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38-625: Peros Banhos , Pedro dos Banhos or Baixos de Pêro dos Banhos in old maps, is a formerly inhabited atoll in the Chagos Archipelago of the British Indian Ocean Territory , also claimed by Mauritius . Île Yeye , located at the northeastern corner of the atoll, is the island of the Chagos Archipelago that is closest to the Maldives . The atoll has a total area of 503 km (194 sq mi), but

76-508: A reef knoll refers to the elevated remains of an ancient atoll within a limestone region, appearing as a hill. The second largest atoll by dry land area is Aldabra , with 155 km (60 sq mi). Huvadhu Atoll , situated in the southern region of the Maldives, holds the distinction of being the largest atoll based on the sheer number of islands it comprises, with a total of 255 individual islands. In 1842, Charles Darwin explained

114-485: A land area of only 9.6 km (3.7 sq mi), made up by some 32 islets. 490 km (189 sq mi), most of the remaining surface is occupied by the lagoon, which is connected to the open sea and the reef flat . Peros Banhos is a medium-sized coralline atoll circled by a regular coral reef , similar to those in the neighboring Maldives . The diameter of the lagoon, known as Baie de Peros Banhos in French,

152-793: A ring-shaped ribbon reef enclosing a lagoon". There are approximately 440 atolls in the world. Most of the world's atolls are in the Pacific Ocean (with concentrations in the Caroline Islands , the Coral Sea Islands , the Marshall Islands , the Tuamotu Islands , Kiribati , Tokelau , and Tuvalu ) and the Indian Ocean (the Chagos Archipelago , Lakshadweep , the atolls of the Maldives , and

190-442: A very different origin of formation. In most cases, the land area of an atoll is very small in comparison to the total area. Atoll islands are low lying, with their elevations less than 5 metres (16 ft). Measured by total area, Lifou (1,146 km , 442 sq mi) is the largest raised coral atoll of the world, followed by Rennell Island (660 km , 250 sq mi). More sources, however, list Kiritimati as

228-525: A volcanic island in the tropical sea will grow upward as the island subsides (sinks), becoming an "almost atoll", or barrier reef island, as typified by an island such as Aitutaki in the Cook Islands, and Bora Bora and others in the Society Islands. The fringing reef becomes a barrier reef for the reason that the outer part of the reef maintains itself near sea level through biotic growth, while

266-637: Is a French-based creole that was still spoken in 1994 by the 1,800 or so Chagossians , the former inhabitants of the Chagos Archipelago evicted in the early 1970s. Ilwa is a variety of Mauritian Creole with influences from Seychellois Creole . It is currently spoken mainly in Mauritius and the Seychelles . There is also a small minority community speaking the language in the United Kingdom . Papen, Robert A. 1978. The French-based Creoles of

304-426: Is closest to the Maldives . The distance between Île Yeye and Gan Island ( Addu Atoll ) is 523 kilometres (325 mi). There have been some changes in the geography of this atoll since the first maps were published in the mid-19th century. Île St. Brandon, which was covered with coconut trees when the first survey of this atoll was done, is now just a sandbank. On the other hand, in the western rim of Peros Banhos,

342-543: Is in accordance with international law." The part of the atoll east of a line drawn between the easternmost point of land on Moresby Island (north) and the easternmost point of land on Fouquet Island (south) fall within the Peros Banhos Atoll Strict Nature Reserve . Entry into this and into the other Strict Nature Reserves , and within 200 metres (660 ft) of the islands therein is prohibited and activities are clearly proscribed by

380-501: Is just above 20 km. The circling reef is sunken on its southeastern rim. All islands are flat and sandy and the largest ones are covered with coconut trees. The largest and most important island in the group is Île du Coin . It was home to the Perch Settlement from where the coconut plantations of the atoll were run. This island was the main port of the atoll and had a jetty to load and unload merchandise. Île du Coin

418-604: The British Indian Ocean Territory . It has been identified as an Important Bird Area by BirdLife International because of its significance as a breeding site for sooty terns , of which 14,000 pairs were recorded in a 2004 survey. Yachtsmen are advised not to even anchor within the limits of the Peros Banhos Atoll Strict Nature Reserve. With some 32 islets, the Peros Banhos Atoll encompasses about half of all islands in

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456-853: The Outer Islands of Seychelles ). In addition, Indonesia also has several atolls spread across the archipelago, such as in the Thousand Islands , Taka Bonerate Islands , and atolls in the Raja Ampat Islands . The Atlantic Ocean has no large groups of atolls, other than eight atolls east of Nicaragua that belong to the Colombian department of San Andres and Providencia in the Caribbean. Reef-building corals will thrive only in warm tropical and subtropical waters of oceans and seas, and therefore atolls are found only in

494-606: The Royal Society of London carried out drilling on Funafuti atoll in Tuvalu for the purpose of investigating the formation of coral reefs . They wanted to determine whether traces of shallow water organisms could be found at depth in the coral of Pacific atolls. This investigation followed the work on the structure and distribution of coral reefs conducted by Charles Darwin in the Pacific. The first expedition in 1896

