Coral atoll - definition of Coral atoll by The Free Dictionary Coral atoll - definition of Coral atoll by The Free Dictionary Also found in: Thesaurus , Encyclopedia , Wikipedia . atoll An atoll is created as a coral reef builds up around an eroding volcanic island. a·toll (ăt′ôl′, -ŏl′, ā′tôl′, ā′tŏl′) n. An island or chain of islets connected by a coral reef that nearly or entirely encloses a lagoon. [Dhivehi atholhu; probably akin to Sinhalese ätul, interior (from the interior lagoon), probably from Sanskrit *antala-, interior, variant of antara-; see en in the Appendix of Indo-European roots.] atoll (Physical Geography) a circular coral reef or string of coral islands surrounding a lagoon [C17: from atollon, native name in the Maldive Islands] at•oll (ˈæt ɔl, -ɒl, -oʊl) n. a ring-shaped coral reef or a string of closely spaced small coral islands, enclosing or nearly enclosing a shallow lagoon.

[1615–25; earlier atollon < French] atoll An atoll develops (from left to right) when a volcanic island erodes and a ring of coral grows up around it. The depression left by the crater of an eroding volcano fills with water, forming a lagoon. a·toll A coral island forming a ring that nearly or entirely encloses a shallow lagoon. atoll A ring-shaped coral reef enclosing a lagoon. ThesaurusAntonymsRelated WordsSynonymsLegend: atoll - an island consisting of a circular coral reef surrounding a lagoon coral reef - a reef consisting of coral consolidated into limestone Translations Want to thank TFD for its existence? Tell a friend about us , add a link to this page, or visit the webmaster's page for free fun content . Link to this page: Kanton Island References in periodicals archive ? Home to two Unesco World Heritage sites, the archipelago shares a curious Arab connection: the fabled Aldabra, the world's largest raised coral atoll, first seen by early Arab seafarers of the 9th century A.

BP starts drilling Atoll-1 well offshore Egypt In 1996, Sacks and two colleagues went to the tiny coral atoll of Pingelap, a dot on the map of Micronesia where 10% of the population share a genetic eye condition. Japan wins rights to explore for rare metals in Pacific It is the largest raised coral atoll in the world and its dense forest has a canopy averaging 20 meters in height, and the forest is an essential component of the atoll, which is considered a true natural laboratory for scientific study, it said. UNESCO inscribes East Rennell of Solomon Islands on list of world heritage in danger According to TIGHAR, the 18-person research crew aims to locate, identify, and photograph any and all surviving aircraft wreckage that they believe may be in the deep waters surrounding Nikumaroro (formerly Gardner Island), an uninhabited coral atoll in the southwestern-Pacific Republic of Kiribati. -Expedition team plans search for Amelia Earhart plane Enhanced analysis of the image appears to show the landing gear of an aircraft protruding from the waters off Gardner Island, a tiny uninhabited coral atoll, 2,000 miles north west of Australia.

Atoll | Define Atoll at Dictionary.com atoll [at-awl, -ol, -ohl, uh-tawl, uh-tol, uh-tohl] /ˈæt ɔl, -ɒl, -oʊl, əˈtɔl, əˈtɒl, əˈtoʊl/ Spell noun 1. a ring-shaped coral reef or a string of closely spaced small coral islands, enclosing or nearly enclosing a shallow lagoon. Origin of atoll Expand 1615-1625 1615-25; earlier atollon < French: a word used in early descriptions of the Maldive Island atolls; said to be Divehi (Indo-Aryan language of the Maldives) atoḷu Dictionary.com Unabridged Examples from the Web for atoll Expand Amelia Earhart Breakthrough? Don’t Bet On It Clive Irving June 2, 2012 Plus, Kate and William could hardly have picked a worse time for their luxury vacation to a resort in Noonu atoll.

ANOTHER Vacay for Kate and William Tom Sykes March 5, 2014 Historical Examples But there is a third kind of reef, of very common occurrence in the Pacific and Indian Oceans, which goes by the name of "atoll." British Dictionary definitions for atoll Expand a circular coral reef or string of coral islands surrounding a lagoon Word Origin C17: from atollon, native name in the Maldive Islands Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012 Word Origin and History for atoll Expand n. 1620s, atollon, from Malayam atolu "reef," probably from adal "closing, uniting." Popularized in present form by Darwin's writings.

