Two years ago, sonar images revealed strange circles at the bottom of Lake Michigan that puzzled scientists. Recent surveys have determined these shapes are giant holes, but researchers believe many secrets remain to be uncovered.
Discovery of the Holes
The holes were first identified in 2022 during a mission to map the lakebed within the Wisconsin Shipwreck Coast National Marine Sanctuary. This protected area contains 36 known shipwrecks, with the potential for many more undiscovered wrecks. The sonar mapping revealed unusual circles that appeared natural rather than human-made. According to Russ Green, a maritime archaeologist and superintendent of the sanctuary, these shapes were likely depressions in the lakebed, but their true nature was uncertain.
Expert Insights
Green expressed excitement about the discovery, stating, “Any kind of new discovery in the Great Lakes is exciting. But these features really stand out—they are in deeper water (about 500 feet or 150 meters) and weren’t known before, as far as we can tell.”
Brendon Baillod, a local shipwreck hunter, also observed these mysterious circles while searching for a sunken freighter. He described the shapes as craters measuring between 20 and 40 feet (6 to 12 meters) deep, with many in their search grid being between 500 to 1,000 feet (150 to 300 meters) in diameter and of irregular shapes.
Follow-Up Research
Although there was a delay in processing the data from the initial mapping expedition, Green and Baillod collaborated with scientists from the National Oceanic and Atmospheric Administration’s (NOAA) Great Lakes Environmental Research Laboratory (GLERL).
Joint Survey
In August 2023, the research teams conducted a joint survey using a remotely operated vehicle to investigate the circles more closely. They confirmed that the shapes are large, naturally occurring craters. Approximately 40 were counted, with more anticipated to be discovered. Steve Ruberg, a researcher at GLERL, described the craters as “perfect, little circles” located about 14 miles (23 kilometers) southeast of Sheboygan, Wisconsin, and aligned towards Port Washington.
Comparison with Lake Huron
Researchers had previously found similar depressions at the bottom of Lake Huron, located between Michigan and Canada. Those depressions were identified as sinkholes, which occur when groundwater dissolves the underlying bedrock, causing the surface layer to collapse. Given that Lake Michigan partially sits on limestone, which is susceptible to dissolution, it is likely that the craters in Lake Michigan are also sinkholes.
Ongoing Investigations
While some researchers are hesitant to label the circles as sinkholes without further research, Baillod proposed they might more accurately be described as craters formed by water upwelling or trapped hydrocarbon offgassing.
The recent survey revealed no signs of water escaping from the holes, which would indicate groundwater circulation beneath the lakebed. However, Ruberg anticipates that researchers will eventually detect some groundwater activity. The images and videos captured during the survey showed freshwater shrimp, small fish, and invasive quagga mussels inhabiting the holes.
Future Research and Impact
The potential impact of these holes on Lake Michigan remains uncertain, but researchers are optimistic about uncovering more information. Green stated, “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.”
Multiple-Choice Questions (MCQs):
- What did the sonar images revealed two years ago at the bottom of Lake Michigan?
- A) Shipwrecks
- B) Strange circles
- C) Ice formations
- D) Geological surveys
Answer: B) Strange circles
- In what year were the holes in Lake Michigan first discovered?
- A) 2020
- B) 2021
- C) 2022
- D) 2023
Answer: C) 2022
- What did the recent survey confirm about the shapes found in Lake Michigan?
- A) They are man-made
- B) They are large, naturally occurring craters
- C) They are shipwrecks
- D) They are ice caves
Answer: B) They are large, naturally occurring craters
- What feature of Lake Huron was found to be similar to the depressions in Lake Michigan?
- A) Icebergs
- B) Shipwrecks
- C) Sinkholes
- D) Coral reefs
Answer: C) Sinkholes
- What did researchers find inhabiting the holes during their investigation?
- A) Coral
- B) Freshwater shrimp, small fish, and invasive quagga mussels
- C) Sea turtles
- D) Algae
Answer: B) Freshwater shrimp, small fish, and invasive quagga mussels