If you travel off the coast of Belize, you’ll find an amazing natural phenomenon in the ocean: a giant sinkhole. It’s almost 1000 feet across and over 400 feet deep. At the bottom, there’s no light or oxygen. It’s easy to spot- the hole’s water is a dark blue, while the surrounding waters are much lighter. Advanced scuba divers explore at safe depths, while any snorkeler can experience the top of the hole. Known as the Great Blue Hole, it’s technically a vertical cave, lined with dried out coral. Because it’s so deep, it’s been the subject of curiosity for decades. In 1971, Jacques Cousteau filmed an episode of his TV show there. More recently, his grandson Fabien and a team traveled there, armed with much more advanced technology.
At the top of the sinkhole, the expedition was able to use more traditional tech because there was light. However, as they sunk deeper (led by oceanographer and chief submarine pilot Erika Bergman), they resorted to sonar heads and sound waves. This allowed them to create the first ever 3D sonar image of the famous sinkhole.
Certain features were especially interesting to experts. At around 130-160 feet deep, there are striking stalactite caverns. These formed 15,000 years ago when the sea level was much lower and the Great Blue Hole was a dry cave. Now, instead of the usual cave dwellers like bugs and bats, sea life swim these caverns. The expedition also found a stretch of the cave filled with dead conch who fell into the hole and couldn’t get back out. They died when they ran out of oxygen.
The team also discovered plastic trash at the bottom, showing just how extensive human activity is on our oceans. Even the darkness and stillness of the world’s second-largest ocean sinkhole isn’t safe from plastic pollution.