532-612: The Chagos Archipelago . The individual islands and islets are listed clockwise, starting in the south: Passe de l'Île Poule is also called Passe Elisabeth on older maps. The islands in the eastern part are part of the Peros Banhos Strict Nature Reserve, except Île De La Passe and Moresby Island. 5°20′S 71°51′E  /  5.333°S 71.850°E  / -5.333; 71.850 Atoll Two different, well-cited models,

570-519: The Equator is Aranuka of Kiribati. Its southern tip is just 13 km (8 mi) north of the Equator. Bermuda is sometimes claimed as the "northernmost atoll" at a latitude of 32°18′ N. At this latitude, coral reefs would not develop without the warming waters of the Gulf Stream . However, Bermuda is termed a pseudo-atoll because its general form, while resembling that of an atoll, has

608-520: The antecedent karst model as they found that the morphology of modern atolls are independent of any influence of an underlying submerged and buried island and are not rooted to an initial fringing reef/barrier reef attached to a slowly subsiding volcanic edifice. In fact, the Neogene reefs underlying the studied modern atolls overlie and completely bury the subsided island are all non-atoll, flat-topped reefs. In fact, they found that atolls did not form doing

646-473: The birds lasted the castaways survived, but they began to die in great numbers after having eaten most of the bird population. According to Manoel Rangel there was drinking water to be found by digging shallow wells in the sand. Also many turtles came to lay eggs on the beach of that island. Since 1756 Île du Coin was home to a population of up to 500 people. Most of the inhabitants, the Ilois , were workers in

684-512: The coconut plantations and in the oil-producing industry. The Ilois were Christian and there were churches and primary schools in Peros Banhos before the local population was moved away. Their language was a Creole version of French, known as Chagossian Creole . There is a small bushy island called Île Diable on the NW of the atoll. Moresby Island , at the northern end of Peros Banhos Atoll

722-417: The creation of coral atolls in the southern Pacific Ocean based upon observations made during a five-year voyage aboard HMS Beagle from 1831 to 1836. Darwin's explanation suggests that several tropical island types: from high volcanic island, through barrier reef island, to atoll, represented a sequence of gradual subsidence of what started as an oceanic volcano. He reasoned that a fringing coral reef surrounding

760-436: The direct result of the interaction between subsidence and preferential karst dissolution that occurred in the interior of flat topped coral reefs during exposure during glacial lowstands of sea level. The elevated rims along an island created by this preferential karst dissolution become the sites of coral growth and islands of atolls when flooded during interglacial highstands. The research of A. W. Droxler and others supports

798-561: The dolomitization of calcite and aragonite within them. They are the evaporative, seepage-reflux, mixing-zone, burial, and seawater models. Although the origin of replacement dolomites remains problematic and controversial, it is generally accepted that seawater was the source of magnesium for dolomitization and the fluid in which calcite was dolomitized to form the dolomites found within atolls. Various processes have been invoked to drive large amounts of seawater through an atoll in order for dolomitization to occur. In 1896, 1897 and 1898,

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836-446: The flat surface of coral reef, it is exposed to the atmosphere as a flat topped island which is dissolved by rainfall to form limestone karst . Because of hydrologic properties of this karst, the rate of dissolution of the exposed coral is lowest along its rim and the rate of dissolution increases inward to its maximum at the center of the island. As a result, a saucer shaped island with a raised rim forms. When relative sea level submerges

874-472: The inner part of the reef falls behind, becoming a lagoon because conditions are less favorable for the coral and calcareous algae responsible for most reef growth. In time, subsidence carries the old volcano below the ocean surface and the barrier reef remains. At this point, the island has become an atoll. As formulated by J. E. Hoffmeister, F. S. McNeil, E. G. Prudy, and others, the antecedent karst model argues that atolls are Pleistocene features that are

912-490: The island again, the rim provides a rocky core on which coral grow again to form the islands of an atoll and the flooded bottom of the saucer forms the lagoon within them. The word atoll comes from the Dhivehi word atholhu ( އަތޮޅު , pronounced [ˈat̪oɭu] ). Dhivehi is an Indo-Aryan language spoken in the Maldives . The word's first recorded English use was in 1625 as atollon . Charles Darwin coined

950-482: The island north of Île Verte was only a small sandbank at the time of Commander Robert Moresby 's Survey in 1837, but now it is a medium-sized island covered with vegetation. Peros Banhos was discovered in 1513 by Portuguese navigator Afonso de Albuquerque . The name of this atoll derives from "Pêro dos Banhos", the name of another Portuguese navigator who died there after his ship ran aground on this atoll. The earliest and most interesting description of Peros Banhos

