"Gnaviyani Atoll Gnaviyani Atoll is one of the administrative divisions of the Maldives corresponding to the natural atoll, Fuvahmulah. Surfacewise this is the smallest administrative unit in the Maldives, situated in the Equatorial Channel (Addu - Mulah Kandu) between Huvadhu Atoll and Addu Atoll. The atoll of Fuvahmulah corresponding to this administrative division is the 25th natural atoll of the Maldives. Some people due to lack of knowledge or as part of a prevailing misconception erroneously mention that Fuvahmulah is not an atoll. An island of coral that encircles a lagoon partially or completely is what we call an atoll."
"island of Surtsey, which was formed in 1963. An atoll is an island formed from a coral reef that has grown on an eroded and submerged volcanic island. The reef rises to the surface of the water and forms a new island. Atolls are typically ring-shaped with a central lagoon. Examples are the Line Islands in the Pacific and the Maldives in the Indian Ocean. Approximately 45,000 tropical islands with an area of at least exist. Examples formed from coral reefs include Maldives, Tonga, Samoa, Nauru, and Polynesia. Granite islands include Seychelles and Tioman and volcanic islands such as Saint"
"from fringing reefs around volcanic islands. Over time, the island erodes away and sinks below sea level. Atolls may also be formed by the sinking of the seabed or rising of the sea level. A ring of reefs results, which enclose a lagoon. Atolls are numerous in the South Pacific, where they usually occur in mid-ocean, for example, in the Caroline Islands, the Cook Islands, French Polynesia, the Marshall Islands and Micronesia. Atolls are found in the Indian Ocean, for example, in the Maldives, the Chagos Islands, the Seychelles and around Cocos Island. The entire Maldives consist of 26 atolls."
"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. Atolls are the product of the growth of tropical marine organisms, and so these islands are only found 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 the surface. An island that is located where the ocean water temperatures are just"
"in modern atolls and a number of different processes have been invoked to explain it, such as geothermally driven convection of seawater. Dissolved fossils and traces of animal burrows are found in some rock sequences with bioturbation traces widespread. Barite needles, calcretes, cementation forms that developed under the influence of freshwater, desiccation cracks and ferromanganese occurrences as dendrites have also been found. Organic materials have been found in rock samples from Resolution Guyot and appear to be mainly of marine origin. However, some of the organic matter comes from microbial mats and vegetated islands, including wood and plant fragments. Clays"
"(atoll with four islets). The Pitcairn Islands were formed by a centre of upwelling magma called the Pitcairn hotspot. The only permanently inhabited island, Pitcairn, is accessible only by boat through Bounty Bay. Henderson Island, covering about 86% of the territory's total land area and supporting a rich variety of animals in its nearly inaccessible interior, is also capable of supporting a small human population despite its scarce fresh water, but access is difficult, owing to its outer shores being steep limestone cliffs covered by sharp coral. In 1988, this island was designated as a UNESCO World Heritage site. The"
"atoll has, besides the four larger islands, some 40 smaller islands and rocks, all inside the lagoon, as well as a few very small islets at the West Channels between Grand Terre Island and Picard Islands, the largest of those being Îlot Magnan. More Islands (unspecified location, but sizes are included under ""Other Islands"": The atoll reflects both fossil and geomorphological features, the former is the source of the biodiversity seen today. The atoll is made of reef limestone of Pleistocene age (with irregular coral formations called ""champignon"", made up of two layers of varying stages of crystallization ) and"
"continued erosion or subsidence must be at a rate slow enough to permit reef growth upwards and outwards to replace the lost height. The word ""atoll"" comes from the Dhivehi (an Indo-Aryan language spoken on the Maldive Islands) word ""atholhu"" (Dhivehi: , ), meaning an administrative subdivision. Its first recorded use in English was in 1625 as ""atollon"". Charles Darwin recognized its indigenous origin and coined, in his ""The Structure and Distribution of Coral Reefs"", the definition of atolls as ""circular groups of coral islets"" that is synonymous with ""lagoon-island"". More modern definitions of ""atoll"" describe them as ""annular reefs"
