The formations were confirmed to be large craters during a joint survey in August 2024. Researchers, including Green and colleagues from NOAA‘s Great Lakes Environmental Research Laboratory (GLERL), used a remotely operated vehicle to examine the site. They found around 40 craters, measuring between 500 to 1,000 feet in diameter, southeast of Sheboygan, Wisconsin.
Local shipwreck hunter Brendon Baillod noted these depressions while looking for a sunken freighter. He described them as irregularly shaped craters, some 20 to 40 feet deep. Baillod suggested trapped gas or water upwelling, rather than sinkholes, might be behind their formation.
Kevin Cullen from the Wisconsin Maritime Museum highlighted the geological mystery of these craters. He proposed they might be linked to underwater gorges formed by glaciers many years ago. Geologists suggested that the craters could be sinkholes as Lake Michigan sits partially on limestone, which can erode and form cavities. However, recent studies found no water escaping from these holes, indicating no groundwater movement yet.
Steve Ruberg from GLERL mentioned it is only a matter of time before water circulation beneath the lakebed is detected. The survey also captured life thriving in the craters, including freshwater shrimp, small fish, and invasive quagga mussels. Researchers aim to understand the role these formations play in Lake Michigan’s ecosystem.
While some information has been uncovered, many questions remain. Russ Green expressed excitement about future investigations, saying, “We’ll be exploring them for years to come to learn more, and sort out how they got there and what role they play in Lake Michigan’s ecosystem.” The craters stand as one of the Great Lakes’ intriguing geological mysteries, with more discoveries expected as research continues.