<P> The Great Blue Hole is a giant 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 was formed during several episodes of 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 a part of the larger Belize Barrier Reef Reserve System, a World Heritage Site of the United Nations Educational, Scientific and Cultural Organization (UNESCO). </P> <P> This 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 . 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 21 m (69 ft), 49 m (161 ft), and 91 m (299 ft). 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 a movement of the land, rather than a rise in sea level alone . </P>

Where is the blue hole located in belize