"of rock to the ocean surface and created the islands of the Lesser and Greater Antilles, including Bonaire. As the seabed rose a vast coral reef grew on what is now dry land. These corals were eventually exposed to air and perished, becoming surface limestone deposits over the millennia. Vast amounts of coral skeletons may be seen along the shoreline and across the interior of Bonaire. The island is essentially a coral reef that has been geologically pushed up and out of the sea. This also resulted in the natural fringing reef system seen today, in which the coral formations"
"Coral island A coral island is a type of island formed from coral detritus and associated organic material. They occur in tropical and sub-tropical areas, typically as part of coral reefs which have grown to cover a far larger area under the sea. Coral reefs are some of the oldest ecosystems on the planet. Over geological time forming massive reefs made of limestone. The reef environment supports more plant and animal species than any other habitat. Coral reefs are vital for life for multiple aspects some of which include structure, ecology, and nutrient cycles which all support biodiversity in the"
"pseudo-atoll, has two small islands, which are gradually undergoing coastal erosion, and appear as just small sandstone ridges exposed only at low tide. The underwater banks extend over north-south and east-west and occupy a total area of about . With a shallow coral ring, it appears as an incomplete atoll. To the west of the coral ring, however, it is deep. North Island ( fr. Île du Nord ) is small and flat with an area of . It has a derelict automatic lighthouse on the north point. and is occasionally visited by tourists in charter yachts. It was formed"
"Microatoll A microatoll is a circular colony of coral, dead on the top but living around the perimeter. Growth is mainly lateral, as upward growth is limited by exposure to air. Microatolls may be up to in diameter. They are named for their resemblance to island atolls formed during the subsidence of volcanic islands, as originally suggested by Darwin (1842). They act as natural recorders of sea level, which allows the monitoring of sea level changes in response to global warming. They have also been used to quantify and date changes in relative sea level in seismically active areas, and"
"or fragments of continents, Oceania is composed mostly of volcanic high islands and coral atolls that arose from the sea in geologically recent times, many of them in the Pleistocene. They were created either by hotspot volcanism, or as island arcs pushed upward by the collision and subduction of tectonic plates. The islands range from tiny islets, sea stacks and coral atolls to large mountainous islands, like Hawaii and Fiji. The climate of Oceania's islands is tropical or subtropical, and range from humid to seasonally dry. Wetter parts of the islands are covered by Tropical and subtropical moist broadleaf forests,"
"are small with low elevation above sea level. Thus they are at threat from storms and rising sea levels. Coral island A coral island is a type of island formed from coral detritus and associated organic material. They occur in tropical and sub-tropical areas, typically as part of coral reefs which have grown to cover a far larger area under the sea. Coral reefs are some of the oldest ecosystems on the planet. Over geological time forming massive reefs made of limestone. The reef environment supports more plant and animal species than any other habitat. Coral reefs are vital for"
"Waialeale, and Niihau volcanoes are in this stage of development. Eventually, erosion and subsidence break the volcano down to sea level. At this point, the volcano becomes an atoll, with a ring of coral and sand islands surrounding a lagoon. All the Hawaiian islands west of the Gardner Pinnacles in the Northwestern Hawaiian Islands are in this stage. Atolls are the product of the growth of tropical marine organisms, so these islands are only found in warm tropical waters. Eventually, the Pacific Plate carries the volcanic atoll into waters too cold for these marine organisms to maintain a reef by"
"Floating island A floating island is a mass of floating aquatic plants, mud, and peat ranging in thickness from several centimetres to a few metres. Floating islands are a common natural phenomenon that are found in many parts of the world. They exist less commonly as a man-made phenomenon. Floating islands are generally found on marshlands, lakes, and similar wetland locations, and can be many hectares in size. Sometimes referred to as ""tussocks"", ""floatons"", or ""suds"", natural floating islands are composed of vegetation growing on a buoyant mat of plant roots or other organic detritus. Some cenotes in northern Mexico"
"containing air voids. Growth media include coconut fibre; mats made of polyester or recycled PET bottles; synthetic geotechnical mat; jute; soil; and sand. Floating island A floating island is a mass of floating aquatic plants, mud, and peat ranging in thickness from several centimetres to a few metres. Floating islands are a common natural phenomenon that are found in many parts of the world. They exist less commonly as a man-made phenomenon. Floating islands are generally found on marshlands, lakes, and similar wetland locations, and can be many hectares in size. Sometimes referred to as ""tussocks"", ""floatons"", or ""suds"", natural"
