Blue holes in the ocean?

Most of you may have heard of or read about black holes in space, but are you aware of the existence of something called blue holes in the ocean? Most probably not.

However, ocean blue holes do exist and they are considered to be unique and also one of the most fascinating natural environments in the world. So, let’s take a dive into these deep blue holes to find out more about them.

What exactly are blue holes?

Blue holes, also known as submarine caves, vertical caves or sinkholes, are roughly circular subterranean caves or steep walled depressions(hollows on the surface).

They are a phenomenon (remarkable thing) created during the ice ages when sea levels were much lower - about 100-200 mt lower than at present. They are actually limestone cave formations which have been subjected to the same chemical weathering common to all limestone-rich terrain.

At the end of the ice age, the roofs of many of these caves collapsed with the weight of the water and they were filled with water. Today these submerged caves and cavities are known as blue holes; there are inland blue holes (found on land) and marine or ocean blue holes.

Why are they known as blue holes?

The drastic contrast between the dark blue coloured water (due to the depths of the holes) and the lighter blue water of the shallow area around them, has led to these deep, roughly circular and steep depressions to be called blue holes.

Where can they be found?

Typically found on shallow carbonate platforms they can be found mostly around the Bahama Bank and Mexico’s Yucatan Peninsula, such as the Lighthouse Reef Atoll-Belize located in the Caribbean.

All the main islands of the Bahamas have blue holes.

The largest island of Bahamas, Andros Island has 178 on land and 50 in the sea. They can be described as entrances to the cave systems which run under the island and sea floor. The Bahamas blue holes are considered to be some of the best natural laboratories to study the geological past as many of them are pristine (unspoilt) and unique.

The Bahamas archipelago consists of a chain of islands and shallow water ‘banks’ which stretch from north east to south west, extending some 1400 km from Florida to the Island of Hispaniola.

The entire region had been considerably affected by sea level changes during the Pleistocene Ice Age.

In fact, as a result, Bahamas has the only known tidal blue holes in the world. Affected by the ocean tides, these blue holes blow out and suck in water. Cold, subterranian water which may be milky with hydrogen sulphide and algae is pumped out while water which is crystal clear from surrounding sea water is sucked in.

What are they like and how deep are they?

The deepest blue hole in the world is called the Dean’s Blue Hole and is about 663ft in depth. Most other blue holes average a depth between 360 and 400 ft.

The Great Blue Hole, which is near the centre of Lighthouse Reef - a small atoll 60 miles from the mainland Belize City - is circular in shape. It is over 1,000 ft across and about 400 ft in depth. There are other blue holes - the Blue Hole of Castalia (U.S) is one. It is an inland blue hole.

The Great Blue Hole of Belize is considered to be one of the most astounding diving sites in the world, like most of the other blue holes.

Even though blue holes are not favourable environments for most sea life, a large number of bacteria and other species are found in blue holes. Most of these depressions are so awesome to look at that they have become a divers; paradise today.

In fact, it is said that Jacques Cousteau pioneered a route into the Great Blue Hole, in his famous research ship Calypso in 1972 and this route is now used by the diving trade. He declared it as one of the ten best sites in the world for scuba diving.

Continued next week