Online Etymology Dictionary, © 2010 Douglas Harper atoll (āt'ôl', ā'tôl') A coral island or series of coral islands forming a ring that nearly or entirely encloses a shallow lagoon. Atolls are surrounded by deep ocean water and range in diameter from about 1 km (0.62 mi) to over 100 km (62 mi). They are especially common in the western and central Pacific Ocean and are believed to form along the fringes of underwater volcanoes. Compare barrier reef , fringing reef. The American Heritage® Science Dictionary Copyright © 2002. Published by Houghton Mifflin. All rights reserved. ring-shaped - definition of ring-shaped in English | Oxford Dictionaries Having the shape of a ring; circular.

‘ring-shaped islands made of coral’ ‘a ring-shaped cake’ More example sentences ‘While the red, scaly, ring-shaped lesions on your skin can be unattractive, they generally aren't serious.’ ‘In the Rhone Valley, there is a ring-shaped, anis-flavoured roll, called rioute and eaten as a snack with wine, which is also briefly boiled before baking.’ ‘In the Harry Potter books, Quidditch players fly through the air on their broomsticks over an oval-shaped pitch and attempt to get balls through elevated ring-shaped goals.’ ‘The family spent Christmas Day snorkelling on the ring-shaped coral reef.’ ‘Engineers and scientists are fascinated by the apparently near-magical properties of ring-shaped objects.’ ‘A ring-shaped hole has been cut in the hedge, through which a vista stretching 10 miles to St Paul's Cathedral can be seen.’ ‘An atoll is a ring-shaped coral reef enclosing a shallow lagoon.’ ‘The virus causes unsightly ring-shaped blemishes and drastically reduces the amount of fruit that a tree would otherwise produce.’ ‘The infection is characterized by an itchy, red, often ring-shaped rash in these warm, moist areas of your body.’ ‘Bagels, like other

 ring-shaped objects, soon became the standard gift for women in childbirth because they were said to bring good luck and possess magical powers.’ Synonyms Which is the correct spelling?

besmirch Which is the correct spelling? mootch Which is the correct spelling? attach Which is the correct spelling? speetch Which is the correct spelling? watch Which is the correct spelling? sutch Which is the correct spelling? butterscotch Which is the correct spelling? sandwitch Which is the correct spelling? beach Which is the correct spelling? witch You scored /10 practise again? Retry Atoll - Encyclopedia Atoll GEOGRAPHICAL NAMES ATOLL (native name atollon in the Maldive Islands), a horseshoe or ring shaped coral reef enclosing a lagoon. The usual shape is that of a partly submerged dish with a broken edge, forming the ring of islands, standing upon a conical pedestal. The dish is formed of coral rock and the shells of various reefdwelling mollusca, covered, especially at the seaward edges, with a film of living coral polyps that continually extend the fringe, and enlarge the diameter of the atoll.

The lagoon tends to deepen when the land is stationary by the death of the coral animals in the still water, and the patchy disintegration of the "hard" coral, while waves and storms tear off blocks of rock and pile them up at the margin, increasing the height of the islands, which become covered by vegetation. The lagoon entrance in the open part of the horse-shoe is always to leeward of prevailing winds, since the coral growth is there slower than where the waves constantly renew the polyps' food supply. The conical pedestal rising from the depths is frequently a submarine volcanic cone or island, though any submerged peak may be crowned by an atoll. For the theory of atoll formation see Coral-Reefs. - Please bookmark this page (add it to your favorites). - If you wish to link to this page, you can do so by referring to the URL address below this line. Copyright © 1995-2011 ITA all rights reserved.

