Michigan’s Little Finger has been getting a lot of national media attention for the fantastic ice caves that have formed off the Leelanau Peninsula, but it’s a good time to check out the Thumb as well! Turnip Rock is on private property and reachable in the summer only by boat. In wintertime, however, walking on publicly owned Lake Huron becomes an option.
The Point Aux Barques – Turnip Rock geocache explains:
Everyone that received their grade school education in Michigan learned that glaciers pushed their way over Michigan several times. The result is glacial drift averaging 200 to 300 feet deep covering on top of the bedrock. The thickness of drift has measured over 1,000 feet in a few Michigan locations. Rarely can we see exposed bedrock that has been sculptured by non glacier forces. This is one of the locations in southern Michigan where the sandstone bedrock is exposed at the surface. The amount of shoreline that has exposed sandstone is about one mile, but a lot of beauty has been sculptured in the stone.
The locals call the main structure here “Turnip Rock”, because of it’s shape. Geologists call it a “Sea Stack”. A definition of a sea stack is an isolated pillar-like rocky island or mass near a cliff shore, detached from a headland by wave erosion assisted by weathering. Waves force air and small pieces of rock into small cracks, future opening them. The cracks then gradually get larger and turn into a small cave. When the cave wears through the headland, an arch forms. Further erosion causes the arch to collapse. This causes a pillar of hard rock standing away from the coast. Generally occurring in sedimentary rocks, sea stacks can occur in any rock type.
Here’s a map to Turnip Rock.