What are atolls? Structure and stages of education. Ari and Rasdhoo atolls

Atolls- coral islands in the form of continuous or discontinuous rings surrounding the lagoon. Essentially, an atoll is an elevation on the ocean floor, which is, as it were, crowned with a coral superstructure. It, in turn, forms a reef with a group of small “motu” islands, which are separated from each other by straits. Straits connect the inner lagoon to the surrounding ocean. If there are no such straits, then the land forms a continuous ring. In this case, the water in the lagoon is often less salty than ocean water. The rise on the ocean floor is usually cone-shaped, formed on the site of an extinct volcano.

Main atolls of the Maldives

North Male Atoll

The city of Male is the capital of the Maldives, located on the main atoll - North Male. Its length is 69 km and its width is 39 km. This atoll includes 50 fairly large islands and several small ones. For tourists, North Male Atoll is attractive for its snow-white beaches, turquoise lagoons and cozy atmosphere.

South Male Atoll

This atoll consists of three dozen islands, and only three of them are inhabited. 10 islands are uninhabited, and 17 are hotels. South Male is 36 km long and 19 km wide. Resorts are usually reached by speedboats, and travel between nearby islands is carried out using motor boats.

Baa Atoll

Baa Atoll consists of 10 inhabited and 41 uninhabited islands. The length of the atoll is 42 km, width is 32 km. The main concept of the local resort is a modern level of comfort combined with the Robinson Crusoe lifestyle.

Ari and Rasdhoo atolls

Ari Atoll is 33 km long and 96 km wide (from north to south). The atoll is located east of Male and includes the large Ari and small Rasdhu atolls. Ari has approximately 70 islands. 18 of them are inhabited by people, and 26 are purely tourist areas. These are fairly new resorts, the construction of which took place in the 90s. Now the influx of tourists to Ari has reached its peak and the resort area is very popular. Local residents make sails, collect and process corals, hunt sharks and turtles, from which they extract special oil for lubricating local boats.

Dhaalu Atoll

The main island of Dhaalu Atoll is Velavaru. It takes about 40 minutes to reach it by seaplane. Locals used to call it “turtle island.” It is home to lush tropical vegetation, tall palm trees, sandy beaches and an attractive picturesque lagoon. All this attracts turtles (“velaa” - translated from the local language Dwivehi - “turtle”) to the island of wildlife lovers.

Lhaviani Atoll

This atoll is located far north of North Male at a distance of about 120 km from the latter. Lhaviani Atoll consists of 63 islands, the main part of which is concentrated around a barrier reef for 30 km. This is one of the best diving spots in the entire Maldives archipelago. There is an incredible amount of beautiful corals and colorful tropical fish. In the clear waters of Lhaviani Atoll you can find the most beautiful inhabitants of the ocean, including glass fish, moray eels or large nurse sharks.

Addu Atoll

Addu Atoll is located 480 km from the capital of the Maldives, the city of Male and Hulhule International Airport. It is the southernmost element of the Maldives archipelago, located south of the equator. The island has a well-developed communications network and roads. The largest island in the atoll is Gan, which is very different from the others. Its length is 5 km and width is 3 km. The island is covered with banana plantations and dense flowering vegetation. Gan is connected by causeways to four neighboring islands, only slightly smaller in size. You can ride a bicycle along them, and the entire route will take only 20 km. The beautiful lake here welcomes many wintering birds from October to March, and there are also places on the islands where you can swim.

Separated by straits. These straits connect the ocean to the lagoon. If there are no straits, then the land forms a continuous ring, in which case the water in the lagoon may be less salty than in the ocean. A rise on the ocean floor is usually shaped like a cone, formed by an extinct volcano.

