Michigan

A few years back, scientists noticed strange circles at the bottom of Lake Michigan. This was when they mapped the lakebed inside the Wisconsin Shipwreck Coast National Marine Sanctuary in 2022. 

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Now, two years later, they finally have an explanation for these circles. Researchers say that these circles are nothing but giant holes. 

Russ Green, a maritime archaeologist and superintendent of the sanctuary who took part in the expedition, told Live Science that they saw circles on the map that looked like natural occurrences. They appeared to be depressions in the seabed, but there was no confirmation.

Brendon Baillod, a local shipwreck hunter, also spotted the circles and was almost sure that they were craters, measuring between 20 and 40 feet (6 to 12 m) deep. He told Live Science, "There were dozens of them in our search grid."

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They reached out to scientists at the National Oceanic and Atmospheric Administration's (NOAA) Great Lakes Environmental Research Laboratory (GLERL) who examined the circles in a joint mission.

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A remotely operated vehicle was sent into the sea to study the circles, and it was confirmed that they are enormous, naturally occurring craters. Scientists say they saw around 40 of them, but there might be more of them, Steve Ruberg, a researcher at GLERL, told the Milwaukee Journal Sentinel.

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Earlier, similar depressions have been found at the bottom of Lake Huron bordering Michigan and Canada. These circles turned out to be sinkholes. These occur when the surface layer collapses because of groundwater dissolving the bedrock from below.

Ruberg believes that the craters in Lake Michigan might also be sinkholes since it sits partly on limestone, which is prone to dissolution. 

However, not everyone is of the view that the craters are sinkholes. "I think they might be more accurately called craters, which have formed in the deep bottom sediment due either to water upwelling from below or trapped hydrocarbon off-gassing," Baillod said.

As of now, no water has been found escaping from the holes. This means there is groundwater circulating beneath the lakebed. Ruberg still expects researchers will eventually detect some.  

Green said more research will be conducted to determine what the craters really are and the impact they might be having on Lake Michigan.