The Blue Hole's Deadliest Secret: Unveiling The Death Zone

The Great Blue Hole in Belize is the world's biggest ocean sinkhole, measuring 1,000 feet across and over 400 feet in depth. It formed thousands of years ago as a limestone cave and was submerged when sea levels rose at the end of the last ice age. The site has been a popular diving destination since the 1970s, but its internal structure and what lies at the very bottom remained a mystery—until recently.

In 2018, an expedition led by Erika Bergman, a National Geographic Explorer and submersible pilot for Aquatica Submarines, dived to the bottom of the chasm. They discovered a layer of hydrogen sulfide at a depth of 290 feet, below which there is no oxygen. This layer is so thick that it blocks out all light from above.

The team also found the bodies of two divers who had been lost in the hole, as well as evidence of previous attempts to escape. The discovery highlighted the dangers of diving in the Great Blue Hole, which has one of the highest diving fatality rates in the world.

Divers' bodies found at the bottom

The Great Blue Hole, a popular diving site off the coast of Belize, is the world's biggest ocean sinkhole. It measures 1,000 feet across and over 400 feet in depth. In December 2018, an expedition team including billionaire Richard Branson, Fabien Cousteau (grandson of explorer Jacques Cousteau), and oceanographer Erika Bergman, ventured into the Blue Hole to create a 3D map of its interior.

The team discovered a layer of hydrogen sulfide at a depth of 290-300 feet, below which there is no oxygen. This layer casts the rest of the hole into darkness. Erika Bergman described the experience of passing through the layer:

> "You lose all of that Caribbean sunlight and it just turns completely black."

Tragically, the team also discovered the bodies of two divers who had been lost in the hole. The divers were left undisturbed, with Bergman commenting:

> "We notified the local authorities, and everyone agreed to leave them undisturbed. They are at peace."

The discovery of the divers' bodies highlighted the dangers of the Blue Hole, which has claimed multiple lives due to its extreme depth and toxic, anoxic environment.

Hydrogen sulfide layer

The Great Blue Hole in Belize is a marine sinkhole inside the Lighthouse reef of Belize. It is the world's biggest ocean sinkhole, measuring 1,000 feet across and over 400 feet in depth.

One of its most interesting features is the hydrogen sulfide layer, which sits at a depth of around 90 to 300 feet. This layer is formed of hydrogen sulfide (H2S), a toxic, corrosive, colourless, flammable, and deadly gas that is dissolved in the water. While it is less concentrated in the Blue Hole than in its gaseous form, it is still potent enough to prevent sea life from passing through it.

The hydrogen sulfide layer is responsible for the absence of oxygen in the waters below. As Erika Bergman, Chief Pilot and Director of Operations of Aquatica, explains:

> "Anything that fell into the hole decomposed until that process used up all of the oxygen below 290 feet. That means that below the H2S, there's no oxygen and anything that falls down there now is preserved. Without oxygen, nothing survives."

This anoxic environment has created a "graveyard of shellfish" at around 350 feet, where thousands of creatures have swum too deep and perished.

The hydrogen sulfide layer also blocks out the light from above, creating a dark and eerie environment below. As Richard Branson, who joined an expedition to the Great Blue Hole, described:

> "We didn’t expect to see any creatures below. But when we got to the bottom we could see crabs, conches and other creatures that had fallen into the hole, arrived on the bottom and then ran out of oxygen and died."

Death by nitrogen narcosis

Nitrogen narcosis, also known as depth intoxication or rapture of the deep, is a change in consciousness and neuromuscular function caused by breathing compressed inert gas. It is a reversible alteration in consciousness that occurs while diving at depth. The effects are similar to those of alcohol intoxication or nitrous oxide inhalation.

The Great Blue Hole off the coast of Belize is the world's biggest ocean sinkhole, measuring 1,000 feet across and over 400 feet in depth. In 2018, an expedition led by billionaire Richard Branson and National Geographic Explorer Erika Bergman discovered the bodies of two divers at the bottom of the sinkhole. The cause of death was not confirmed, but one possible cause could have been nitrogen narcosis.

Nitrogen narcosis occurs when divers breathe compressed nitrogen, or other inert gases such as neon, argon, krypton, and xenon, from their tanks. The effects of nitrogen narcosis are highly variable among divers, with all divers being significantly impaired while breathing air at 60 to 70 meters, and some divers being affected as early as 30 meters. The effects are not progressive with time at a maintained depth, but symptoms progress and new symptoms develop as a diver descends deeper into greater pressures.

