From the air, the Great Blue Hole of Belize resembles an otherworldly maw, intent on drinking down the surrounding Lighthouse Reef Atoll. In reality, the 1,000-foot (305-meter) wide hole is simply a sinkhole in the ocean. Geologists believe that an underlying cave system collapsed under increased pressure some 10,000 years ago due to rising sea levels.
The dark hole descends 412 feet (126 meters), terminating in lightless depths where a lack of oxygen prevents most forms of life from thriving. Divers rarely plunge these depths, however, as most are content to explore the stalactite-rich caverns accessible from depths of some 130 feet (40 meters) below the surface.
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