Great Blue Hole

The site was made famous by Jacques Cousteau, who declared it one of the top five scuba diving sites in the world. In 1971 he brought his ship, the Calypso, to the hole to chart its depths.{{cite book

|title=Galapagos – Titicaca – The Blue Holes (Hole)

|year=1973

|author=Jacques-Yves Cousteau

|author-link=Jacques-Yves Cousteau

|publisher=Cassell

|location=London

}} Investigations by this expedition confirmed the hole's origin as typical karst limestone formations, formed before rises in sea level in at least four stages, leaving ledges at depths of {{convert|21|m|ft|abbr=on}}, {{convert|49|m|ft|abbr=on}}, and {{convert|91|m|ft|abbr=on}}. Stalactites were retrieved from submerged caves, confirming their previous formation above sea level. Some of these stalactites were also off-vertical by 5˚ in a consistent orientation, indicating that there had also been some past geological shift and tilting of the underlying plateau, followed by a long period in the current plane. The tilt indicates that this was movement of the land, rather than a rise in sea level alone. The initial measured depth of the Great Blue Hole was about {{convert|125|m|ft|0|abbr=on}} which is the most often cited depth up to this day.

An expedition was conducted in the summer of 1997 to collect core samples from the Blue Hole's floor and document the cave system.{{cite book |author=Tysall, Terrance N |chapter=The Belize Blue Hole Exploration Project |editor1=Hamilton, RW |editor2=Pence, DF |editor3=Kesling, DE |title=Assessment and Feasibility of Technical Diving Operations for Scientific Exploration |publisher=American Academy of Underwater Sciences |year=1999 |url=http://archive.rubicon-foundation.org/9005 |access-date=2011-01-08 |archive-url=https://archive.today/20130416011226/http://archive.rubicon-foundation.org/9005 |archive-date=2013-04-16 |url-status=usurped }} To accomplish these tasks, all of the divers had to be certified in cave diving and mixed gases.

In December 2018, two submarines descended into the Blue Hole in an attempt to map its interior. Using sonar scanning, the team was nearly able to complete a 3-D map of the {{convert|1,000|ft|m|adj=mid|-wide}} hole. One of their discoveries was a layer of hydrogen sulfide at a depth of approximately {{convert|300|ft|m}}. The water at that depth and below becomes dark, anoxic and devoid of life.{{Cite web|last=Street|first=Francesca|title=Dispatches from the bottom of Belize's Blue Hole|url=https://www.cnn.com/travel/article/blue-hole-belize-expedition/index.html|access-date=2021-05-16|website=CNN|date=15 February 2019 |language=en}} The submarine expedition also discovered the bodies of two divers at the bottom, out of three believed to have gone missing while diving there, and reported them to Belizean authorities. Out of respect, the crew declined to bring the bodies back to land, thus leaving them buried at sea.{{cite web |url= https://www.techtimes.com/articles/240914/20190405/bodies-of-missing-divers-found-at-the-bottom-of-belize-great-blue-hole.htm |title=Bodies Of Missing Divers Found At The Bottom Of Belize Great Blue Hole |last=Carlos |first=Naia |work=Tech Times |date=2019-04-05 |access-date=2021-08-18}}

The Great Blue Hole is a popular destination for recreational scuba divers making day trips from the coastal tourist communities in Belize.{{citation needed|date=May 2024}}

On-shore caves of similar formation, as large collapsed sinkholes, are well known in Belize and in the Yucatán Peninsula, where they are known as cenotes. Unlike the mainland cenotes which often link to underwater cave systems, there is little evidence of horizontal development in the Blue Hole.{{cn|date=March 2021}}{{clarify|there must have been drainage channels to maintain sufficiently consistent water levels for speleothems to develop|date=March 2021}}

In 2012, Discovery Channel ranked the Great Blue Hole as number one on its list of "The 10 Most Amazing Places on Earth".{{cite web |author=Robert Lamb |author2=Amanda Arnold |year=2012 |title=The 10 Most Amazing Places on Earth |url=https://dsc.discovery.com/tv-shows/curiosity/topics/10-amazing-geological-features.htm |url-status=live |archive-url=https://web.archive.org/web/20121109235646/http://dsc.discovery.com/tv-shows/curiosity/topics/10-amazing-geological-features.htm |archive-date=2012-11-09 |access-date=2013-09-12 |publisher=Discovery Channel}} In 2018, they featured a two-hour special titled Discovery Live: Into the Blue Hole featuring Erika Bergman, Fabien Cousteau and Richard Branson.{{cite web|url=https://press.discovery.com/us/dsc/programs/discovery-live-blue-hole/|title=DISCOVERY LIVE: INTO THE BLUE HOLE|access-date=December 3, 2018}}

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Category:Caves of Belize

Category:Landforms of Belize

Category:Mesoamerican Barrier Reef System

Category:Sea caves

Category:Sinkholes of North America

Category:Underwater diving sites in Belize