Encyclopedia Alphabetically 1911 Encyclopædia Britannica/Atoll - Wikisource, the free online library 1911 Encyclopædia Britannica/Atoll 604412 1911 Encyclopædia Britannica , Volume 2 — Atoll ATOLL (native name atollon in the Maldive Islands), a horse-shoe or ring shaped coral reef enclosing a lagoon. The usual shape is that of a partly submerged dish with a broken edge, forming the ring of islands, standing upon a conical pedestal. The dish is formed of coral rock and the shells of various reef-dwelling mollusca, covered, especially at the seaward edges, with a film of living coral polyps that continually extend the fringe, and enlarge the diameter of the atoll. The lagoon tends to deepen when the land is stationary by the death of the coral animals in the still water, and the patchy disintegration of the “hard” coral, while waves and storms tear off blocks of rock and pile them up at the margin, increasing the height of the islands, which become covered by vegetation.

The lagoon entrance in the open part of the horse-shoe is always to leeward of prevailing winds, since the coral growth is there slower than where the waves constantly renew the polyps’ food supply. The conical pedestal rising from the depths is frequently a submarine volcanic cone or island, though any submerged peak may be crowned by an atoll. For the theory of atoll formation see Coral-reefs . Atoll - definition of atoll by The Free Dictionary Atoll - definition of atoll by The Free Dictionary Related to atoll: Midway Atoll atoll An atoll is created as a coral reef builds up around an eroding volcanic island. a·toll (ăt′ôl′, -ŏl′, ā′tôl′, ā′tŏl′) n. An island or chain of islets connected by a coral reef that nearly or entirely encloses a lagoon.

[Dhivehi atholhu; probably akin to Sinhalese ätul, interior (from the interior lagoon), probably from Sanskrit *antala-, interior, variant of antara-; see en in the Appendix of Indo-European roots.] atoll (Physical Geography) a circular coral reef or string of coral islands surrounding a lagoon [C17: from atollon, native name in the Maldive Islands] at•oll (ˈæt ɔl, -ɒl, -oʊl) n. a ring-shaped coral reef or a string of closely spaced small coral islands, enclosing or nearly enclosing a shallow lagoon. [1615–25; earlier atollon < French] atoll An atoll develops (from left to right) when a volcanic island erodes and a ring of coral grows up around it. The depression left by the crater of an eroding volcano fills with water, forming a lagoon. a·toll A coral island forming a ring that nearly or entirely encloses a shallow lagoon. atoll A ring-shaped coral reef enclosing a lagoon.

ThesaurusAntonymsRelated WordsSynonymsLegend: atoll - an island consisting of a circular coral reef surrounding a lagoon coral reef - a reef consisting of coral consolidated into limestone Translations Want to thank TFD for its existence? Tell a friend about us , add a link to this page, or visit the webmaster's page for free fun content . Link to this page: Kanton Island References in classic literature ? I live on an atoll, a low island, it is a strip of land surrounding a lagoon, and its beauty is the beauty of the sea and sky and the varied colour of the lagoon and the grace of the cocoa-nut trees; but the place where Strickland lived had the beauty of the Garden of Eden. View in context In such way had vanished all the worlds and harbours and roadsteads and atoll lagoons where the Ariel had had lifted her laid anchor and gone on across and over the erasing sea-rim. From Malaita the Ariel steered west of north to Ongtong Java and to Tasman--great atolls that sweltered under the Line not quite awash in the vast waste of the West South Pacific.

View in context The atoll of Hikueru lay low on the water, a circle of pounded coral sand a hundred yards wide, twenty miles in circumference, and from three to five feet above high-water mark. Half an hour later, Huru-Huru, watching from the seaward side of the atoll, saw the two boats hoisted in and the Aorai pointing her nose out to sea. Miles in length, carrying tens of thousands of tons in weight, its impact shook the frail atoll like an earthquake. This was the highest spot of land in miles, and already, in many places on either hand, the great seas were making a clean breach of the slender ring of the atoll and surging into the lagoon. Even as Captain Lynch spoke, a great watery mass smote the atoll. Atolls - Credo Reference Topic Page: Atolls Definition: atoll from Philip's Encyclopedia Ring-shaped reef of coral enclosing a shallow lagoon. An atoll begins as a reef surrounding a slowly subsiding island, usually volcanic. As the island sinks, the coral continues to grow upwards until eventually the island is below sea level and only a ring of coral is left at the surface.

