…shape, and position of the coral sand cays, or “low islands,” that develop on reefs. They sometimes occur completely separate from other kinds of reefs. Larger patches occur as isolated parts of larger developments of any of the other three reef categories. Smaller patches occur inside atoll lagoons. Finally, there are patch reefs, which have irregular tablelike or pinnacle features. The third category of reefs consists of atolls, which are like circular barrier reefs but without their central landmass. Some barrier reefs are more or less circular, surrounding an island, but larger barrier reefs, such as those along the Red Sea coast and the Great Barrier Reef of Australia, are complex linear features consisting of chains of reef patches, some of them elongated into ribbon reefs. Barrier reefs are also close to a nonreef landmass but lie several kilometres offshore, separated from the landmass by a lagoon or channel often approximately 50 m (160 ft) deep. Fringing reefs consist of a flat reef area directly skirting a nonreef island, often volcanic, or a mainland mass. Geologically, the island is just one small part of the whole coral reef.Ĭoral reefs take four main forms. Reef building takes place mostly below high-tide level, and a typical coral island or cay usually surmounts the relatively flat top of the whole reef system. They may extend dozens of kilometres and include almost any tropical limestone island whose structure is integrally part of a living or relatively recent coral reef. Coral islands consist of low land perhaps only a few metres above sea level, generally with coconut palms and surrounded by white coral sand beaches. SpaceNext50 Britannica presents SpaceNext50, From the race to the Moon to space stewardship, we explore a wide range of subjects that feed our curiosity about space!Ĭoral island, tropical island built of organic material derived from skeletons of corals and numerous other animals and plants associated with corals.Learn about the major environmental problems facing our planet and what can be done about them! Saving Earth Britannica Presents Earth’s To-Do List for the 21st Century.Britannica Beyond We’ve created a new place where questions are at the center of learning.100 Women Britannica celebrates the centennial of the Nineteenth Amendment, highlighting suffragists and history-making politicians.COVID-19 Portal While this global health crisis continues to evolve, it can be useful to look to past pandemics to better understand how to respond today.Student Portal Britannica is the ultimate student resource for key school subjects like history, government, literature, and more.This Time in History In these videos, find out what happened this month (or any month!) in history.#WTFact Videos In #WTFact Britannica shares some of the most bizarre facts we can find.Demystified Videos In Demystified, Britannica has all the answers to your burning questions.Britannica Explains In these videos, Britannica explains a variety of topics and answers frequently asked questions.Britannica Classics Check out these retro videos from Encyclopedia Britannica’s archives.
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