A typical atoll consists of three parts: the outer reef slope, the reef platform and the lagoon. The height of the atoll usually does not exceed 3-4 meters above mean ocean level. Atolls can have a variety of configurations and sizes. One of the largest atolls on Earth - Kwajelein (Menshikova) in the Marshall Islands archipelago - reaches 2336 km², of which 92% is a lagoon stretching for 300 km. The total area of ​​the 92 islands of this atoll is 14.5 km². Another large atoll, Rangiroa (Rangiroi) in the Tuamotu archipelago, covers 1639 km², and its 241 islets occupy 43 km². The coral reefs of such large atolls frame a rise on the ocean floor, which is a volcanic plateau, and not the cone of a separate volcano. With the exception of small atolls, the area of ​​reefs usually accounts for a few percent of the area of ​​the atolls themselves, while the land area often accounts for only a fraction of a percent. In the case of the small Pangelaya Atoll, reefs and land account for 3 of the 4 km² of the atoll area.

Atolls are usually formed by overgrowing a volcanic island with a coral reef, forming a ring belt. This is often accompanied by the immersion of the volcanic base under water; if such immersion does not occur, then a nuclear atoll is formed with a volcanic island inside the lagoon. A slight decrease in water level (or a rise in the tectonic basis of the atoll) leads to the transformation of a coral reef into an atoll. Further uplift of land may result in the formation of an uplifted atoll. If the atoll is submerged under water, then an underwater bank (that is, a sandbank) is formed, which can be called a submerged atoll.

Illustrations

Literature

  • Ignatiev G.M. Tropical Islands of the Pacific Ocean. Moscow, Mysl Publishing House, 1978, 270 p.
  • Scott G. A. J., Rotondo G. M. "A model for the development of types of atolls and volcanic islands on the Pacific lithospheric plate". USA, Washington D.C.: Smithsonian Institution, 1983.
  • Rapaport Moshe. “Population pressure on cowl atolls: trends and approaching limits.” USA, Washington D.C.: Smithsonian Institution, 1990.

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See what “Coral Atoll” is in other dictionaries:

    Atoll Atoll is a coral island that looks like a continuous or discontinuous ring surrounding a lagoon. Atholl (Scotland) historical region in the center of Scotland, in the mountains north of Perthshire ... Wikipedia

    A ring-shaped coral reef surrounding the water area. Coral reefs are distributed in tropical and subtropical latitudes, most widely in the Pacific and Indian oceans. The word atoll comes from the name used among the peoples... ... Collier's Encyclopedia

    - (Atoll) lagoon reef, a special type of island. A ring-shaped strip of land surrounding an inland shallow lake or lagoon. Usually A. rises several meters above sea level. The depth in the lagoon is small; 60 150 m (30 80 nautical fathoms), whereas ... ... Marine Dictionary

    Coral island, reef Dictionary of Russian synonyms. atoll noun, number of synonyms: 9 bikini (5) ... Synonym dictionary

    atoll- a, m. atoll m., English. Coral island. Atoll aya, oh. Sometimes the tentacles of an octopus stuck into the hole, which apparently methodically searched the atoll bank. A. Kim Fish Simplicitas. // NM 1997 4 102. Lex. Dal: atol; Toll 1863: atoll; SAN 1891 ... Historical Dictionary of Gallicisms of the Russian Language

    ATOLL, a ring-shaped CORAL REEF surrounding a shallow LAGOON. A reef appears initially as the frame of an island slowly sinking into water, usually of volcanic origin. As the island sinks, the corals continue to grow... Scientific and technical encyclopedic dictionary

    ATOLL, atoll, husband. (Malay). Ring-shaped coral island. Ushakov's explanatory dictionary. D.N. Ushakov. 1935 1940 … Ushakov's Explanatory Dictionary

    ATOLL, ah, husband. Ring-shaped coral island. | adj. atoll, oh, oh. Ozhegov's explanatory dictionary. S.I. Ozhegov, N.Yu. Shvedova. 1949 1992 … Ozhegov's Explanatory Dictionary

    Husband. 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 (the lagoon can be converted into a Russian lagoon). Dahl's Explanatory Dictionary. IN AND. Dal... ... Dahl's Explanatory Dictionary

