by 1 Cylivers
Blue holes are giant and sudden drops in underwater elevation that get their name from the dark and foreboding blue tone they exhibit when viewed from above in relationship to surrounding waters. They can be hundreds of feet deep and while divers are able to explore some of them they are largely devoid of oxygen that would support sea life due to poor water circulation - leaving them eerily empty. Some blue holes, however, contain ancient fossil remains that have been discovered, preserved in their depths.
Blue holes formed during past ice ages, when sea level was as much as 100-120 meters lower than at present. 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 Yucatan Peninsula, such as at the Great Blue Hole at Lighthouse Reef Atoll, Belize.
The deepest blue hole in the world is Dean's Blue Hole at 663ft. The next deepest holes are only around 350-400 feet deep
