In the shallow blue waters of the Bahamas, Belize and others people often remark upon the brightness of the water; lit by the light reflecting off of the white sand beneath. However one can find deviations from the shallow norm, underwater pits where the land drops away. Circular anomalies which suddenly drill deep down, these deeper spaces filled with darker, and decidedly chillier water. This is a ‘Blue Hole.’
Their entrances can be anything from 25 metres to 300 metres across; their darkness is a result of the depths absorbing the light. These peculiarities of the ocean reach up to, or rather down 202 metres, a lengthy vertical cave. The depth and narrowness of these vertical caves also limits their flow. At the base of the blue holes the water has lost all oxygen, making it inhospitable to anything more complex than bacteria.
The ‘Blue Holes’ are formed from a mixture of sea stands in previous ice ages and simple corrosion into the shore platform. These chemical reactions also allow Blue Holes inland, such as the Castalia Blue Hole in Ohio. Another part of Blue Hole formation is the halocline, where fresh and saltwater meet in a ‘Blue Hole’ – at this point corrosive reactions take place and eat into the sides, often producing quite long horizontal ‘arms’ of the hole up to 600m long.
These submerged vertical caves dot many shallow coastal platforms around the world, and when possible draw in thousands of tourists. All of whom are enraptured by the stark contrast to the surrounding water and their apparently ‘enigmatic, bottomless appearance.’ Humans, as they always have been, are enraptured by the mysteries of water, and that is why people love ‘Blue Holes’.