The deepest blue hole in the world lies just off the coast of Mexico and scientists have been left perplexed.
This underwater marine sinkhole is over 420 metres deep and explorers are still unable to reach its bottom, leaving a sense of mystery around the geological marvel.
Also known as Taam Ja’, which translates to ‘deep water’ in the Mayan language, the sink hole, which has low visibility from the surface, was discovered just over 20 years ago by a local diver.
In 2021, scientists tried to measure its depth with the help of an echo sounder to bounce soundwaves off the bottom of the hole.
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This only estimated a depth of 275 metres, but a 2023 expedition then found that it was at least 420 metres deep, though they were not sure if this was its bottom.
Experts used a device called a conductivity, temperature and depth (CTD) profiler, with its sensors measuring water pressure to determine its depth.
Just off the coast of Mexico’s Yucatán Peninsula, the sink hole has a number of geological and ecological features that are significant for marine biologists and other experts.
Blue holes are naturally occurring caverns on the sea floor with vertical walls, which are predominantly found in coastal regions.
This is due to the bedrock being made of soft types of rock, such as limestone, which can erode overtime and cause the rock to collapse.
Most sink holes are just tens of metres deep, though they can often link to underwater cave systems.
They aren't affected by ocean current, having poor water circulation and low oxygen levels deep down, making it hard for all life except microbes to thrive.
“While Taam Ja’ is the deepest known blue hole, another famous example is the Great Blue Hole in Belize. Many have been keen to explore blue holes over the years, with Richard Branson exploring the latter with Fabien Cousteau, the grandson of French explorer Jacques Cousteau, in 2018.
They ventured down in separate vessels, discovering a layer of hydrogen sulfide at around 91 metres, beyond which the water was dark and devoid of life.
When they made it to the perceived bottom, they even discovered rubbish and a two-litre plastic bottle, as well as a long-lost GoPro which contained photos from a holiday.
There were also two bodies found there, believed to be two explorers who went missing on a previous expedition.
Branson said on the Virgin website: "The Blue Hole is made of a complex system of caves that once formed on dry land. It is proof of how oceans can rise quickly and catastrophically.
"Sea levels were once hundreds of feet lower. 10,000 years ago the sea level rose by about 300 feet when a lot of ice melted around the world. At 300 feet down you could see the change in the rock where it used to be land and turned into sea."
Joshua Nair