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The Great Blue Hole is a large submarine sinkhole off the coast of Belize. It lies near the center of Lighthouse Reef, a small atoll from the mainland and Belize City. The hole is circular in shape, over across and 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.〔(【引用サイトリンク】publisher=NASA )〕 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).〔 (【引用サイトリンク】publisher=IUCN/WCMC )〕 ==Exploration and name== This site was made famous by Jacques 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 , , and . 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. Initial measured depth of Great Blue Hole was 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 〔 at its deepest point. This difference in measurement can be explained by ongoing sedimentation or by imprecision in measurements. The expedition's goal was to collect core samples from the Blue Hole's floor and document the cave system. To accomplish these tasks, all of the divers had to be certified in cave diving and mixed gases.〔 The actual name of “The Great Blue Hole” was created by British diver and author Ned Middleton after having lived in the country for six months. So impressed with this natural feature, he reasoned in his book “Ten Years Underwater” (Immel Publishing 1988, ISBN 0907151434) that if Australia could have ‘The Great Barrier Reef’ then Belize could equally have ‘The Great Blue Hole’ – thus setting this feature apart from similar, albeit smaller structures. This was later reinforced by his second book “Diving Belize” (AquaQuest publishing, USA 1994 ISBN 1881652017). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Great Blue Hole」の詳細全文を読む スポンサード リンク
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