"Atolls of the Maldives The Maldives are formed by a number of natural atolls plus atolls in the form of a few islands and isolated reefs today which form a pattern stretching from 7 degrees 10′ North to 0 degrees 45′ South. The Maldives is a long and narrow country formed by 26 natural atolls. Some atolls are in the form of a number of islands by time and in the form of isolated reefs, which could be classified as smaller atoll formations. All land above the surface in the Maldives is of coralline origin. The atolls of the Maldives"
"Artificial island An artificial island or man-made island is an island that has been constructed by people rather than formed by natural means. Artificial islands may vary in size from small islets reclaimed solely to support a single pillar of a building or structure, to those that support entire communities and cities. Early artificial islands included floating structures in still waters, or wooden or megalithic structures erected in shallow waters (e.g. crannógs and Nan Madol discussed below). In modern times artificial islands are usually formed by land reclamation, but some are formed by the incidental isolation of an existing piece"
"of relatively untouched natural beauty where a number of important animal species and some plant species thrive, along with remarkable land formations, and its process provides a unique spectacle of natural phenomena; Criterion (ix): The atoll is a superlative example of an oceanic island ecosystem in which evolutionary processes are active within a rich biota. The size and morphological diversity of the atoll has permitted the development of a variety of discrete insular communities with a high incidence of endemicity among the constituent species that are typical of island ecosystems. The natural processes take place with minimal human interference and"
"are some differences to present-day reef systems, many of these seamounts were formerly atolls, which today still exist. All these structures originally formed as volcanoes in the Mesozoic ocean. Fringing reefs may have developed on the volcanoes, which then became barrier reefs as the volcano subsided and turned into an atoll, and which surround a lagoon or tidal flat. The crust underneath these seamounts tends to subside as it cools, and thus the islands and seamounts sink. Continued subsidence balanced by upward growth of the reefs led to the formation of thick carbonate platforms. Sometimes volcanic activity continued even after"
"become drowned, without sufficient light. Coral reefs are found in the deep sea away from continental shelves, around oceanic islands and atolls. The majority of these islands are volcanic in origin. Others have tectonic origins where plate movements lifted the deep ocean floor. In ""The Structure and Distribution of Coral Reefs"", Charles Darwin set out his theory of the formation of atoll reefs, an idea he conceived during the voyage of the ""Beagle"". He theorized that uplift and subsidence of the Earth's crust under the oceans formed the atolls. Darwin set out a sequence of three stages in atoll formation."
"top and usually the presence of corals and carbonate platforms. These structures originally formed as volcanoes in the Mesozoic Ocean. Fringing reefs may have developed on the volcanoes, which then were replaced by barrier reefs as the volcanoes subsided and turned into atolls. Continued subsidence balanced by upward growth of the reefs led to the formation of thick carbonate platforms. Volcanic activity can occur even after the formation of the atoll or atoll-like landforms, and during episodes where the platforms were lifted above sea level, erosional features such as channels and blue holes developed. The crust underneath these seamounts tends"
"barrier reef, they can form a linear arrangement. This is the case, for example, on the east coast of the Red Sea near Jeddah. In old platform reefs, the inner part can be so heavily eroded that it forms a pseudo-atoll. These can be distinguished from real atolls only by detailed investigation, possibly including core drilling. Some platform reefs of the Laccadives are U-shaped, due to wind and water flow. Atolls or atoll reefs are a more or less circular or continuous barrier reef that extends all the way around a lagoon without a central island. They are usually formed"
"made up of areas of seagrass and reef systems. Along with Edwards Island it is at the southern end of the Turquoise Coast islands nature reserve group, a chain of 40 islands spread over a distance of . The island was formed approximately 10,000 years ago after large fluctuations in sea levels caused erosion on large areas of the continental shelf during periods of glaciation. Large parallel sand dunes then formed and hardened into limestone, forming islands, most of which have been separated from the mainland for 6,500 years. The first European to discover and name the island was the"