The symptoms of nitrogen narcosis begin with effects on higher functions such as judgment, reasoning, short-term memory, and concentration. The diver may also experience a euphoric or stimulating feeling similar to mild alcohol intoxication. As the diver descends further and the partial pressure of nitrogen in the blood increases, impairments in manual dexterity and further mental decline, including idea fixation, hallucinations, and eventually stupor and coma, occur.

Death from nitrogen narcosis can result from unconsciousness or from severely impaired judgment leading to an accident during the dive. Other factors that increase the risk of nitrogen narcosis include alcohol, fatigue, anxiety, and hypothermia. The effects of nitrogen narcosis are completely reversed within minutes of ascending to shallower depths, with no long-term effects.

A popular diving site

The Great Blue Hole in Belize is a popular diving site, attracting thousands of divers every year. It is located off the coast of Belize, close to the Centre of Lighthouse Reef, an atoll about 100km from the mainland city of Belize. It is one of the world's most famous diving zones and is renowned for its crystal-clear waters and diverse marine life.

The Great Blue Hole is the world's biggest ocean sinkhole, measuring 1,000 feet across and over 400 feet in depth. It was formed thousands of years ago as a limestone cave and was later submerged due to rising sea levels. The site was popularised in the 1970s by the legendary explorer Jacques Cousteau, who revealed its wonders to the world through his television series, "The Undersea World of Jacques Cousteau".

The moderate temperatures and calm conditions of the Blue Hole make it accessible to divers all year round. However, due to its intense depth, only experienced divers are advised to enter. The absence of water currents and acute temperature changes allows divers to explore the unique geological formations and clear waters of the sinkhole.

The Blue Hole is home to a variety of exotic fish and marine creatures, including nurse tip sharks, reef sharks, midnight parrotfish, and hammerhead sharks. It is also a part of the Belize Barrier Reef Reserve System, a UNESCO World Heritage Site. The surrounding reef and shallow waters provide a habitat for many other species, such as Caribbean reef sharks, nurse sharks, hammerhead sharks, and blacktip sharks.

Despite its beauty and popularity, the Great Blue Hole has also witnessed accidents and diver deaths. The absence of oxygen below 290 feet creates a "death zone", where anything that falls will be preserved due to the lack of oxygen. This zone has claimed the lives of divers who ventured too deep.

In conclusion, the Great Blue Hole in Belize is a fascinating and popular diving site that offers a unique underwater experience. However, it is important for divers to be aware of the potential dangers and ensure they have the necessary experience and equipment to explore this natural wonder safely.

One of the world's seven wonders?

The Great Blue Hole in Belize is a world-class destination for scuba divers, attracting thousands of divers with varying levels of experience. It is a large underwater sinkhole off the coast of Belize, near the centre of Lighthouse Reef, a small atoll 62 miles from the mainland. The Blue Hole is circular in shape, measuring 300 metres (984 feet) across and 125 metres (410 feet) deep.

The Blue Hole is the world's largest natural formation of its kind and is part of the Belize Barrier Reef Reserve System, a World Heritage Site of UNESCO. It was made famous by legendary oceanographer and diver Jacques Cousteau, who explored the site in the 1970s and declared it one of the top ten dive sites globally.

The Blue Hole is characterised by its clear waters and diverse marine life, including tropical fish, coral formations, nurse sharks, giant groupers, and several types of reef sharks. The internal structure of the Blue Hole has long been a mystery, with its depths remaining unexplored until Richard Branson's expedition in 2018.

The Blue Hole is distinguished by its striking circular shape and deep blue hue, encircled by the lighter shades of the surrounding reef. This contrast makes it visible even from space. The surrounding reef showcases a spectrum of blue-green tones, ranging from peacock-blue and turquoise to mesmerising shades of aquamarine.

The Blue Hole is not only a top diving destination but also a significant natural wonder. It is one of the seven wonders of Belize's World Heritage Site and was ranked number one by the Discovery Channel on its list of "The 10 Most Amazing Places on Earth".

The formation of the Blue Hole is attributed to the collapse of an underground cavern and cave system during the last ice age. It is believed that the structures within the Blue Hole, such as stalactites, stalagmites, and columns, were formed in a dry cavern above sea level during glacial periods. Analysis of stalactites reveals that their formation took place at various intervals, with the earliest dating back 153,000 years.

The Blue Hole serves as a reminder of the dangers of climate change, as sea levels continue to rise. Richard Branson, during his expedition, observed that the Blue Hole "is proof of how oceans can rise quickly and catastrophically."

The Blue Hole's natural beauty and ecological importance have led to its recognition as a UNESCO World Heritage Site. This designation aims to protect the site and preserve the experience for divers who venture into its depths.

Frequently asked questions