Atoll definition. Geographical encyclopedia
atoll-coral structure in the form of a continuous or broken ring bordering a water basin - a lagoon. The ring of the atoll is formed by separate islands. Some of them have their own lagoon or are an incomplete ring that opens towards the main lagoon with a wide channel. Found only in the tropical zone. They can have different sizes, usually small, but some reach 50 km across. The underwater base of the atoll is usually the heights of the ocean floor of volcanic origin. The genesis of the atoll, according to Charles Darwin's hypothesis, is associated with the slow subsidence of a tropical island surrounded by a ring of barrier coral reef, which is gradually expanding with the construction of colonial corals. According to another concept, the formation of atolls occurs as a result of a rise in the level of the World Ocean as a result of the melting of cover glaciers, and not the subsidence of the bottom, as evidenced, in his opinion, by the same depths from which coral structures begin in different atolls. you are very demanding on the complex natural conditions: the temperature of air and water, the constancy of salinity and dynamics of ocean waters, their purity, etc. They are found mainly in the waters of the Pacific and Indian oceans.
Plan and vertical section of the atoll (along line AB)
View value Atoll in other dictionaries
Atoll- m. coral island with an open ring; an annular, lagoon ridge, an island, gradually carved out by the smallest skull-dwellers, with a lake or lagoon in the middle (lagoon........
Dahl's Explanatory Dictionary
Atoll- atoll, m. (Malay). Ring-shaped coral island.
Ushakov's Explanatory Dictionary
Atoll M.— 1. A coral island shaped like a ring (sometimes broken).
Explanatory Dictionary by Efremova
Atoll- -A; m. [English] atoll]. A ring-shaped coral island with a shallow lagoon inside (mainly in the Indian and Pacific oceans).
Kuznetsov's Explanatory Dictionary
Atoll- , a ring-shaped CORAL REEF surrounding a shallow LAGOON. The reef appears initially as the frame of an island slowly sinking into the water, usually volcanic........
Scientific and technical encyclopedic dictionary
Atoll- a coral structure in the form of a continuous or broken ring surrounding a shallow lagoon. The base for an atoll is usually the top of an underwater volcano.........
Large encyclopedic dictionary
Atoll
ato ll, atoll, husband. (Malay). Ring-shaped coral island.
Naval Dictionary
Atoll
a coral island in the form of a continuous or broken ring, rising several meters above sea level and surrounding a shallow (60-150 m) lagoon. Distributed in the tropical regions of the Pacific and Indian oceans and only in those places where warm currents do not pass.
Geomorphological dictionary-reference book
Atoll
(from Maldivian Atoll) - a ring coral reef, morphologically representing a narrow ridge with a closed (or semi-closed) lagoon inside. A. sizes are different. Some of them are up to 100 km in diameter (A. Menshikova in the Pacific Ocean), but more common are A. with a diameter of several kilometers to several tens of kilometers. There are A. raised (Nauru Island) and submerged (Robbie Bank) due to tectonic movements of their foundations. Most A. are concentrated in the Indo-Pacific tropical zone, but they are also known in the Atlantic, for example, in the Caribbean Sea, and off the coast of Brazil.
Tourist vocabulary
Atoll
(from Maldivian) a coral island or group of islands that looks like a continuous or discontinuous ring surrounding a lagoon. The individual islands that form the atoll are called motu.
Encyclopedic Dictionary
Atoll
a coral structure in the form of a continuous or broken ring surrounding a shallow lagoon. The base for an atoll is usually the top of an underwater volcano. Distributed in tropical latitudes of the Pacific and Indian oceans.
Ozhegov's Dictionary
AT ABOUT LL, A, m. Ring-shaped coral island.
What is an atoll? An atoll is a ring-shaped coral reef that partially or completely surrounds a lagoon. In other words, an atoll is a narrow piece of land that both borders and is surrounded by water. This is what distinguishes an atoll from an ordinary island. While an island is just a piece of land surrounded by water, an atoll contains a body of water within itself.
Another interesting thing about atolls is the fact that they are not actually made of soil, but of coral. The corals have to grow fast enough to replace parts of the atoll that are being destroyed by erosion in order for the atoll to remain intact. Because corals thrive only in warm waters, atolls can only be found in the tropics and subtropics. Hence, atolls are unique coral land masses consisting of crystal clear lagoon and spectacular colorful reefs overflowing with amazing marine life. Sounds exciting, doesn't it?!
Let's go on an amazing journey through the tropics. From the stunning Aitutaki Atoll in the Cook Islands to the otherworldly beauty of the atolls in the Maldives, we present to you the 25 most stunning atolls in the world.
