40 Fun Facts About Great Blue Hole

Which undersea filmmaker made the Great Blue Hole famous when he explored it in 1971?

Jacques Cousteau sailed his research ship to Belize to chart the sinkhole's depths, and his team showed that it had once been a cave standing above the waves.

What did divers retrieve from caves inside the Great Blue Hole that proved the sinkhole had formed above sea level?

Stalactites form drip by drip in air-filled caves, so finding them underwater showed the hole stood dry before the seas rose. Some hang at a tilt, evidence that the land itself later shifted.

The Lusca, a monster of island folklore said to lurk in the blue holes of Andros, resembles which giant sea creature?

Octopus tentacles are the Lusca's trademark: a guide on Andros called it Him of the Hands and told a visiting diver tales of it grabbing fishermen and sinking ships.

Legend says which figure from Journey to the West found his golden cudgel in Dragon Hole, a 300-metre-deep blue hole?

The Monkey King's legend clings to a real place: Dragon Hole held the title of deepest known blue hole from 2016 until a rival was measured in 2024.

Sediment drilled from the Great Blue Hole strengthened the case that drought helped topple which ancient civilization?

Maya civilization collapsed between AD 800 and 1000, just when the hole's mud layers record far fewer storms. The sinkhole works like a giant bucket, trapping a record of past climate.

Which fruit names a deep blue hole off Sarasota, Florida, after a fishing captain saw its skin floating there?

Banana skin, a green one, gave Green Banana Hole its name. The sinkhole is shaped roughly like an hourglass, which makes it especially hard to explore.

The Blue Hole of Santa Rosa, a desert spring pool popular with scuba divers, sits beside which famous American highway?

Route 66 brought motorists right past the pool from the 1920s, and its steady 62 °F water has since made it one of America's most popular spots for dive training.

Blue holes look deep blue because seawater absorbs the other colours of sunlight; which colour is absorbed first?

Red light is soaked up first, then yellow and finally green, leaving blue to reach the white sand below and bounce back up.

Which British billionaire joined a submarine expedition to the bottom of the Great Blue Hole, broadcast live in 2018?

Richard Branson rode along as two submarines scanned the walls with sonar, producing the first 3D map of the hole's interior.

The Great Blue Hole lies near the centre of which atoll, about 70 kilometres off the coast of Belize?

Lighthouse Reef is one of only three atolls in Belize, and at low tide parts of the coral ring around the hole break the surface.

What was the name of the research ship that carried a famous undersea explorer to chart the Great Blue Hole in 1971?

Calypso was leased to her captain for a symbolic one franc a year, and John Denver's 1975 hit song of the same name was a tribute to the ship and her crew.

The Great Blue Hole belongs to a reef reserve system that earned which international designation in 1996?

World Heritage Site status covers seven protected areas along the reef, including the hole itself and the nearby island of Half Moon Caye.

Which television network ranked the Great Blue Hole first on its list of the ten most amazing places on Earth?

Discovery Channel came back in 2018 with a two-hour live special that followed submarines down to the floor of the sinkhole.

Which toxic gas forms a layer roughly 90 metres down in the Great Blue Hole, with dark, lifeless water beneath?

Hydrogen sulfide marks the point where the sunlight vanishes: a submarine pilot who passed through the layer in 2018 described total blackness beneath it.

Which type of shark, a sedentary bottom-dweller, lives in the Great Blue Hole alongside blacktips and reef sharks?

Nurse sharks often rest in groups by day and feed at night. The hole's coral rim starts about 5 metres down before dropping away as a near-vertical cliff.

The Great Blue Hole sits in the world's second-largest coral reef system; which country has the largest?

Australia's Great Barrier Reef is the only system bigger than the Mesoamerican reef, which runs along the coasts of four countries from the Yucatán Peninsula down to Honduras.

Which naturalist described Belize's barrier reef in 1842 as the most remarkable reef in the West Indies?

Charles Darwin published his theory of how coral atolls form that same year, drawing on his five-year voyage aboard HMS Beagle.

Which seabirds were the reason Half Moon Caye, near the Great Blue Hole, became a sanctuary in the 1920s?

Boobies with brightly coloured feet nest in the island's rare orange-flowered forest, and their droppings fertilise the very trees that shelter them.

The Great Blue Hole sits inside an atoll, a ring of coral reef that encloses which kind of shallow water body?

Lagoon water around the hole is only 2 to 6 metres deep, which is why the dark shaft, more than 120 metres deep, stands out so sharply from the air.

Taam Ja', measured in 2024 as the deepest known blue hole, lies in Chetumal Bay off the coast of which country?