"in oxygen isotope ratios in fossil microatolls have also been used to provide high-resolution proxy records for sea surface temperature over the last few thousand years. Microatoll A microatoll is a circular colony of coral, dead on the top but living around the perimeter. Growth is mainly lateral, as upward growth is limited by exposure to air. Microatolls may be up to in diameter. They are named for their resemblance to island atolls formed during the subsidence of volcanic islands, as originally suggested by Darwin (1842). They act as natural recorders of sea level, which allows the monitoring of sea"
"is located. Artificial islands can be built using natural materials (e.g., earth, rock, or sand) or artificial ones (e.g., concrete slabs or recycled waste). Sometimes natural islands are artificially enlarged, such as Vasilyevsky Island in the Russian city of St. Petersburg, which had its western shore extended westward by some 0.5 km in the construction of the Passenger Port of St. Petersburg. Artificial islands are sometimes built on pre-existing ""low-tide elevation,"" a naturally formed area of land which is surrounded by and above water at low tide but submerged at high tide. Legally these are not islands and have no"
"of land during canal construction (e.g. Donauinsel and Ko Kret), or flooding of valleys resulting in the tops of former knolls getting isolated by water (e.g. Barro Colorado Island). One of the world's largest artificial islands, René-Levasseur Island, was formed by the flooding of two adjacent reservoirs. Despite a popular image of modernity, artificial islands actually have a long history in many parts of the world, dating back to the reclaimed islands of Ancient Egyptian civilization, the Stilt crannogs of prehistoric Scotland and Ireland, the ceremonial centers of Nan Madol in Micronesia and the still extant floating islands of Lake"
"strip wide lies inland from the beach. Wake Island is a coral atoll with a coastline of just north of the Marshall Islands. It is an unorganized, unincorporated territory of the United States. Access to the island is restricted and all activities on the island are managed by the United States Air Force. The majority of the islands in the area are part of a coral atoll. Coral atolls begin as coral reefs that grow on the slopes of a central volcano. When the volcano sinks back down into the sea, the coral continues to grow, keeping the reef at"
"Atolls have developed in tropical waters when, after volcanos sink, coral growth results in reefs as evidenced by the Cook Islands. Coral reefs can develop into islands over a submerged extinct volcano following uplift as in Makatea and Rennell Island in the Solomon Archipelago which have steep coral cliffs over 100 metres high. The collision of two plates, resulting in subduction, have contributed to the emergence of the western Pacific arcs of volcanic islands. A new crust has emerged as the East Pacific Rise. In the northeastern Pacific margin there is a lateral shift, through the San Andreas Fault system,"
"the formation of the atoll or atoll-like structure, and during episodes where the platforms rose above sea level erosional features such as channels and blue holes developed. The formation of many such seamounts has been explained with the hotspot theory, which describes the formation of chains of volcanoes which get progressively older along the length of the chain, with an active volcano only at one end of the system. This volcano lies on a spot of the lithosphere heated from below; as the plate moves the volcano is moved away from the heat source and volcanic activity ceases, producing a"
"Sollerön Island in Siljan Lake, Sweden, and an unnamed island in Lake Karakul, Tajikistan, was also formed by meteor impact. The term floating island is sometimes used for accumulations of vegetation free-floating within a body of water. Due to the lack of currents and tides, these are more frequently found in lakes than in rivers or the open sea. Peaty masses of vegetable matter from shallow lake floors may rise due to the accumulation of gases during decomposition, and will often float for a considerable time, becoming ephemeral islands until the gas has dissipated enough for the vegetation to return"
"have developed on the volcanoes, which then became barrier reefs as the volcano subsided and turned into an atoll. The crust underneath these seamounts tends to subside as it cools, and thus the islands and seamounts sink. Continued subsidence balanced by upward growth of the reefs led to the formation of thick carbonate platforms. Sometimes volcanic activity continued even after the formation of the atoll or atoll-like structure, and during episodes where the carbonate platforms rose above sea level, erosional features such as channels and blue holes developed. The formation of many such seamounts has been explained with the hotspot"