What is a Blue Hole?

For some divers, the blue hole is an obsession. It's the legendary abyss often situated in the crystal blue waters of the Caribbean.

Nature fashioned these so-called blue holes, which are actually natural sinkholes, generally carved out of limestone. These sinkhole vertical caves were formed when sea level was much lower. Later, when water levels rose the holes were filled with water, adding the blue to the hole.

These holes can be seemingly bottomless to a scuba diver. Underwater we are really very limited as to how deep we can go. Although there are special sub-type contraptions that we can ride to the depths, diving with just a scuba tank is limiting. 1,000 feet, or 308 meters deep is about the upper limit to how deep wet suited divers can go.

Fresh water blue holes are an ideal place to deep dive because they're more contained than open water.

In the ocean, perhaps one of the most famous blues holes is the Blue Hole Belize, which was thrust into the public eye by Jacques Cousteau, who declared it one of the top scuba sites in the world. From the air it certainly looks impressive at 1,000 feet across, a navy blue set against the clear water. It's not the deepest blue hole in the world at 400 feet deep, but it's still an impressive site.

When Cousteau's team charted the hole they discovered its origins, which apparently is common to most blue holes. The Karst topography indicated that this was a dry land cave/hole, formed at first as a giant sinkhole caused by water erosion and layers of limestone. The team even recovered stalactites which were situated at odd angles, meaning that there were major shifts after the hole was formed.

Jon Bennett set the record for the deepest dive in one such blue hole off of Puerto Galera on the island of Mindoro in the Philippines. He dove to 1,000 feet. It took him over nine hours to make the trip down and back up again, because of decompression issues.

Besides being a haven for divers, blue holes also offer unique and very specific environments for sea life. They also serve as a record for underwater fossil hunters. Today, blue holes, especially in the Bahamas, are in danger.

A few of the companies which have now been in operation on Grand Bahama for as long as 30 years have been allowed to pollute, unchecked, the environment surrounding the industrial site, including the ground water which lies only, in many cases, three feet below the surface. The result of this activity has been that diving in the few caves, which are still in tact on the western side of Grand Bahama, is extremely dangerous due to the presence of toxic chemical waste. They are also dangerous because they are very unstable and made more so as a result of the blasting activity going on at the development site of the nearby container port facility.--http://www.blueholes.org/silent.html

Diving in some blue holes can be dangerous, as they can be choked with sewage, so if you're going to dive, do research on the cave beforehand by plugging the name into a search engine. If there are dangers you can find out about it that way, as well as by talking to experienced divers at the location. Don't get all your info from the dive team that's supposed to take you though!