Dean's Blue Hole
Dean's Blue Hole is the world's second deepest known salt water blue hole with an entrance below the sea level. It plunges 202 metres (663 ft) in a bay west of Clarence Town on Long Island, Bahamas.
A blue hole is a water-filled sinkhole with the entrance below the water level. They can be formed in different karst processes, for example, by rainwater soaking through fractures of limestone bedrock onto the watertable. Sea level here has changed: for example, during the glacial age during the epoch (ice age), some 15,000 years ago, sea level was considerably lower.
Dean's Blue Hole is roughly circular at the surface, with a diameter ranging from 25 to 35 metres (82–115 ft). After descending 20 metres (66 ft), the hole widens considerably into a cavern with a diameter of 100 metres (330 ft).
There are several fresh water sinkholes on land that are deeper than Dean's Blue Hole. The deepest one is Hranická propast in Hranice Karst in Czech republic. It is formed in devonian limestones, and polish speleodiver Krzysztof Starnawski reached here the record depth of 404 m (1,325 ft) on 27.9.2016. The other ones include the 270 m (890 ft) Boesmansgat in South Africa, Mexico's Zacatón at 335 m (1,099 ft) and the 392 m (1,286 ft) Pozzo del Merro in Italy.
The deepest known marine blue hole is Dragon Hole.
Coordinates: 23°6′23″N 75°0′31″W / 23.10639°N 75.00861°W
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