Summary Article: ATOLLS from Encyclopedias of the Natural World: Encyclopedia of Islands Image from: An atoll starts to form as soon as a volcano... in Guide to the Oceans Atolls are a special type of coral reef complex formed in tropical seas by a ring of reef coral enclosing a lagoon. The characteristic features of an atoll include a reef rim, from 100 to 500 m across, which is mainly awash at high tide, and flattish islands (motu), which remain a few meters above sea level and on which people may live. The word atoll itself comes from the language of the Maldive Islands, a chain of large atolls in the Indian Ocean (Fig. 1). Atolls range in size from a few to as many as 40,000 km2, and lagoon depths range from almost nothing to as much as 100 m. Air view of southern part of the Maldive chain of atolls in the (cloudy) Indian Ocean. Taken looking north from 2.4° N, 73.3° E.

Kolu-madulu Atoll, in center (at 2°25' N, 73°10' E), is about 50 km across. NASA photograph STS037-97-46. Image courtesy of the Image Science and Analysis Laboratory, NASA Johnson Space Center. DISTRIBUTION The minimum water temperature for the approximately 600 atolls around the globe is about 20 °C, a temperature that prevails from about 24° N to 29° S. Reef-building corals are partly dependent on their embedded photosyn-thesizing algal symbionts for adequate oxygen, and thus grow healthily only in lighted waters less than a few tens of meters deep. Slow-growing, deep-water coral reefs, without algal symbionts, are known to exist at depths down to about 6000 m. Many atoll lagoons are connected directly to the sea by inlet channels, but few channels are wide or deep enough to be navigable by anything but canoes. Atolls with wide, deep channels are favored for tourism and for administrative headquarters.

People from other atolls in the region tend to migrate to these centers, and overcrowding is a problem on some. The main source of income on most atolls is copra from coconuts, and tourism is important on a few. THE REEF RIM Between the ocean and the lagoon, the reef comprises an outer, wave-resistant algal ridge a few tens to a hundred meters wide at sea level, against which the ocean swell breaks. Seaward, the ridge drops steeply off into deeper, less turbulent water, and corals thrive along these slopes. The outer part of the algal ridge is commonly notched to a depth of 10–20 m by a reticulate network of narrow (1–3 m) grooves and surge channels that funnel water across the reef rim toward the lagoon. Behind the algal ridge is a reef flat, close to low tide level, where a pavement of living and dead coral and coral debris from the size of sand grains to the size of boulders extends lagoonward. Reef debris thrown onto the flat during typhoons lies in patches and windrows 1–2 m high in some places.

Large and small islands, termed motu, surmount the reef flat in places and rise to as much as 4 m above sea level (Fig. 2). They are commonly edged by a steep scarp toward the sea, created by waves beating against the island. It is only on these islands that the people of the atolls can live, where they are safely above the surf. The motu are weathered remnants of reef flats dating from the time of a regionally (in low latitudes) higher stand of sea level, about 2000–4000 years ago. The highstand resulted from the isostatic response to a redistribution of ocean waters after deglaciation of the northern continental ice sheets, beginning about 18,000 years ago. Between motu are shallow channels (hoa) that direct washover from ocean waves toward the lagoon. Shallow lakelike depressions, termed faros, pock reef flats on some atolls. These are the now-drowned remnants of karstic depressions dissolved by meteoric waters during the last lowstand of sea level.

In addition to carefully collecting and storing rainwater, atoll islanders depend on a precarious groundwater supply beneath the motu, which accumulates as a freshwater lens floating on the denser saltwater beneath. Seepages of this water are used to water vegetable gardens, and wells tap the lens for potable water. Leeward side of Tikehau atoll in the Tuamotu archipelago (15° S, 148° W), showing closely spaced surge channels next to the shore, the reef flat surmounted by wooded motu separated by channels (hoa) leading to the lagoon. The opposite shore of the lagoon is visible in the background as a dark line. Photograph by Pierre Labout, with permission of the Institut de Recherche pour le Développement, Paris. LAGOONS Atoll lagoons are mainly of fairly normal ocean salinity, except for completely landlocked lagoons surrounded by relatively high islands. These lagoons may include shallow salt pans and briny lakes. Detailed charts of atoll lagoons commonly show patch reefs, some rising to sea level but others submerged so as to constitute hazards to navigation.