988-403: The island or rising oceans). An alternative model for the origin of atolls is called the antecedent karst model. In the antecedent karst model, the first step in the formation of an atoll is the development of a flat top, mound-like coral reef during the subsidence of an oceanic island of either volcanic or nonvolcanic origin below sea level. Then, when relative sea level drops below the level of

1026-579: The islands have been investigated as a possible location for resettlement, although access is currently prohibited. In February 2022, exiled islanders made their first unsupervised visit to the island, following international court rulings and a majority vote in the UN General Assembly . Prime Minister of Mauritius, Pravind Jugnauth , said this was not to embarrass the UK, but "merely an exercise of our sovereignty over part of our territory and that

1064-412: The largest atoll in the world in terms of land area. It is also a raised coral atoll (321 km , 124 sq mi land area; according to other sources even 575 km , 222 sq mi), 160 km (62 sq mi) main lagoon, 168 km (65 sq mi) other lagoons (according to other sources 319 km , 123 sq mi total lagoon size). The geological formation known as

1102-482: The ocean. As the volcanic island subsides, the coral fringing reef becomes a barrier reef that is detached from the island. Eventually, reef and the small coral islets on top of it are all that is left of the original island, and a lagoon has taken the place of the former volcano. The lagoon is not the former volcanic crater. For the atoll to persist, the coral reef must be maintained at the sea surface, with coral growth matching any relative change in sea level (sinking of

1140-399: The subsidence model and the antecedent karst model, have been used to explain the development of atolls. According to Charles Darwin 's subsidence model, the formation of an atoll is explained by the sinking of a volcanic island around which a coral fringing reef has formed. Over geologic time, the volcanic island becomes extinct and eroded as it subsides completely beneath the surface of

1178-478: The subsidence of an island until MIS-11, Mid-Brunhes, long after the many the former islands had been completely submerged and buried by flat topped reefs during the Neogene. Atolls are the product of the growth of tropical marine organisms, and so these islands are found only in warm tropical waters. Volcanic islands located beyond the warm water temperature requirements of hermatypic (reef-building) organisms become seamounts as they subside, and are eroded away at

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1216-696: The surface. An island that is located where the ocean water temperatures are just sufficiently warm for upward reef growth to keep pace with the rate of subsidence is said to be at the Darwin Point . Islands in colder, more polar regions evolve toward seamounts or guyots ; warmer, more equatorial islands evolve toward atolls, for example Kure Atoll . However, ancient atolls during the Mesozoic appear to exhibit different growth and evolution patterns. Coral atolls are important as sites where dolomitization of calcite occurs. Several models have been proposed for

1254-444: The term in his monograph, The Structure and Distribution of Coral Reefs . He recognized the word's indigenous origin and defined it as a "circular group of coral islets", synonymously with "lagoon-island". More modern definitions of atoll describe them as "annular reefs enclosing a lagoon in which there are no promontories other than reefs and islets composed of reef detritus " or "in an exclusively morphological sense, [as]

1292-756: The tropics and subtropics. The northernmost atoll in the world is Kure Atoll at 28°25′ N, along with other atolls of the Northwestern Hawaiian Islands . The southernmost atolls in the world are Elizabeth Reef at 29°57′ S, and nearby Middleton Reef at 29°27′ S, in the Tasman Sea , both of which are part of the Coral Sea Islands Territory. The next southerly atoll is Ducie Island in the Pitcairn Islands Group, at 24°41′ S. The atoll closest to

1330-496: Was led by Professor William Johnson Sollas of the University of Oxford . Geologists included Walter George Woolnough and Edgeworth David of the University of Sydney . Professor Edgeworth David led the expedition in 1897. The third expedition in 1898 was led by Alfred Edmund Finckh. Chagossian Creole Chagossian creole also known as Chagossian Kreol (also créole îlois , kreol Ilwa , or just Ilwa )

1368-605: Was named after Robert Moresby , a British hydrographer who made the first accurate survey of the Chagos Archipelago in 1837. After Moresby's survey, the first detailed map of Peros Banhos Atoll was published by the Hydrographic Service of the Indian Navy . In 1970, the entire population of Peros Banhos Atoll was expelled by the British Government and sent to live in Mauritius . More recently,

1406-457: Was the only island that was settled permanently in Peros Banhos. Other important islands in the atoll that had buildings on them and were also occasionally inhabited were Grande Soeur , Île Diamant , Île Manoël and Île Pierre . All these islands were part of the former coconut plantation run from Île du Coin. Île Yeye , at the northeastern corner of the atoll, is the island of the Chagos that

1444-620: Was written by Manoel Rangel in «A Tragédia dos Baixos de Pero dos Banhos» . He was a castaway from the Portuguese ship Conceição under captain Francisco Nobre that ran aground and was smashed on the Peros Banhos reefs in 1556. 165 survivors were left on a flat sandy island of Peros Banhos before coconut trees were there; among them were two women and five Catholic priests. Rangel mentions that there were weeds and grasses and that about ten thousand birds lived on that Island. While

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