25. Takapoto French Polynesia
Takapoto, measuring 20 by 7 kilometers, is an atoll located in the Tuamoto archipelago in French Polynesia. Discovered by Dutch navigator Jacob Le Maire in 1616, the atoll is currently home to approximately 380 people.
24. Aitutaki, Cook Islands
Aitutaki Atoll is home to approximately 2,000 people. It is the second most visited island in the Cook Islands. The atoll that the authorities saved from mass tourism, famous for its turquoise waters of the central lagoon and picturesque beaches, bordered by palm trees.
23. Ulithi, Caroline Islands
Ulithi, part of the Federated States of Micronesia, is an atoll made up of 40 islets surrounding one of the largest lagoons in the world. The atoll was the main staging area for the US Navy during World War II. Several sunken ships are still at the bottom of this lagoon.
22. Tubbataha Reef, Philippines
Tubbataha Reef, located in the center of the Sulu Sea, is a marine and bird sanctuary consisting of two large atolls - North and South Atoll. This protected area boasts amazing biodiversity and contains 75 percent of the known coral species and 40 percent of the reef fish species known to science.
21. Tarawa, Kiribati
Tarawa is an atoll and the capital of the Republic of Kiribati, located in the central part Pacific Ocean. Home to almost 60,000 people, the atoll boasts a wide reef teeming with fish and a large lagoon spanning more than 500 square kilometers.
20. Tikehau, French Polynesia
Tikehau, located 340 kilometers northeast of Tahiti in the Tuamotu Islands, is an oval-shaped atoll and tourist destination famous for pink sandy beaches, fringed by coconut palms and stunning marine fauna and flora.
19. Maafushi, Maldives
Maafushi, part of the Kaafu Atoll, is one of the inhabited islands in the Maldives. The atoll was heavily damaged by the tsunami in 2004, but quickly recovered. Currently, Maafushi boasts a thriving local economy based on fishing and tourism.
18. St. Francois Atoll, Seychelles
Saint Francois Atoll, consisting of the two islands of Saint Francois and Bijoutier, is an uninhabited atoll in the western Indian Ocean. The atoll is a habitat for numerous species of birds, including the common tern, the curlew, the turnstone, the tule and so on.
17. Rangiroa, French Polynesia
, one of the largest atolls in the world, consists of approximately 415 tiny islands and shoals, covering a total area of about 170 square kilometers. In the center of the atoll, there is a large lagoon where black pearl oysters are bred.
16. Palmyra Atoll, Equatorial North Pacific Ocean
Palmyra Atoll, located between Hawaii and American Samoa, is an unoccupied atoll consisting of an extensive reef, lagoons and 50 islets. The atoll is officially administered by the United States and is covered with coconut palms, scevola and pisonia trees.
15. Nukuoro Federated States Micronesia
Surrounding a lagoon 6 kilometers in diameter, Nukuoro is a remote atoll home to almost 400 people. There is no tourism on the island, except for occasional visits from passing sailing yachts.
14. Ontog Java Atoll, Solomon Islands
Ontong Java Atoll is sometimes also called Lord Howe Atoll. It is a large shoe-shaped atoll consisting of more than 120 low-lying islets. There are two large villages on the atoll - Luaniua and Pelau - where most of the atoll's population lives.
13. Nukumanu, Papua New Guinea
Nukumanu is a medium-sized atoll that is part of Papua New Guinea and located in the southwest Pacific Ocean, 4 degrees south of the equator. The atoll consists of 20 sandy islets surrounding a large lagoon.
12. Lihou Reef, Coral Sea Islands Territory
Lihou Reef, located in the Coral Sea, northeast of Queensland, Australia, is the second largest atoll in the world in terms of total area. The atoll, which surrounds a lagoon that extends over an area of more than 2,500 square kilometers, is an important nesting site for many species of birds.
11. Cayo Bolivar, Colombia
Cayo Bolivar, located 25 kilometers from San Andrés, Colombia coral island in the Caribbean Sea, is an uninhabited atoll consisting of two islands - East Cay and Western Cay. Its diversity of marine fauna and beautiful beaches made it popular place for tourist excursions.
10. Aldabra, Seychelles
Aldabra, uninhabited and extremely isolated, is a large atoll virtually untouched by man. Known as one of the "crown jewels" of the Indian Ocean, it has a distinctive island fauna, including the largest population of giant tortoises in the world.
9. Ari Atoll, Maldives
Ari Atoll is a natural atoll located in the Maldives. This is one of the largest atolls in the world and is located in the western part of the archipelago. There are more than 20 islands scattered here, most of which have been developed for tourist resorts, and each of them is autonomous and has places for living and recreation.
8. Bangaram Atoll, India
Bangaram Atoll, located in the Union Territory of Lakshadweep, India, is a popular tourist destination offering numerous recreational activities including scuba diving and snorkeling and deep sea fishing. It has white sandy beaches, a calm lagoon and stunning coral reefs.
