Here’s something you don’t see everyday: the Great Blue Hole in Belize. This natural wonder is essentially a circular submarine sinkhole that measures over 1,000 feet (330 meters) across and 400 feet (120 meters) deep. This sea-hole was “formed as a limestone cave system during the last ice age – as the ocean began to rise again, the caves flooded, and the roof collapsed.” Continue reading for two videos, more pictures, and additional information.
This site was made famous by Jacques-Yves Cousteau, who declared it one of the top ten 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 5º in a consistent orientation, thus 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.
Initial measured depth of Great Blue Hole was 125 m (410 ft) which is the most often cited depth up to this day. An expedition by the Cambrian Foundation in 1997 measured the hole’s depth as 124 m (407 ft) at its deepest point. This difference in measurement can be explained by ongoing sedimentation or by imprecision in earlier measurements. The purpose of this expedition was the collection of core samples from the floor of the Blue Hole and documentation of the cave system. To accomplish these tasks, all of the divers had to be certified in cave diving and mixed gases.