Blue hole
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The term blue hole is usually used to refer to a submarine cave or sinkhole; in some scientific circles however, these are more specifically called "black holes", or "vertical caves".[1]
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[edit] Description
As used informally, they are often 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.[2] 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.[3]
[edit] Formation and Location
Blue holes formed during past ice ages, when sea level was as much as 100-120 meters lower than at present.[4] At those times, these formations were subjected to the same chemical weathering common in all limestone-rich terrains; this ended once they were submerged at the end of the ice age.
Blue holes are typically found on shallow carbonate platforms, exemplified by the Bahama Banks, as well as on and around the Yucatán Peninsula, such as at the Great Blue Hole at Lighthouse Reef Atoll, Belize.