7. Chagos Islands British Territory in the Indian Ocean
The Chagos Islands are a group of seven, consisting of more than 60 separate tropical islands in the Indian Ocean. Remarkable for their stunning biodiversity, these reefs are home to at least 371 species of coral, 784 species of fish and 2 species of turtles.
6. Pearl and Hermes Atoll, Hawaii
Pearl and Hermes Atoll, part of the Northwestern Islands of the Hawaiian archipelago, is a small Hawaiian atoll named after two British whaling ships that were wrecked on the atoll in 1822. The atoll was once a center for the pearl trade and is now a bird sanctuary.
5. Osprey Reef, Coral Sea Islands Territory
Osprey Reef, part of the northwestern group of islands in the Coral Sea, is an oval-shaped submerged atoll. The waters surrounding this atoll are 2 kilometers deep and the slopes of its reef are home to a diverse range of marine fauna, including the rare dwarf Nautilus pompilius.
4. Diego Garcia Atoll, British Indian Ocean Territory
Diego Garcia Atoll, located in the central Indian Ocean, just 7 degrees south of the equator, was settled by the French in the 1790s and was later ceded to the British Crown. It has the largest continuous rim of land of any atoll in the world.
3. Kwajalein Atoll, Marshall Islands
Kwajalein, part of the Republic of the Marshall Islands, is one of the largest atolls in the world, judging by the area of water it borders. It consists of 97 islands and islets, and its land area is 16 square kilometers. It surrounds a giant lagoon with an area of 2,174 square kilometers.
2. Kure Atoll, Hawaii
Kure Atoll, politically part of Hawaii, is the northernmost atoll in the world. This atoll is sometimes also called Ocean island. It provides habitat for hundreds of thousands of seabirds and numerous marine animals, including the monk seal.
1. Ducie Island, Pitcairn Islands
Ducie Island, located in the South Pacific Ocean, is a small uninhabited atoll in the Pitcairn Islands. Despite its sparse vegetation, the atoll is habitat for a number of bird species. More than 90 percent of the world's Typhoon Murphy population nests on Ducie.
In our minds, picturesque atolls with their turquoise lagoons and colorful reefs are closely associated with sea adventures and intense beach holiday.
For many, these strange formations are the embodiment of the dream of living on paradise island, overgrown with tall palm trees and tropical flowers. But what are atolls? geographical point vision? Where are they located and how do they appear on the surface of the oceans?
What does the word "atoll" mean?
Term "atoll" is of Maldivian origin. In the local tribal language the word Dhivehi atholhu means the administrative unit constituting the Maldives archipelago. IN English language the concept first appeared in 1625 thanks to Charles Darwin, who was closely involved in studying the structure of atolls and their distribution around the world.
Initially, the term was synonymous with a lagoon island, and later came to mean “an annular band of reef containing a lagoon.”
What is an atoll?
Today, an atoll is understood as a coral island in the form of a solid or broken ring surrounding a small body of water (lagoon). Most often, such islands are located either as an underwater mountain, which was partially washed away and submerged under water. The lagoon in this case is a volcanic crater, and the land is its rim, rising above the water. 
The height of the atoll, as a rule, does not exceed 3–4 meters above sea level. If the island ring is solid, then the water in the lagoon is less salty than in the ocean. If the ring is broken, then straits appear between individual sections of the island, thanks to which salty ocean water enters the lagoon.
What does the atoll consist of?
Structurally, the atoll includes three separate parts - the outer slopes of the island, the islet itself and the lagoon. The rim of the volcano is crowned with a superstructure formed by coral polyps.
In the process of their life activity, these invertebrate creatures form large colonies, which, as they develop and increase in size, create coral reefs. The rate of rifting in atolls is sufficient to compensate for the height of the islands, which gradually decreases with erosion and subsidence mountain peak.
How are atolls formed?
According to the theory of Charles Darwin, once on the site of atolls there were volcanoes and mountains, which as a result of eruptive and other geological processes sank under water. 
In the case of volcanoes, subsidence could be caused by eruptions, as a result of which the upper part of the peak collapsed under its own weight and formed a caldera. Over time, the volcanic edges were overgrown with coral reefs, forming a ring belt.
If the volcano does not completely sink under water, then a so-called nuclear atoll is formed, in the lagoon of which an island of volcanic origin remains. Due to the decline in sea level, some ring-shaped islands rise above the water and form raised atolls, which are an ordinary island (without a lagoon) with high marginal ridges along the perimeter. This is a fairly rare occurrence, but similar atoll formations can be found in the Tonga archipelago and in southern Micronesia.