Sediment builds up in the lagoon almost entirely during sea-level highstand times, when ocean waves can wash fine sediment across the reef. Shells of organisms living in the lagoon add to this thickness. At lowstand times, rain falling into the perched lagoonal depression may drain to the surrounding sea through erosional channels cut through the reef rim. ORIGIN OF THE ATOLL FORM The origin of the ring-around-a-lagoon form has attracted the attention of geologists for two centuries, beginning with Charles Darwin (1842), who never actually visited an atoll during his Beagle voyage but made a painstaking study of charts, supplemented by his own observations on other coral-surrounded islands. He showed that tropical islands displayed a series of reef forms, from fringing reefs that cling to the shore, to barrier reefs separated from the island shore by a lagoon, to atolls, with a lagoon but no bedrock island.

From his experiences in South America, where his hikes took him to shelly marine deposits high on the Andes slopes, connoting tectonic uplift, he reasoned that there must be a compensating subsidence in the Pacific basin and that the array of reef forms–fringing, barrier, atoll–must be due to regional subsidence of the islands. According to Darwin, the original fringing reef would grow upward, keeping pace with the relative rise of sea level during island subsidence, but as subsidence continued, the original fringing reef would continue to grow upward, and coral growth would be inhibited in the less turbulent and less fertile waters inland from the reef front. The perimeter would keep up with the rising sea level, whereas the more interior parts of the reef would fall further and further behind, resulting in a lagoon, first behind a barrier reef and then within an atoll. (Fig.

3) Since Darwin's theory was published, in 1842, the reality of island subsidence has been confirmed by the drilling of atolls in several places, starting with a testing expedition by the Royal Society to the Pacific atoll of Funafuti, in the Ellice Islands, in 1896-1898, The drill reached a depth of 340 m, at a level near the Pleistocene-Pliocene boundary (~2 million years old according to Ohde et al. 2002) in dolomitized reefal deposits, a finding that demonstrated rapid subsidence of the island foundations. Later drilling at Bikini and Enewetak (Eniwetok) atolls in the Marshall Islands, as part of the nuclear bomb testing program, reaffirmed the subsidence theory. The history of reef construction at Enewetak goes back some 50 million years, to Eocene times. The stages in the evolution of an atoll, according to Darwin (1842).

(A) A subsiding island is first girt by a fringing reef; then, as subsidence continues, the island is surrounded by a barrier reef, with a lagoon formed because growth rates of "interior" corals do not keep pace with better nourished "exterior" corals. (B) Continued subsidence, with the same growth-rate difference, leads to disappearance of the island and to an atoll form. Difficulties with Darwin's hypothesis for the origin of the lagoon provoked others (e.g., Daly 1915) to advocate other schemes, mainly in hypothesizing planation (including dissolution) of carbonate banks during lowered sea-level periods followed by construction of a perimeter reef during the following sea-level rise, thus leaving a central lagoon. These hypotheses were disproved by drilling at Bikini, Enewetak, and Mururoa, as part of nuclear bomb testing, which showed no such erosive platform.

THE DISSOLUTION, OR KARST, THEORY The Darwinian hypothesis for the origin of the lagoon has been replaced gradually by the dissolution, or karst, theory, in which the lagoonal depression is caused by dissolution of the reef carbonate by rainwater during periodic lowstands of sea level in the Pleistocene, when the sea level dropped repeatedly by about 100 m, on a 100,000-year time scale. The freshwater dissolved a hollow in the emergent carbonate bank, a hollow that was later filled with seawater when the sea level rose again. The two most important controls on lagoon depth are rainfall catchment area and average rainfall. The bigger the atoll and the rainier the climate, the deeper the lagoon. Present-day global rainfall patterns (Fig. 4) probably reasonably reflect rain patterns (wet north and south of the equator, with an equatorial dry belt in the eastern Pacific) during drier glacial times. Erosion of the atoll rim, generally by about 8 m, occurs during lowstands, but the rim is rebuilt during sea-level rise, and then still more rim carbonate is added during slow tectonic subsidence at highstand times.

