From:
http://www.panoramio.com/user/68388
Dean's Bluehole off Long Island in the Bahamas is a pretty incredible place. The surface of the sinkhole starts at a depth of 18 ft. and descends to 663 ft. The average diameter is 250 ft. Tidal activity creates mild upward and downward currents. A tech diver made the bottom all the way to 663 ft. in 1992! More at:
http://www.stellamarisdiving.com/blueholefacts.html
Note the approximate 60 ft. orifice at 30 ft. deep is substantially smaller in diameter than the rough 250 diameter shaft. It can be a trip descending under negative rock slopes into narcotic depths on compressed air, disorienting to say the least but interesting all the same.
From:
http://www.verticalblue.net/
A video clip of the blue hole both above and below the water appears at:
http://tinyurl.com/37ujfw
The area of the blue hole
In "Morphometry and hydrology of Dean's Blue Hole, Long Island" by
Wilson, W L, Bahamas Journal of Science. Vol. 2, no. 1, pp. 10-14. 1994
"Dean's Blue Hole is an exceptional, world-class, karst feature for several reasons: it is the deepest known blue hole in the world (-663 feet) and is 62% deeper than any other explored cave in the Bahama Islands; the underwater room beneath the entrance shaft is the second largest known underwater cave room and may be the ninth largest cave room in the world; and the volume of water displaced during a tidal cycle indicates that significant cave passages may connect to the blue hole. Simply finding the cavernous passages that may connect to Dean's Blue Hole may be a daunting task because of the size and depth of the room. Elongation of large collapse rooms usually occurs parallel to horizontal passages. Based on the apparent elongation of the room in the east-west orientation, it seems reasonable to suggest that these ends of the room should be examined first. Deep Breathing Systems would be happy to assist other researchers who have an interest in studying Dean's Blue Hole."
More about Bahamian Blue Holes, geology and more at:
http://www.blueholes.org/pubpdf/symposia.pdf
You can checkout a 360 degree panoramic image of the blue hole at:
http://www.bahamas.com/bahamas/biih/index.aspx
From:
http://www.geocities.com/regkit/
A video clip of a Timo, a freediver heading into the bluehole using a monofin appears below. Sorry for all the tarpon footage, I suspect the videographer hasn't seen that many before. I can recall a large blind one in Warm Mineral Springs, an early man UW archaeological site years back. The sulfur content of the water destroyed diving gear and vision in aquatic life. Now that is a sight to ease out of the dark towards you. There was also a blind alligator too!
Long Island and the bluehole came up in a thread about "Bahamas Week At the FKA!" There is still more good stuff about the Bahamas and sinks at:
http://fksa.org/showthread.php?t=4167
From:
http://en.wikipedia.org/wiki/Dean's_Blue_Hole
.