Emily Chan
In 2022, researchers were working on a project to map the lakebed inside the Wisconsin Shipwreck Coast National Marine Sanctuary, a protected area of Lake Michigan that contains at least 36 shipwrecks.
Shockingly, only 15 percent of the bottom of the Great Lakes has been mapped in high resolution, but that’s sure to change in the coming years.
During the mission, sonar scans revealed strange circles at the bottom of Lake Michigan. Back then, scientists were unable to explain what the discovery was, but now, a survey of the shapes has revealed that they are huge craters.
According to Russ Green, a maritime archaeologist who was part of the project, the circles looked natural rather than artificial. They were most likely depressions in the lakebed, but the researchers weren’t completely sure.
“Any kind of discovery in the Great Lakes is exciting,” Green said. “But these features really stand out—they are in deeper water (500 feet) and weren’t known before, as far as we can tell.”
A local shipwreck hunter named Brendon Baillod spotted the circles around the same time as Green’s team. He thought the circles were craters that measured between 20 and 40 feet in depth.
After the data from the initial mapping expedition was processed, Green, Baillod, and colleagues reached out to scientists at the National Oceanic and Atmospheric Administration’s (NOAA) Great Lakes Environmental Research Laboratory (GLERL).
They conducted a survey to examine the circles further. They used a remotely operated vehicle to confirm that the shapes were giant natural craters. Overall, there were about 40 craters, but more may be found in the future.
The craters were on the lakebed roughly 14 miles southeast of Sheboygan, Wisconsin. They stretched southward in a line toward Port Washington, Wisconsin.
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