Located in Belize, the Great Blue Hole is the world’s largest sinkhole, measuring 300 meters (984 feet) across and 125 meters (410 feet) deep into the Earth’s crust. Scuba divers and snorkelers have been exploring the surface waters for decades, but few have dared to venture deeper beyond the depths.
A Glimpse into the Bottom of the World’s Largest Sinkhole, the Great Blue Hole
In the winter of 2018, a crew from Aquatica Submarines started their descent to the bottom of the Great Blue Hole. The team included Fabien Cousteau, grandson of underwater explorer Jacques Cousteau, who put the Great Blue Hole on the map back in 1971. The group’s mission was to create a 3-D map of the Great Blue Hole’s interior, but along the way, they came across some common and not-so-common sights.
Marine life and then darkness
They found the usual reef sharks, turtles, and giant corals. But as they pushed for 90 meters more, life started to vanish. “One of the crazy things about the hole is the hydrogen sulfide layer,” says Erika Bergman, chief pilot, oceanographer, and operations manager.
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The thick layer of toxic hydrogen sulfide spans the width of the entire Great Blue Hole like a floating blanket. The layer descends at roughly 300 feet, cutting out all light and life, plunging divers into darkness. “You lose all of that Caribbean sunlight and it just turns completely black, and it’s totally anoxic down there with absolutely no life,” explains Bergman. “Down there, we found conchs and conch shells and hermit crabs that had fallen into the hole and suffocated, really.”
Thanks to their high-resolution sonar, Bergman and her team were able to see the Great Blue Hole’s features in stark detail. One of the most exciting findings was never-before-seen stalactites, a type of mineral formation shaped like icicles, roughly 407 feet into the Great Blue Hole, very near the bottom. “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 says.
It is to be noted that stalactites can only form because water is dripping down stone. “And so we know that this was a big, dry cave, and it was during a really prolific era on Earth, so there were probably lots of stuff living in it.”
Scientists think this cave was formed during the last Ice Age, which ended about 14,000 years ago. That was when sea levels began to rise and the cave flooded and collapsed, leaving behind the Great Blue Hole we see today. Researchers think that other marine sinkholes, like Dragon Hole in the South China Sea and Dean’s Blue Hole in the Bahamas, probably formed the same way.
A Coke, a GoPro, and human remains
As the team continued to explore the bottom of the hole, the team was also pleased to see that the Great Blue Hole was pretty free from trash. “There were basically two or three little pieces of plastic, and other than that, it was really, really clear,” says Bergman.
They found a 2-liter Coke bottle and a lost GoPro containing vacation photos. But that wasn’t all. The team encountered two of the probable three people who have been lost in the Great Blue Hole. “So we found kind of the resting place of a couple folks, and we just sort of very respectfully let the Belize government know where we found them, and everyone decided that we would just not attempt any recovery. It’s very dark and peaceful down there, just kind of let them stay.”
Intriguingly, not everything the team found could be identified. They found some unidentifiable tracks at the bottom of the Great Blue Hole. Bergman says these remain “open to interpretation.” Scientists predict this hole won’t be around forever to explore. Every day, waterfalls of sand fall into it, slowly filling it up like an underwater hourglass. But as for now, we can still admire its beauty and study its many mysteries.