A blue hole is a cave (inland) or underwater sinkhole. They are also called vertical caves. There are many different blue holes located around the world, typically in low-lying coastal regions. The best known examples can be found in Belize, the Bahamas, Guam, Australia (in the Great Barrier Reef), and Egypt (in the Red Sea).
Blue holes are roughly circular, steep-walled depressions, and so named for the dramatic contrast between the dark blue, deep waters of their depths and the lighter blue of the shallows around them. Their water circulation is poor, and they are commonly anoxic below a certain depth; this environment is unfavorable for most sea life, but nonetheless can support large numbers of bacteria. The deep blue color is caused by the high transparency of water and bright white carbonate sand. Blue light is the most enduring part of the spectrum; where other parts of the spectrum—red, yellow, and finally green—are absorbed during their path through water, blue light manages to reach the white sand and return back upon reflection.
The deepest blue hole in the world—at 202 metres (663 ft)—is Dean's Blue Hole, located in a bay west of Clarence Town on Long Island, Bahamas. Other blue holes are about half that depth at around 100–120 metres (330–390 ft). The diameter of the top entrance ranges typically from 25–35 metres (82–115 ft) (Dean's Blue Hole) to 300 metres (980 ft) (Great Blue Hole in Belize).
Read more about Blue Hole: Formation, Occurrence
Famous quotes containing the words blue and/or hole:
“When the inhabitants of some sequestered island first descry the “big canoe” of the European rolling through the blue waters towards their shores, they rush down to the beach in crowds, and with open arms stand ready to embrace the strangers. Fatal embrace! They fold to their bosoms the vipers whose sting is destined to poison all their joys; and the instinctive feeling of love within their breasts is soon converted into the bitterest hate.”
—Herman Melville (1819–1891)
“The more supple vagabond, too, is sure to appear on the least rumor of such a gathering, and the next day to disappear, and go into his hole like the seventeen-year locust, in an ever-shabby coat, though finer than the farmer’s best, yet never dressed.... He especially is the creature of the occasion. He empties both his pockets and his character into the stream, and swims in such a day. He dearly loves the social slush. There is no reserve of soberness in him.”
—Henry David Thoreau (1817–1862)