perched Dunes. Larger and heavier stones roll down toward the beach, while lighter and finer clay material is dispersed by the wind. This ongoing process is observable from the Lake Michigan overlook on Pierce Stocking Scenic Drive.