At Enewetak atoll, drilling shows that since Eocene times, a flattish carbonate bank built up to a thickness of about 1400 m, keeping pace with tectonic subsidence, but interrupted from time to time by periods of emergence, when soils developed. The drilling and seismic work there also showed that the atoll form itself likely did not develop until Pleistocene times, when sea-level fluctuations were large and glacial intervals long, whereas earlier sea-level fluctuations were of lesser magnitude and duration. Atolls are thus mainly a phenomenon of the Pleistocene. THE FUTURE OF ATOLLS Atolls and their peoples are threatened today both by wave attacks on the fragile motu and by rising sea levels associated with global warming. These combine to reduce atoll relief to ephemeral patches of storm debris on reef flats awash at high tide. This is to say nothing of the threats to healthy coral growth posed by high water temperatures and possible increasing acidification of the ocean. Very high carbon dioxide levels probably occurred during the Cretaceous, a time of global warmth but also of very healthy populations of calcareous animals and plants.

Whatever trends toward major acidification in the Cretaceous world existed were partly offset by dissolution of calcareous sediments on the deep seafloor. Ultimately, the same balancing may happen in the modern ocean, but this will take time. Over the shorter term, Waterworld awaits. Average annual rainfall in millimeters per year for the 17-year period from 1979 to 1995. Interpolated and modified from Xie and Arkin (1997). SEE ALSO THE FOLLOWING ARTICLES Darwin and Geologic History / Makatea Islands / Marshall Islands / Motu / Reef Ecology and Conservation FURTHER READING Daly, R. A. 1915. The glacial control-theory of coral reefs. Proceedings ofthe American Academy of Arts and Sciences 51: 51-251. Darwin, C. 1962. The structure and distribution of coral reefs. Men-ard, H. W., ed. Berkeley: University of California Press. Dickinson, W. R. 2003. Impact of mid-Holocene hydro-isostatic highstand in regional sea level on habitability of islands in Pacific Oceania.

Journal of Coastal Research 19: 19-502. Purdy, E. G., and Winterer, E. L.., 2001. Origin of atoll lagoons. Geological Society of America Bulletin 113: 837-854. EDWARD L. WINTERER MLA Winterer, E. L., & WINTERER, E. L. (2009). Atolls. In R. G. Gillespie, & D. A. Clague (Eds.), Encyclopedias of the natural world: encyclopedia of islands. Berkeley, CA: University of California Press. Retrieved from Winterer, Edward L., and EDWARD L. WINTERER. "Atolls." In Encyclopedias of the Natural World: Encyclopedia of Islands, edited by Rosemary G. Gillespie, and David A. Clague. University of California Press, 2009. Winterer, E.L. and WINTERER, E.L. (2009). Atolls. In R.G. Gillespie & D.A.

Clague (Eds.), Encyclopedias of the natural world: encyclopedia of islands. Online. Berkeley: University of California Press. Available from: [Accessed 2 January 2017]. Winterer, Edward L., and EDWARD L. WINTERER. "Atolls." Encyclopedias of the Natural World: Encyclopedia of Islands, edited by Rosemary G. Gillespie, and David A. Clague, University of California Press, 2009. Credo Reference, Accessed 02 Jan 2017. Images atoll - definition of atoll in English | Oxford Dictionaries Definition of atoll in English: atoll A ring-shaped reef, island, or chain of islands formed of coral.

Example sentences ‘Banaba is a raised limestone island, but the other islands are all coral atolls, and most have lagoons.’ ‘In their voyage through the remote islands and atolls they seldom took the boy ashore, fearing infection.’ ‘There are at least 1000 islands in the chain of 19 atolls which make up the Maldives.’ ‘The Philippines is an archipelago of 7,100 islands, islets, and atolls located southeast of the Asian mainland.’ ‘Chants and oral traditions suggest native Hawaiians also visited other islands and atolls in the chain.’ ‘She had chosen a peaceful, romantic holiday in the southern atolls on a small island with only 50 huts.’ ‘Hidden beneath the salty Pacific, the coral atolls along the northwestern Hawaiian chain put an abrupt end to many a daring seafarer's adventure.’ ‘Acknowledged as the world's greatest dive destination, however, are the Maldive Islands in the Indian Ocean with enough coral atolls and underwater life to satisfy the most demanding diver.’ ‘On outer islands and atolls, however, most matters are settled internally, with little reliance on the state judicial apparatus.’ ‘The islands, atolls and reefs

