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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.
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 ]
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 ...
Gahaafaru Atoll also known as Gaafaru Atoll or Gaafarufalhu is a small atoll at the eastern end of a large elliptical reef that has proved disastrous to many vessels with the wrecks of Aracan (1873), SS Seagull (1879), Clan Alpine (1879), Erlangen (1894), Crusader (1905) and Lady Cristine (1974). 15 kilometres (9.3 miles) long and 8.5 ...
A barrier reef can encircle an island, and once the island sinks below sea level a roughly circular atoll of growing coral continues to keep up with the sea level, forming a central lagoon. Barrier reefs and atolls do not usually form complete circles but are broken in places by storms.
As stated, the coral reefs such as fringing reefs, deep reefs, patch reefs and spur and groove formation are distributed over three islands in the Virgin Islands which are St. Croix (Salt River Bay National Historical Park and Ecological Preserve, Buck Island Reef National Monument), St. Thomas, and St. John (Virgin Islands Coral Reef National Monument).
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]
The atolls of the Indispensable Reef are aligned in a NW-SE direction: [1] North Reef is 18 km (11 mi) long, and up to 7 km (4.3 mi) wide. The rim of the atoll has two narrow openings in the north and northwest. The reef has a total area of 100 km 2 (39 sq mi), including lagoon and reef flat. There are no islets. Middle Reef is 51 km (32 mi) long.