The Wired article about islands seen from space reminded me of another article I stumbled on. About what sounds like the reverse of what an island is. It took me a while of mucking around the Internet and my bookmarks but I finally found it, it was on my friend’s tumblr site: Blue Holes.
A Blue Hole is a submarine sinkhole or cave. They are steep-walled depressions, roughly circular, under sea level and get their names from the dark blue depths compared to the light blue shallows around them. Also called vertical caves, they are similar to cenotes, but underwater. (They are formed the same way, in limestone-rich terrain where chemical weather cause a cave roof to collapse in.)
One of the most breathtaking Blue Holes is the exquisitely circular Great Blue Hole in Belize, discovered and made famous by Jacques Cousteau, who declared it one of the top ten best dive sites in the world.
It is also believed to be the world’s largest Blue Hole and is part of the Belize Barrier Reef Reserve, a World Heritage Site. It’s a popular dive spot and a typical trip would take a full day with one dive in the Blue Hole, where you could see giant groupers, nurse sharks, reef sharks and maybe even the rare hammerhead, as well as the amazing stalactites and stalagmites that this spot is famous for.
Yes, Blue Holes are a thrill for divers, especially since many lead into caves or have spectacular cave formations. However, they are also incredibly dangerous, as many of them exceed permissible diving depths; the average diver is qualified to go to a depth around 30m, PADI recreational diving limit is 40m, and nitrogen narcosis begins to set in.
The most deadly of them is the Blue Hole located in the Red Sea. Because of the number of diving fatalities that have occurred there, this spot has earned the title “World’s Most Dangerous Dive Site”, as well as the nickname “Diver’s Cemetery”.
Accidents happen so frequently here because many divers try to find a tunnel through the reef wall known as “The Arch” that connects the Blue Hole to open water. However, this tunnel is hard to detect because of its odd angle, causing divers to descent too deep searching for it. The tunnel’s dept is at 52m, already a depth where divers could become narced.
Blue Holes are also dangerous because they are anoxic. Their water circulation is poor and beyond a certain depth, these conditions are unfavorable for marine life, but can support large numbers of bacteria.
The deepest Blue Hole is Dean’s Blue Hole, located in a bay on Long Island, Bahamas. It’s depth is an exceptional 202m; the next deepest Blue Hole is 110m.
Anyway, the article lists the Top 5 Amazing Blue Holes in the world. Read the whole thing here.
Tags: bahamas, belize, blue holes, diving, great blue hole, red sea
