Misplaced Pages

#934065

36-794: List of atolls and isolated islands in the chain: The Rālik Chain is home to the Rālik dialect (or western dialect) of the Marshallese language. It is mutually intelligible with the Ratak dialect (or eastern dialect) located on the Ratak Chain . The two dialects differ mainly in lexicon and in certain regular phonological reflexes. This Marshall Islands location article is a stub . You can help Misplaced Pages by expanding it . Atoll An atoll ( / ˈ æ t . ɒ l , - ɔː l , - oʊ l , ə ˈ t ɒ l , - ˈ t ɔː l , - ˈ t oʊ l / )

72-508: 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

108-627: A 989,842-square-kilometre (382,180 sq mi) protected area was planned in the Coral Sea. The Supreme Court of Norfolk Island has jurisdiction over the islands; however, the laws of the Australian Capital Territory apply. The territory's FIPS 10-4 code is CR, whereas ISO 3166 includes it in Australia (AU). In June 2004, a symbolic political protest run by gay rights activists based in Australia, declared

144-414: 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 the island again, the rim provides

180-637: A group of small and mostly uninhabited tropical islands and reefs in the Coral Sea , north-east of Queensland , Australia. The only inhabited island is Willis Island . The territory covers 780,000 km (301,160 sq mi), most of which is ocean, extending east and south from the outer edge of the Great Barrier Reef and includes Heralds Beacon Island, Osprey Reef , the Willis Group and fifteen other reef/island groups. Cato Island

216-861: 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

252-510: 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

288-442: 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

324-525: 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

360-618: A wide range of size, from a few kilometres in diameter to perhaps the second largest atoll in the world by total area (including lagoon ): Lihou Reef , with a lagoon size of 100 by 30 kilometres (62 by 19 miles) and an area of 2,500 square kilometres (970 square miles), which compares to a combined land area of the 18 individual islets of only 0.91 square kilometres (0.35 square miles). The islands are all very low. The Willis Islets are important nesting areas for birds and turtles but contain negligible natural resources. They comprise less than three square kilometres (1.2 square miles) of land. There

396-496: Is a ring-shaped island, including a coral rim that encircles a lagoon . There may be coral islands or cays on the rim. Atolls are located in warm tropical or subtropical parts of the oceans and seas where corals can develop. Most of the approximately 440 atolls in the world are in the Pacific Ocean . Two different, well-cited models, the subsidence model and the antecedent karst model, have been used to explain

SECTION 10

#1732772007935

432-442: 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 the island or rising oceans). An alternative model for

468-622: Is no port or harbour, only offshore anchorage. Most of the atolls fall into two groups, while Mellish Reef to the east, and Middleton Reef and Elizabeth Reef to the south are grouped separately: The atolls of the Northwestern Group, except Osprey Reef and Shark Reef in the north, and Marion Reef in the south, are located on the Coral Sea Plateau (Queensland Plateau), a contiguous area of depths less than 1000 m. The Nature Reserves were created to protect wildlife in

504-690: Is the highest point in the Territory. The Coral Sea Islands were first charted in 1803. In the 1870s and 1880s the islands were mined for guano but the absence of a reliable supply of fresh water prevented long-term habitation. The Coral Sea Islands became an Australian external territory in 1969 by the Coral Sea Islands Act and extended in 1997 to include Elizabeth Reef and Middleton Reef nearly 800 km further south. The two latter reefs are much closer to Lord Howe Island , New South Wales , (about 150 km (93 mi)) than to

540-853: 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

576-606: 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

612-619: The Coral Sea Islands to be a sovereign micronation . On 17 November 2017 the same group declared the kingdom to be 'dissolved', following the results of the Australian Marriage Law Postal Survey . There are about 30 separate reefs and atolls , twelve being wholly submerged or drying only during low tide, and 18 others with a total of about 51 islets and cays (18 alone on the atoll Lihou Reef ), some of which are vegetated. The atolls exhibit

648-519: 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

684-520: 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

720-417: 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

756-416: 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 the ocean. As the volcanic island subsides, the coral fringing reef becomes a barrier reef that

SECTION 20

#1732772007935

792-436: 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

828-561: 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,

864-472: 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

900-458: The isles and reefs, and claims a 200-nautical-mile (370 km) exclusive fishing zone. There is no economic activity (except for a significant but as yet unquantified charter fishing and diving industry), and only a staff of three or four people to run the meteorological station on Willis Island (South Islet), established in 1921. In November 2011, the Australian government announced that

936-412: 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

972-412: 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 the flat surface of coral reef, it is exposed to the atmosphere as

1008-569: The respective areas of the territory; together they form the Coral Sea Reserves Ramsar Site . Elizabeth and Middleton reefs, together with reefs around Lord Howe Island ( New South Wales ) 150 km to the south, are regarded as the southernmost coral reefs in the world. Their location, where tropical and temperate ocean currents meet, contributes to an unusually diverse assemblage of marine species. These mostly submerged atolls which dry only during low tide were added to

1044-563: The southernmost island of the rest of the territory, Cato Island. The islands, cays and reefs of the Great Barrier Reef are not part of the territory, belonging to Queensland instead. The outer edge of the Great Barrier Reef is the boundary between Queensland and the Coral Sea Islands Territory. The territory is a possession or external territory of Australia , administered from Canberra . Previously it

1080-478: 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

1116-696: 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

Ralik - Misplaced Pages Continue

1152-444: 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]

1188-528: The territory only in 1989. They are located on the Lord Howe Rise . Already on 23 December 1987, they were protected as the Elizabeth and Middleton Reefs Marine National Park Reserve , which has an area of 1,880 km . Automatic, unmanned weather stations are located on the following reefs or atolls: Lighthouses are located on following reefs or islands: Willis Island, the only inhabited island, has

1224-756: 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

1260-737: Was administered by the Attorney-General's Department and the Department of Transport and Regional Services . It is the only external territory not created by transfer from the United Kingdom or by the mandate of the United Nations. Defence is the responsibility of Australia, and the territory is visited regularly by the Royal Australian Navy . Australia maintains automatic weather stations on many of

1296-477: 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. Coral Sea Islands The Coral Sea Islands Territory is an external territory of Australia which comprises

#934065