Natural paradises in danger to be saved: Great Blue Hole



by LORENZO CIOTTI

Natural paradises in danger to be saved: Great Blue Hole

The Great Blue Hole is a large underwater sinkhole, originally a limestone cave, which collapsed when sea level rose over 150,000 years ago. Increases in ocean acidification caused by the absorption of carbon dioxide in the atmosphere are damaging local marine life and coral reefs.

The Great Blue Hole is of great interest for scuba diving, even if due to the almost vertical walls (sometimes even overhanging walls) and the great depth, the lowest part of the cavity is little visited. The real attraction are the walls themselves, from about 30 meters deep, which are characterized by a very large number of stalactites, some up to 12 meters long.

Divers can swim among them, as long as they pay close attention to their buoyancy. The deeper the realm of technical diving begins, with narrower passages.

Natural paradises in danger to be saved: Great Blue Hole

It is located near the center of the Lighthouse Reef Atoll, about 60 km away from Belize City.

The cavity is almost perfectly circular, over 300 meters wide and 123 meters deep. Being part of the Belize Barrier Reef it is recognized by UNESCO as a World Heritage Site. It formed as a limestone cave during the last Ice Age when the sea level was much lower.

As the ocean began to rise, the cave flooded and the roof collapsed to the bottom, forming a submerged collapse valley. The Great Blue Hole is frequented by various marine species of which we report the most important, among the sharks we remember the nurse shark, the bull shark, the C.

perezi and finally the black tip reef shark. Among the other species with greater diffusion we remember the Epinephelus caninus known with the name of giant grouper. An expedition was conducted in the summer of 1997 to collect core samples from the Blue Hole's floor and document the cave system.

To accomplish these tasks, all of the divers had to be certified in cave diving and mixed gases. In December 2018, two submarines descended into the Blue Hole in an attempt to map its interior. Using sonar scanning, the team was nearly able to complete a 3-D map of the 1,000 foot wide hole.

One of their discoveries was a layer of hydrogen sulfide at a depth of approximately 300 feet (91 m). The water at that depth and below becomes dark, anoxic and devoid of life. The submarine expedition also discovered the bodies of two divers at the bottom, out of three believed to have gone missing while diving there.