Mystery tracks have been discovered at the bottom of the Great Blue Hole—the world’s biggest ocean sinkhole, which sits about 60 miles from the coast of Belize.
In December last year, a team of explorers, including billionaire Richard Branson and Fabien Cousteau, the grandson of French explorer Jacques Cousteau, took part in a mission to dive to the bottom of the hole to find out what was down there. At over 1,000 feet wide and 410 feet deep, it is a largely unexplored natural wonder.
It formed as a limestone cave hundreds of thousands of years ago when the sea level was far lower. At the end of the last ice age, ice caps melted and sea levels rose, submerging the cave to become what is now the Great Blue Hole.
In November and December last year, teams conducted over 20 dives into the void in order to create a 3D map of it. One of these dives was broadcast live on the Discovery Channel. In it, Branson and Cousteau, led by submarine pilot Erika Bergman, ventured into the hole’s depths.
In an interview with CNN Travel, Bergman has spoken about what she saw inside the Great Blue Hole. She said they found never-before-seen stalactites at the base of the hole: “That was pretty exciting because they haven’t been mapped there before. They haven’t been discovered there before.”
Even though the water was completely dark, high-resolution sonar equipment on board allowed them to see hidden features of the formation. “You can be 20 or 30 meters away from a stalactite or a hunk of the wall and see it in every perfect detail, better than eyesight could even provide,” she said.
They also found some unidentifiable tracks right at the base of the hole—the source of which are “open to interpretation,” Bergman said.
Researchers are now close to completing the 3D sonar map of the hole. “It looks really cool—it’s this mesh-layered, sonar scan of the entire thousand-foot diameter hole,” Bergman told CNN.
A blog post by Aquatica Submarines, which was involved in the expedition, said: “The view the map provides is enhanced with other passive submarine-collected environmental data from the Blue Hole. Once processed and collated, this data will be shared with the Government of Belize and the larger global scientific community as a legacy from the expedition.”
As well as mystery tracks, Branson recently said, they found plastic bottles sitting at the bottom of the Great Blue Hole. In a blog post about the dive, he wrote: “As for the mythical monsters of the deep? Well, the real monsters facing the ocean are climate change—and plastic. Sadly, we saw plastic bottles at the bottom of the hole, which is a real scourge of the ocean. We’ve all got to get rid of single-use plastic.”
A documentary about the dive, by INE Entertainment, is due to be released this spring.