Mysterious Craters Discovered on the Bottom of Lake Michigan Could Hold Lessons About Early Life on Earth

The Great Lakes are full of mysterious clues about the past, from prehistoric hunting blinds to a Stonehenge-like arrangement of granite blocks.

Now, researchers have made yet another puzzling discovery deep beneath the surface of Lake Michigan: large, circular craters.

In 2022, a team of researchers with the National Oceanic and Atmospheric Administration (NOAA) set sail on Lake Michigan to map the Wisconsin Shipwreck Coast National Marine Sanctuary, a federally designated area that protects at least 36 shipwrecks.

During that expedition, they were surprised to find massive depressions dotting the lakebed. Around the same time, shipwreck hunters Brendon Baillod and Dusty Klifman also noticed the craters.

In late August, researchers returned to the marine sanctuary to take a closer look using a remotely operated underwater vehicle. They found roughly 40 depressions ranging from about 300 to 600 feet across, reports the Milwaukee Journal Sentinel’s Caitlin Looby. The craters are located roughly 14 miles southeast of Sheboygan, Wisconsin, some 450 feet below the surface of the lake. They’re roughly laid out in a line.

“How did they form? Why are they there, specifically in the bedrock?” Kevin Cullen, executive director of the Wisconsin Maritime Museum, says to NBC26 WGBA-TV’s Preston Stober. “We’re all scratching our heads wondering what could these things be.”

While scientists don’t know what created the depressions, one possible explanation is that they are sinkholes that formed as groundwater flowed beneath the lake’s limestone bedrock. If that were true, the groundwater may have eroded some of the limestone, causing caverns to form. Eventually, the caverns’ ceilings might have collapsed, making the large indentations on the lakebed.

Another possibility is that they were shaped by glaciers, per NBC 26. Or, the cavities could have formed “in the deep bottom sediment due either to water upwelling from below or trapped hydrocarbon offgassing,” Baillod tells Live Science’s Sascha Pare.

The depressions are dark, chilly and mostly devoid of oxygen, with temperatures that hover around 38 degrees Fahrenheit, per the Milwaukee Journal Sentinel. A handful of creatures can live in these conditions, including opossum shrimp, deepwater sculpin fish and the invasive quagga mussels that have disrupted the Great Lakes ecosystem.

Scientists suspect specially adapted bacteria may also live in the Lake Michigan craters, because they’ve found bacteria living in similar sinkholes at the bottom of Lake Huron. But they plan to investigate further to confirm.

For researchers, the Lake Michigan craters are more than just curiosities. They also offer a rare chance to explore extreme environments—like those found in Antarctica or in hydrothermal vents at the bottom of the ocean—without needing to travel far. What’s more, the indentations could provide additional insights about early microbial life on Earth, which thrived when oxygen wasn’t present.

“Right in our backyard, we have a window to the past, as well as to the deep sea,” says Bopi Biddanda, a microbial ecologist at Michigan’s Grand Valley State University, to WUWM’s Lina Tran.

Scientists have explored only about 15 percent of the bottom of the Great Lakes. An initiative called Lakebed 2030 hopes to change that, with a goal of creating a complete map of the Great Lakes by the end of this decade. As that work continues, researchers will likely make additional discoveries in these vast bodies of water.

“That’s the beauty of storytelling, the beauty of scientific inquiry,” Cullen says to NBC 26. “There’s always new stones to be uncovered.”

Sarah Kuta | READ MORE

Sarah Kuta is a writer and editor based in Longmont, Colorado. She covers history, science, travel, food and beverage, sustainability, economics and other topics.