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The atoll of Tetiʻaroa in French Polynesia. An atoll (/ ˈ æ t. ɒ l,-ɔː l,-oʊ l, ə ˈ t ɒ l,-ˈ t ɔː l,-ˈ t oʊ l /) [1] is a ring-shaped island, including a coral rim that encircles a lagoon. There may be coral islands or cays on the rim. [2] [3] Atolls are located in warm tropical or subtropical parts of the oceans and seas where ...
Canton Island typifies the isolated coral atolls dotting the Pacific Ocean. The Structure and Distribution of Coral Reefs, Being the first part of the geology of the voyage of the Beagle, under the command of Capt. Fitzroy, R.N. during the years 1832 to 1836, was published in 1842 as Charles Darwin's first monograph, and set out his theory of the formation of coral reefs and atolls.
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Eventually the island completely subsides beneath the water, leaving a ring of growing coral with an open lagoon in its center. The process of atoll formation may take as long as 30,000,000 years to occur. Reason Not many people know what an atoll is. This is a simple explanation in a picture. Also, it is original. Articles this image appears ...
A coral reef is an underwater ecosystem characterized by reef-building corals.Reefs are formed of colonies of coral polyps held together by calcium carbonate. [1] Most coral reefs are built from stony corals, whose polyps cluster in groups.
Satellite picture of the Atafu atoll in Tokelau in the Pacific Ocean. Atoll lagoons form as coral reefs grow upwards while the islands that the reefs surround subside, until eventually only the reefs remain above sea level. Unlike the lagoons that form shoreward of fringing reefs, atoll lagoons often contain some deep (>20 m (66 ft)) portions.
There are two types of lagoons, coastal and oceanic/atoll lagoons. [19] A coastal lagoon is, as the definition above, simply a body of water that is separated from the ocean by a barrier. An atoll lagoon is a circular coral reef or several coral islands that surround a lagoon. Atoll lagoons are often much deeper than coastal lagoons. [20]
They are ridges of reef formed by coral ("spurs") separated by channels ("grooves") which often have sediment or rubble bed. Spur and groove formations vary in their size and distribution worldwide but are a common feature on many forereefs of fringing reefs , barrier reefs , and atolls which are exposed to moderate wave energy. [ 1 ]