• Location: 60 miles (100 kilometers) off the coast of Belize (Lighthouse Reef Atoll)
  • Diameter: 984 feet (300 meters)
  • Depth: 410 feet (125 meters)

Believed to be the largest underwater sinkhole in the world, the Great Blue Hole is a popular destination for divers. Lying at the center of the Lighthouse Reef Atoll, the sinkhole is thought to have originally been a limestone cave that formed some 150,000 years ago. When sea levels rose following the last glacial period, the cave collapsed and created the hole we see today (Foer, Thuras, & Morton, 2016, p. 420).

Glyn Collinson who recently dived the Great Blue Hole described it as:

It was the deepest, deep blue hole imaginable; A chasm that fell away deep into the deep, dark blue. It had been forged out of solid rock as caverns, hundreds of thousands of years ago during the last ice age. For eons, water filtered through the rock and into these great stone cathedrals, breeding multicolored stalactites and stalagmites. Then, one by one they collapsed in on each other, creating a chasm four hundred feet deep. As Earth’s swollen polar ice-caps receded, the warm Caribbean ocean swept in to fill the chasm with boiling white hands, the last rays of sunlight struck the chasm’s floor. Then, as the limestone broke down, it began to rain tiny fragments of rock, which slowly began to fill the great Blue Hole.

(Great Belize, n.d.)

Origin of the Belize Atolls

The Belize atolls are unique in that they did not form from subsided volcanoes. Instead, they were limestone ridges upon which coral grew. As sea levels rose after the last ice age the coral continued to grow and form the outer walls of the atolls with a shallow lagoon inside. The depths surrounding the atolls are often thousands of feet deep and the lagoons have an average depth of 10-30 feet (Great Belize, n.d.).

Spanish explorers charted the atolls in the 16th century. Surviving charts would appear to indicate that Lighthouse Atoll was originally called Quattro Cayas (four cayes) or Eastern Reef. English occupation a century later would later give it the name Lighthouse Reef after the establishment of a navigational aid on Half Moon Caye (Great Belize, n.d.).

In 1971, famous oceanographer Jacques Cousteau explored the hole and confirmed its limestone composition, noting that there are stalactites and stalagmites beneath the surface. He would declare it one of the top ten diving sites in the world (anhie, 2019).


As can be seen, the Great Blue Hole has been known for some time. This is not the only underwater sinkhole in the world, merely the biggest. I do not dive and I have no real interest in visiting this place. Although, it does look interesting. However, the idea of diving into a giant, dark, and deep hole in the ocean floor terrifies me! If a black hole just opened up on the bottom of the Caribbean Sea would you jump into it? I’ll pass thank you.


anhie. (2019). Great Blue Hole. Retrieved from

Foer, J., Thuras, D., & Morton, E. (2016). Atlas Obscura. New York, NY: Workman Publishing.

Great Belize Blue Hole. (n.d.). Retrieved from