Mexico's record-breaker was probed to more than 420 metres without the instruments finding the bottom, so its true depth is still unknown.

Local fishermen call Dragon Hole, a blue hole in the Paracel Islands, the eye of which body of water?

South China Sea coral around the hole lies under less than a metre of water, so researchers floated a flat-bottomed platform over it to lower their robot.

Dean's Blue Hole, a 202-metre-deep sinkhole in a bay near Clarence Town, is on Long Island in which island nation?

The Bahamas is home to Dean's Blue Hole, whose mouth, about 30 metres wide, opens into a cavern more than three times that across.

Dean's Blue Hole hosts Vertical Blue, an invite-only elite competition in which sport?

Freediving records fall here regularly: the first Vertical Blue, held over eleven days in 2008, produced 23 national and 3 world records.

William Trubridge, the first diver to pass 100 metres without fins, set records at Dean's Blue Hole for which country?

New Zealand became Trubridge's home at eighteen months old, after his birth in England, and he went on to run a diving school and an annual contest at the hole.

Which country is home to the Blue Hole of Dahab, a Sinai dive site nicknamed the Divers' Cemetery?

Egypt's diving authority stationed a policeman at the site to check that divers go down with a certified guide, after a long run of fatal accidents.

Which tunnel in Dahab's Blue Hole, its roof 55 metres below the surface, has claimed the lives of many divers?

The Arch looks under 10 metres long in the clear water but measures 26, and it lies well below the 40-metre limit usually set for recreational divers.

Which 2023 Netflix documentary about Italian record-chaser Alessia Zecchini features the deadly Blue Hole at Dahab?

The Deepest Breath premiered at the Sundance Film Festival and follows Zecchini's pursuit of a world record with the help of safety diver Stephen Keenan.

Blue holes differ from which inland sinkholes, famous across the Yucatán and usually filled with fresh groundwater?

Cenotes are inland pits holding fresh groundwater, while blue holes typically hold seawater, or a mix, that rises and falls with the tide.

Blue holes develop in banks and islands of carbonate bedrock, most often which rock that rainwater slowly dissolves?

Limestone exposed when sea levels stood more than 100 metres lower was eaten into caves and pits by rain, and the rising ocean later flooded them.

The deep water in most blue holes lacks which dissolved gas, making it hostile to fish but ideal for preserving fossils?

Oxygen runs out because the water barely circulates, and the same stillness lets mud settle in layers that record climate back to the last ice age.

Fossils of which large reptiles, along with tortoises, have been found preserved inside blue holes?

Crocodiles turn up as fossils alongside microscopic remains in the layered mud, which is why scientists prize blue holes as archives of past life and climate.

Divers inside the Blue Hole off Guam, a sinkhole in the reef near Apra Harbor, see its opening as which shape?

A heart is the outline divers see overhead as they drop into the shaft, which starts about 18 metres down and has a side exit onto the reef wall at 40 metres.

Castalia's Blue Hole, a pond once believed bottomless but only about 45 feet deep, lies in which US state?

Ohio's roadside wonder drew 165,000 visitors a year at its peak before closing to the public, and it now sits on the grounds of a private trout club.

In 2010 Belize, home of the Great Blue Hole, became one of the first countries to ban which fishing method outright?

Bottom trawling tows nets along the seafloor, and five years after outlawing it Belize also banned offshore oil drilling within a kilometre of its reef.

Which type of landscape, formed where water dissolves soluble bedrock, produces blue holes, sinkholes and caves?

Karst country drains underground, so it may have few or no rivers and lakes on the surface despite all the water at work below.

What name is given to the boundary in a blue hole where fresh water meets salt water and corrodes the rock?

Halocline chemistry eats sideways into the walls, carving horizontal passages that can run for hundreds of metres from the main shaft.

Dragon Hole's official name, Sansha Yongle Blue Hole, honours the third emperor of which dynasty?

Ming emperor Yongle seized the throne from his nephew after a three-year civil war and raised Beijing to the rank of capital.

The Blue Hole at Dahab opens onto which narrow gulf between the Sinai Peninsula and Arabia?

Aqaba's waters are so deep that just outside the hole's seaward wall the floor plunges to more than 1,000 metres.

The ship that charted the Great Blue Hole in 1971 began life during World War II as which type of naval vessel?

Minesweeper service in the Mediterranean came first; after the war the wooden-hulled vessel ran as a ferry between Malta and Gozo before being refitted for ocean research.

Which endangered reptiles nest each year from May to November on Half Moon Caye, beside the Great Blue Hole?

Sea turtles of three species, the loggerhead, hawksbill and green, come ashore on the island's south-eastern side to nest.