 are believed to sit atop vast mineral and oil deposits.’ ‘The islands of the Maldives are grouped in ring-shaped coral atolls, each enclosing a relatively shallow lagoon with a flat sandy bottom.’ ‘The Marshall Islands are a group of low-lying coral atolls and islands in the central Pacific Ocean.’ ‘Tuvelu is one of the smallest countries on earth, a chain of nine coral atolls whose highest point is just a few meters above sea level.’ ‘The tsunami swamped up to 40 percent of the Maldives, an Indian Ocean string of 1,192 coral atolls 480 km southwest of the southern tip of India.’ ‘Diving is generally within the atoll lagoons for the inexperienced, and outside the atolls on reef walls for the advanced.’ ‘Reefs are generally divided into three categories; the barrier reef, the atoll, and the fringing reef.’ ‘The main island, the Tarawa atoll, is only a few metres above sea level and houses around 40,000 people.’ ‘The Maldives include nearly 1,200 islands in 15 major atolls spanning approximately 470 miles to just south of the equator.’ ‘

All the islands were formed by volcanic activity and can be divided into atolls and high islands.’ ‘The northern islands are coral atolls that have formed over ancient sunken volcanoes and are characterized by outer reefs surrounding a lagoon.’ Synonyms Maldives Islands My Maldives / Maldives Maldives Islands Paradise awaits you… If your idea of paradise is a pristine tropical island with swaying palm trees and pure white beaches surrounded by crystalline lagoons of varying shades of blue – then the Maldives Islands will definitely fit the bill.

Indeed, it is not without reason that the Maldives has been described as ‘(the) flower of the Indies’ by Marco Polo and ‘one of the wonders of the world’ by Ibn Batuta. It is no wonder that a large percentage of tourists who come to the Maldives are repeat visitors – people who came once and fell so in love with the place that they simple had to come again. The beauty of Maldives is indeed addictive. Once you sample the heady mixture of secluded serenity, thrilling water sports activities, soothing spas, relaxing beaches all wrapped in the luxurious comfort of modern amenities – you are bound to want the experience again. Sunny, unique and unspoiled, the islands of Maldives offers you sunshine, no matter what time of the year you decide to visit the Maldives – islands that are truly heaven on Earth. Maldives Atolls Maldives Islands is an archipelago comprising 1,190 low-lying coral islands scattered across the equator, in groups of 26 naturally occurring atolls which are divided into 20 for administrative purposes.

The atolls of Maldives are in fact part of a greater structure known as the Laccadives-Chagos Ridge, which stretches over 2000 kilometres. The islands of Maldives are very low lying with the highest point at approximately 8 feet above sea level. ‘Faru’ or ring-shaped reef structures form the atolls and these provide natural defense against wind and wave action, on the delicate islands. An indication of the perfection of Maldives atoll structure is the fact that the word ‘atoll’ in the English Language – meaning ‘ring-shaped coral reef enclosing a lagoon’, is a borrowing from the Maldivian language ‘Dhivehi’ . Of the more than 2000 tropical islands that make the paradise that is Maldives, only about 200 are inhabited. Of the remaining islands about a 100 have been developed into exotic resort islands that offer tourists their own hideaway – hidden away from all the hectic hustle and bustle of city life.

The capital of Maldives – Malé, the seat of government and the centre of trade, commerce, business, health and education, is located in the middle of the atoll chain, a small island buzzing with the sounds and activities of more than 150,000 people which is more than one third of the population. Malé is perhaps the smallest urban capital in the whole world. Where is Maldives The Maldives lies between latitudes 4 degree 17 North and longitudes 73 degree 50 East – a position where there is an abundance of sun all throughout the year, every year. The Maldives has always been a popular destination for travelers, especially seafarers because of its prime position en route to many trade destinations. The total area of 90,000 square kilometers over which the islands of Maldives are spread, consists of sparkling sun-kissed beaches, palm-fringed islands, crystalline lagoons studded with multi-coloured corals and warm, azure seas with exotic marine life – a mesmerizing mixture that remains the same throughout the year, continue to enthrall visitors from far and wide.

