Great Blue Hole — blue hole
The TerraMar Project · CC BY 2.0

Great Blue Hole

  • 2 min read
  • 17.316° N 87.534° W
  • UNESCO World Heritage
  • UNESCO natural beauty

Interesting facts

  • A 30-metre sediment core drilled from its floor records 574 storms over 5,700 years, showing tropical cyclones becoming more frequent in recent decades.
  • Some stalactites deep in the shaft hang about 5 degrees off vertical, all in the same direction, showing that the limestone plateau itself once tilted.
  • Dating of its stalactites points to growth in a dry cave around 153,000, 66,000, 60,000 and 15,000 years ago.
  • Its surface covers about 70,650 square metres, close to the area of ten football pitches.
  • Jacques Cousteau rated it among the five best scuba diving sites in the world.
  • A 1997 expedition took core samples from the floor; every diver had to be certified in cave diving and mixed-gas breathing.
  • In 2012 the Discovery Channel put it first on its list of the ten most amazing places on Earth.
  • The 2018 submarine dives were broadcast live on television, with Jacques Cousteau's grandson Fabien Cousteau and Richard Branson taking part.
  • The reef rim lies only about 5 metres deep before sloping to around 10 metres and dropping away down a near-vertical wall.
  • Blacktip sharks, midnight parrotfish, Pederson's cleaner shrimp and neon gobies are among the residents of the rim.

Why it is worth it

The Great Blue Hole is a near-perfect circle of deep indigo set in the pale turquoise of Lighthouse Reef, an atoll some 70 kilometres off the coast of Belize. Seen from the air it looks unreal: a ring of coral about 318 metres across, with the water inside dropping away to around 124 metres. It is the centrepiece of the Blue Hole Natural Monument and part of the Belize Barrier Reef Reserve System, a UNESCO World Heritage Site.

The hole is a drowned cave. During the ice ages, when sea levels stood far lower than today, this was dry limestone country, and rainwater dissolved a cavern system in the rock until its roof collapsed into a vertical shaft. Stalactites, which only form in air, still hang from ledges deep under water; dating them has shown phases of growth at several points during the last glaciations, the most recent around 15,000 years ago. As the ice melted and the sea rose, the cave flooded, leaving a sunken sinkhole in the middle of a reef.

Its fame dates from 1971, when Jacques Cousteau brought his ship Calypso here and his team charted the shaft, finding ledges at about 21, 49 and 91 metres. Later explorations went further: a 2018 expedition with small submarines mapped the hole in three dimensions and found, at around 90 metres, a layer of hydrogen sulphide below which there is almost no oxygen. Nearer the surface the rim is alive with reef fish such as groupers, angelfish and butterflyfish, and divers descending the wall regularly meet Caribbean reef sharks and nurse sharks among the stalactites.

For all its celebrity, the Blue Hole is best understood as part of a larger picture. The atoll around it, the reef, the lagoon and the hole together make one of the most striking pieces of marine geography anywhere, a landscape whose shapes still record the last ice age.

Getting there

The Blue Hole lies about 73 km east of Belize City, in open sea. The international gateway is Philip S. W. Goldson International Airport (BZE) at Belize City; the small airstrip on Caye Chapel, about 68 km away, is not a practical route. Day trips by boat for divers and snorkellers leave early in the morning from San Pedro on Ambergris Caye and from Caye Caulker, taking roughly two and a half to three hours each way; scenic flights from Belize City, Caye Caulker and San Pedro circle the hole from the air.

On these lists

The Most Spectacular Blue Holes 5The Most Mystical Sinkholes 7The Most Mystical Natural Wonders 8The Most Spectacular Sinkholes 14The Most Beautiful UNESCO-Listed Natural Wonders 38The UNESCO Sites of Exceptional Natural Beauty 77The Most Mystical Places 138The Most Beautiful Water Wonders 429The Most Beautiful UNESCO World Heritage Sites 557The Most Beautiful Natural Wonders 580

From the encyclopaedia

The Great Blue Hole is a large marine sinkhole off the coast of Belize. It lies near the center of Lighthouse Reef, a small atoll 70 km (43 mi) from the mainland and Belize City. The hole is circular in shape, 318 m (1,043 ft) across and 124 m (407 ft) deep. It has a surface area of 70,650 square metres (760,500 sq ft). It was formed during several phases of the Quaternary glaciation when sea levels were much lower. Analysis of stalactites found in the Great Blue Hole shows that formation took place 153,000, 66,000, 60,000, and 15,000 years ago. As the ocean began to rise again, the cave was flooded. The Great Blue Hole is part of the larger Belize Barrier Reef Reserve System, a UNESCO World Heritage Site.

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