Where are atolls formed?
Reef-building corals can only exist in warm waters oceans and seas, therefore atolls are formed exclusively in tropical and subtropical latitudes. The northernmost in the world is Kure Atoll, located in the northwestern part of the Hawaiian archipelago. To the south are the Elizabeth and Middleton atoll reefs, extending into the waters of the Coral Sea.
Most of the ring-shaped islands are concentrated in the Pacific and Indian Oceans– in the Maldives, Marshall and Caroline Islands, Seychelles, Chagos Archipelago and east of Australia. There are several small atoll groups in the Atlantic located east of Nicaragua. 
Kwajalein Atoll is recognized as one of the largest atolls in the world. Marshall Islands, consisting of 92 rings. His total area– more than 2300 km², of which over 90% are lagoons.
There are a huge number of islands in the world, some of them appeared tectonically, that is, due to movements of the earth's crust. Others broke away from continents. Finally, there are those for whose origin living organisms are responsible. The article will tell you what atolls are, how they appeared, and what their features are.
Etymology
The noun "atoll" comes from the Maldivian word "atolhu", which in turn comes from the root atollon, which in the native language means "closed, closed". This information alone is enough to suggest that the word “atoll” means something closed.
Meaning
By consulting any dictionary, you can find out the meaning of a term. What is an atoll? This is an island created by corals, in the shape of a ring (usually closed, although an interrupted version is also acceptable), located in the lagoon. It should also be noted that this is a certain elevation in the ocean, on which, thanks to coral organisms, a kind of land arose. Since such an elevation is located on the ocean floor most often on the crater of a dormant volcano, its corresponding shape is cone-shaped.
Considering what an atoll is, we note that it refers to biogenic islands, that is, created by living organisms.
Structure
The structure of such an island is of particular interest. It has 3 parts:
- Outer slope of the reef. Most of the time he's pretty cool. It is here that two opposing processes occur - the formation of coral material and its destruction under the influence of waves.
- Platform. It is a platform whose width can reach several hundred meters and even kilometers.
- Lagoon (water area inside the atoll). As a rule, it has a shallow depth and a flat bottom.
The average height of the atoll is usually 3-4 meters, the sizes can be very different. Thus, Kwajalein, the largest of the atolls, exceeds 2,300 km, more than 90% of which is in the lagoon, which stretches for 300 km.
In the following video you can see the amazing beauty of the atoll and learn some interesting facts about it.
Briefly about education
When considering what an atoll is, it is important to note special attention on how the formation of this island took place. Most often the process looked like this: around the crater extinct volcano a coral reef gradually appeared, forming a ring. When the water level dropped slightly, such an “island” appeared on the surface. This is how the atoll turned out. There are a lot of similar formations in the Pacific and Indian oceans, in tropical and subtropical latitudes.
The reverse process is also possible - immersion of the atoll in water. In this case, a so-called bank, or submerged atoll, is formed.
The main material from which such unusual islands are created is limestone, accumulated from the skeletons of dead plants and animals, primarily corals. The surface of such islands, as a rule, is decorated with rather poor vegetation cover, including several species of trees and grasses, located zonally. The most common species are Scaevolla fruticosa, Roofing pandanus, Ochrosia and others. Closer to the center, away from the shore, you can find ficus, hibiscus, as well as artificially planted breadfruit trees and coconut trees.
Other atolls are swampy, and plants other than sedge cannot survive on them.
So, considering the meaning of the word “atoll”, it should be noted that this is an oceanic island created from limestone - the remains of dead living organisms, primarily corals, having a lagoon and covered with some types of vegetation. Because of their picturesque and unusual nature, such islands are very attractive to tourists.
Let's continue our acquaintance with the atolls. We have already looked at what this word means, but now it is necessary to distinguish the term from a group of similar ones, first of all it is volcanic island and coral reef.
So, an island of volcanic origin is a piece of land located on the crater of an extinct volcano; it has nothing to do with the life of corals and other organisms. A coral reef is a deposit of dead coral found underwater on a volcanic crater.
If the water level decreases and sediments partially appear on the surface, an atoll is obtained.
The sequence can be represented like this:
- Corals settled on the crater of an extinct volcano, and gradually a kind of underwater organic skeleton was formed from their remains. This is a coral reef.
- When it was partially above the water column, it became an atoll.
Therefore, these terms are not synonymous, although they are close in meaning. We can say that an atoll is a certain type of coral reef, which has a round shape with a lagoon located in the central part, on which several tiny islands can be located.
In the photo you can see that the ocean waters surrounding the atolls have a striking turquoise color. It is connected with the fact that the interior of the island is gradually dying and decomposing.
We looked at what an atoll is, how it differs from similar terms and what it consists of.