Maldives Microdocs: Types of Reefs Summary Tiny coral polyps build the massive structure of the reef. There are 4 main types of coral reef: fringing reef; barrier reef; atoll; and patch reef. As reefs mature, they can develop from fringing reefs to barrier reefs to atolls Building a reef Coral reefs are underwater rock outcrops covered by a thin layer of living coral polyps. These outcrops can be huge, sometimes over a kilometer (1 km = 0.7 miles) thick and hundreds of kilometers in length. But the coral polyps that build these massive structures form a layer only a few millimeters thick (1 mm = approximately 1/32"). Reef-building coral polyps live in a protective shell made from calcium carbonate (CaCO3), and as they divide and grow they form colonies. These colonies form the basic structure of the reef, helped by other organisms, like coralline algae. Building a reef is a slow process because the coral that form reefs grow about 0.3 - 2 cm (5/16 -13/16") each year.

It is estimated that coral polyps need about 10 000 years to form a reef , and 100 000 to 30 million years to build a fully mature reef. The 4 kinds of reef Polyps are only able to build a reef with the help of single-celled zooxanthellae algae. Polyps provide zooxanthellae with nutrients and shelter, and receive food in return. Zooxanthellae algae require sunlight for photosynthesis, and coral reefs usually begin to form in clear, shallow waters near land because water gradually filters out sunlight with depth. This relationship with land is used to categorize the different types of coral reef. 4 main types of reef exist: Fringing Reef This is the most common type of reef. They are located very close to land, and often form a shallow lagoon between the beach and the main body of the reef. images originally from USGS ( ) Barrier Reef This type of reef resembles a fringing reef, but they are located further from the shore and can be much bigger than fringing reefs.

For example, the Great Barrier Reef in Australia lies 300 – 1000m (328 - 1093 yards) from shore, and 2000km (1243 miles) long images originally from USGS ( ) Atoll These circular or horseshoe-shaped reefs encircle a lagoon. No apparent landmass is normally associated with an atoll. images originally from USGS ( ) Patch Reef These outcrops of coral usually lie within a lagoon. How to make an atoll Fringing reefs, barrier reefs and atolls are thought to represent stages in coral reef formation. Charles Darwin first proposed this theory of coral reef formation in 1842. Step 1: A fringing reef forms first, and starts growing in the shallow waters close to a tropical island. Step 2: Over time, the island subsides and the reef grows outwards, and the distance between the land and the reef increases. The fringing reef develops into a barrier reef. Step 3: If the island completely subsides, all that is left is the reef. The reef retains the approximate shape of the island it grew around, forming a ring enclosing a lagoon.

Darwin speculated that underneath each lagoon should be a bed rock base – the remains of the original island. Subsequent drilling into atolls proved this prediction true. Reefs require very similar conditions to develop and are subject to similar forces from the open ocean. This means that similar types of reefs form under the same conditions even if they are on opposite sides of the world. References Achituv, Y. & Dubinsky, Z. (1990). Evolution and Zoogeography of Coral Reefs. In Ecosystems of the World: 25 Coral Reefs. Dubinsky, Z. (ed.). Elsevier, New York. Anderson, G. (2003). Coral reef formation. MarineBio.net. Retrieved 5 September 2008 from Birkeland, C. (1997). Introduction. In Life and Death of Coral Reefs. Birkeland, C. (ed.). Chapman and Hall, New York. Darwin, C. (1842). The structure and distribution of coral reefs. [Reprint by University of California Press, Berkeley 1962] Hatcher, B.G. (1997).

Organic Production and Decomposition. In Life and Death of Coral Reefs. Birkeland, C. (ed.). Chapman and Hall, New York. NOAA. (2008, March 25). How do coral Reefs form? NOAA National Ocean Service Education. Retrieved March 25 2008 from Wikipedia. (2008, March 25). Coral Reef. Wikipedia. Retrieved March 25, 2008, from Wright, D. & Duncan, B. (2007, June 4). OC/GEO 103 Lecture - Ocean Habitats - Coral Reefs. Department of Geosciences, Oregon State University. Retrieved March 26, 2008, from All content property of microdocs project. Last updated April 11, 2012.

Question: What name is given to a ring shaped reef, enclosing a lagoon?
Answer: AN ATOLL