Many so-called Blue Holes began as karsts, a specific type of cave which forms when water soluble rocks such as limestone or dolomite erode and over the millennia. Sinkholes, cenotes, and dolines are all examples of karst formations found topside; some of these can also be found beneath the ocean’s surface and, in some cases, are actual caverns suitable for cave diving.
Blue Holes
There are many different blue holes around the world, many of which are notable dive sites. These sinkholes often appear perfectly circular from above, and beneath the surface, many feature spectacular vertical walls that lead to incredible depths. In some shallower blue holes, there are actual caverns and ledges to explore around the periphery, and at some locations, such as the Dahab Blue Hole in Egypt, passageways lead out into the open sea. Some of the most famous blue hole dive sites include:
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The Great Blue Hole in Belize near Ambergris Caye
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Dean’s Blue Hole off Long Island in the Bahamas, which is the deepest saltwater blue hole
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The Inland of Andros, in the Bahamas, where numerous reef and freshwater blue holes can be found
While many blue holes are deep, dark, and dangerous, with the Blue Hole at Dahab topping the list of the worlds' most dangerous dive sites, some are suitable even for newer divers to explore.
Cenotes
Deep natural pits which are often completely interconnected, the cenotes of the Yucatan Peninsula in Mexico and Central America were used as a source of fresh water by indigenous people, and were sometimes used for offering human sacrifices. They, like blue holes, were formed due to erosion; but in most cases, the water inside these amazing formations is quite shallow. Connected by underground rivers that flow for long distances, the insides of these formations often have high ceilings and in some cases are suitable for exploration even by those with very little cave diving experience. Often, getting to the cenotes to dive presents more of a problem than the diving itself does. Sometimes, divers have to hike long distances through buggy jungles, carrying tanks and full gear; and most of the time, entry and egress is accomplished via ladders that can be rickety. Despite the challenges involved with cenote diving, these beautiful sites are considered to be world class destinations, as their geology is fascinating and as the overall experience is completely otherworldly. Some notable cenotes include:
- Dos Ojos, located in Mexico’s Tulum
- Gran Cenote, also located in Tulum
- Bottomless Lakes, located near Roswell, New Mexico
Inside blue holes and cenotes, it is possible to experience haloclines, where fresh water mingles with salt water, and at many of these sites, visibility is absolutely incredible – in some cases, you’ll feel almost as though you are suspended in midair rather than diving in a body of water. At freshwater cenote sites, life is often limited, although it is not uncommon to encounter plants that grow in spots where sunlight penetrates, or to find yourself swimming past a colony of bats. In saltwater blue holes, though, the amount of marine life can be incredible. Next time you’re ready for an adventure, consider exploring one of these amazing geologic formations – you won’t be disappointed!