With a maximum depth of 925 feet, the wide waters of Lake Michigan have always held a sense of mystery and intrigue. Recent research expeditions have revealed a new, mysterious surprise: a series of huge craters scattered across the bottom of the lake, which were first spotted in 2022.
The craters were first discovered during a mission to map the bottom of a lake in the reserve, which has been the site of many shipwrecks. These peculiar circles appeared on the sonar images, hinting at natural formations, rather than something man-made.
"Any new discovery in the Great Lakes is exciting," said Russ Green, who led the mapping project. "But these features really stand out—they're at greater depth and haven't been known before, as far as we can tell."
Brendan Baylod, a dedicated shipwreck hunter, also noticed the circles while searching for a sunken freighter. He was convinced that the circles were craters.
"There were dozens of them in our search grid," Baylod said. "Most of them were 500 to 1000 feet in diameter and irregular in shape."
Hidden Craters in Lake Michigan
After processing the data from the initial mapping project, Green and Baylod turned to scientists at the National Oceanic and Atmospheric Administration's (NOAA) Great Lakes Environmental Research Laboratory (GLERL) for peer review.
The teams joined forces to further investigate the mysterious circles. In 2022, they conducted a detailed survey using a remotely operated vehicle, determining that each circle is a natural, huge crater. There are about 40 of them, and all craters extend south from a point southeast of Sheboygan, Wisconsin, toward Port Washington.
Steve Ruberg, a GLERL researcher, described the craters as "perfect, little circles" at the bottom of the lake. The team, however, believes there may be more craters in the depths of Lake Michigan.
Funnels or craters?
These formations bear a striking resemblance to sinkholes previously discovered at the bottom of Lake Huron, which borders Michigan and Canada.
Sinkholes are usually formed when groundwater dissolves bedrock, causing the top layer to collapse. Given the limestone base of Lake Michigan, which is prone to dissolution, the consensus is that these features are karst sinkholes. However, some researchers, such as Baylod, prefer the term "craters" until more empirical evidence is available.
"I think it would be more accurate to call them craters that formed in the deep bottom sediments, either by upwelling of water from below, or by release of trapped hydrocarbons," Baillod says.
A recent study found no signs of water leaking from the wells. This indicates that underground water circulates under the bottom of the lake.
The meaning of craters
Underwater life thrives in these craters, with small fish, freshwater shrimp and invasive quagga mussels "doing their thing in the dark," Ruberg says.
The exact effects of these craters on Lake Michigan and its ecosystem are not yet clear. Nevertheless, there is an atmosphere of anticipation and curiosity among researchers.
"We'll be studying them over the next few years to learn more and figure out how they got there and what role they play in the Lake Michigan ecosystem," Green said.
The meaning of Lake Michigan
Lake Michigan is the only Great Lake that lies entirely within the borders of the United States, and is a vital element of North America's ecological and cultural heritage. Spanning 22 square miles, it spans four states—Wisconsin, Illinois, Indiana, and Michigan—and nurtures a rich and complex ecosystem.
Native species such as lake trout and whitefish thrive here, while invasive quagga mussels challenge the lake's ecological balance. Formed by glaciers about 10 years ago, the lake's limestone basin tells the story of a dynamic geological past.
Future Great Lakes Research
Recent discoveries of Lake Michigan, particularly the large craters at its bottom, shed new light on its ancient formation and evolution and offer interesting clues about how this huge body of fresh water came to be. The importance of Lake Michigan is not limited to its geology. It serves as a lifeline for millions of people, supporting recreation, commerce and serving as an important source of fresh water.
The mysteries hidden in the depths of Lake Michigan highlight its dynamic and changing nature, and there is much more to be learned. In fact, of all five Great Lakes, only about 15 percent of the bottom has been mapped at high resolution. Scientists say we know more about the surface of Mars than the bottom of the Great Lakes.