Cave system
Great Blue Hole
Belize Audubon gives 412 ft (about 125 m); widely cited figures range from 124 m to 125 m.
A circular marine sinkhole about 300 m across and 125 m deep on Lighthouse Reef, Belize, formed by the collapse of a cave during ice-age low sea levels. Stalactites hang beneath ledges on its walls; it is protected as a natural monument.
The Great Blue Hole is a near-circular submerged sinkhole in the middle of Lighthouse Reef atoll. The Belize Audubon Society describes it as a collapsed cave roughly 1,000 ft (about 300 m) across and about 412 ft (about 125 m) deep, with sheer walls and overhanging shelves that carry stalactites.
The formations show that the hole was once a dry cave. Belize Audubon dates its formation to the Pleistocene, when sea level was much lower; the cave roof collapsed and the hole was later drowned by the rising sea. Jacques Cousteau's 1971 expedition on the Calypso charted the hole and recovered stalactites, and the tilt of some formations has been cited as evidence that the land has shifted since they formed.
Most divers arrive on boat trips from the cayes, the mainland or atoll resorts. Published dive descriptions focus on the stalactite-hung overhangs on the wall, and one operator lists a maximum depth of 40 m for its Blue Hole dive; no cave penetration route is published. Below about 90 m the water contains hydrogen sulfide and has no oxygen, as a 2018 submarine survey reported.
The hole has been protected since 1996 as the Blue Hole Natural Monument and is part of the Belize Barrier Reef Reserve System World Heritage Site.
Geology
A submerged collapse sinkhole in karst limestone, formed in the Pleistocene (Belize Audubon estimates roughly 15,000 years ago). Stalactites and stalagmites under its overhangs formed in air and were later drowned; the tilt of some has been cited as evidence of tectonic tilting.
Water, flow and flooding
A 2018 submarine expedition reported a hydrogen sulfide layer at about 290-300 ft (roughly 90 m), below which the water is anoxic. The floor holds a thick, undisturbed sediment layer that records past deposition.
Why it matters
A drowned cave whose stalactites and ledges record former low sea levels. It is protected as a natural monument within a UNESCO World Heritage property.
Survey and exploration history
| 1971 | Jacques Cousteau's Calypso expedition charted the hole and recovered stalactites from its submerged caves. [5] |
| 1996 | The site was declared the Blue Hole Natural Monument. [1] |
| 2018-12 | A submarine expedition led by Aquatica Submarines mapped the hole with sonar and reported a hydrogen sulfide layer near 90 m. [3] |
Entrances and dive sites
One open entrance: the sinkhole itself, with mooring buoys for dive boats. No land.
For orientation, not navigation. Hollow dots are approximate.
Further reading
Every fact on this page, with its source (9)
| Fact | Status | Source |
|---|---|---|
| The sinkhole is about 412 ft (about 125 m) deep and roughly 1,000 ft (about 300 m) across.Belize Audubon; an operator gives over 300 m wide and 125 m deep. | Verified | [1] [2] |
| It is a submerged collapsed cave formed in the Pleistocene, about 15,000 years ago, with overhanging shelves carrying stalactites; tilted stalactites are cited as evidence of tectonic tilting. | Verified | [1] |
| A hydrogen sulfide layer lies at about 290 ft, with no oxygen below it.Reported from the December 2018 Aquatica expedition; Wikipedia gives about 300 ft (91 m). | Reported | [3] |
| Jacques Cousteau's 1971 expedition charted the hole and recovered stalactites.Wikipedia used for orientation; cites Cousteau (1973). | Reported | [5] |
| The Blue Hole Natural Monument was designated in 1996 and is part of the Belize Barrier Reef Reserve System World Heritage Site. | Verified | [1] |
| Most visitors reach the site with tour operators from San Pedro, Caye Caulker, Hopkins, Placencia and atoll resorts; mariners must contact Half Moon Caye rangers on VHF 16 before mooring. | Verified | [1] |
| Non-nationals pay BZD 60 per day; hours are 8:00-16:30.Belize Audubon page checked 2026-10-14; the national fee is shown ambiguously on the page. | Verified | [1] |
| One operator lists a 40 m maximum depth for its Blue Hole dive, listed for advanced-certified divers, and a minimum age of 18 for the Blue Hole dive.Provider claim; not a park rule. | Reported | [2] |
| The Great Blue Hole is at about 17.3153 N, 87.5344 W.GeoNames and Wikipedia agree. | Reported | [4] [5] |
Verified: stated by an official or primary source we opened. Reported: from a secondary source only. Sources conflict: the note gives both versions. May be out of date: the newest source we found is old.
Written in our own words from the sources above. Report a correction