    - [Malay adol enclosed] a coral island in the form of a narrow circular ridge of reef limestone (coral barrier) enclosing an inner lagoon. The outer slope is steep (about 45-60°), sometimes even overhanging. On the inside of the ring it is often... ... Geological encyclopedia

Books

  • 50 most beautiful islands on the planet, Anthony Mason, Dream Island - what do we mean by this concept? The simplest answer is a coral atoll in the tropics, snow-white sand beaches with the shadow of a coconut palm, the leaves of which rustle quietly under... Category: General questions Publisher:

In our minds, picturesque atolls with their turquoise lagoons and colorful reefs are closely associated with sea adventures and eventful beach holidays.


For many, these strange formations are the embodiment of the dream of life on a paradise island covered with tall palm trees and tropical flowers. But what are atolls from a geographical point of view? 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. The concept first came into English 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 as the mountain peak subsides and erodes.

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-forming corals can only exist in the warm waters of oceans and seas, so 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, in the Chagos Archipelago and east of Australia. There are several small atoll groups in the Atlantic located east of Nicaragua.


Kwajalein Atoll in the Marshall Islands, consisting of 92 rings, is recognized as one of the largest in the world. Its total area is more than 2,300 km², of which over 90% is lagoons.

An atoll is a coral island that partially or completely surrounds a lagoon. Atolls can come in a wide variety of shapes, configurations and sizes. The atoll's corals crown high points on the ocean floor, be it the edge of a vanished seamount or a volcano, which have eroded or partially collapsed over time underwater. A lagoon forms above a volcanic crater or caldera, while the upper edge remains above water or at shallow depths, allowing corals to grow and form reefs. Since corals grow exclusively in warm seas, atolls are found only in the tropical and subtropical zones of the Earth. For many people, stunning atolls with vibrant coral reefs and pristine turquoise lagoons seem inseparable from incredible sea adventures and paradisiacal beach holidays.

10. Funafuti, Tuvalu

Tuvalu is a Pacific country in the western part of Polynesia, which consists of 4 islands and 5 atolls scattered over 350 kilometers. "Tuvalu" translated from the local language means "eight standing together" (that is the number of inhabited islands in Tuvalu). If you look at the map, the state is located midway between Australia and Hawaii, and is probably best known for its Internet domain ".tv". In terms of population, Tuvalu is the second smallest sovereign state in the world, with only the Vatican City having fewer inhabitants. Due to the remoteness of the country, very few tourists visit Tuvalu. The capital of Tuvalu, Funafuti, is a small coral atoll. Its width is about 20 meters at the narrowest part, and about 400 meters at the widest part of the island. The capital has approximately 4,500 inhabitants and is a key location. Near the airport there are administrative buildings, a beautiful church and one hotel.


An island is a piece of land that is separated from the mainland on all sides by water. On our planet you can count approximately half a million large and tiny...

9. Bikini Atoll, Marshall Islands

Bikini Atoll is famous for three things: firstly, in 1946, a women's revealing bikini swimsuit was named after this atoll; secondly, the events described by Janusz Wisniewski in the novel of the same name took place here; and thirdly, during the US Pacific nuclear tests, a total of 67 tests took place here over a 12-year period from 1946 to 1958. The island's 167 residents were relocated to nearby safe islands. Today, Bikini Atoll is safe to visit and its background radiation is now lower than most major cities, but the soil still contains dangerous levels of radioactive material. Fish are unaffected and are found in abundance here due to the lack of fishermen. Most visitors to the atoll are diving enthusiasts who dive into ships sunk during testing in 1946.

8. Tubbataha Reef, Philippines

Tubbataha Reef Natural Park covers an area of ​​130 hectares, including the northern and southern atolls. This is a unique example of an atoll reef with a very high density of marine species. The northern atoll serves as a nesting site for birds and sea turtles. The natural park is a wonderful example of a pristine coral reef with a spectacular 100-metre perpendicular wall, extensive lagoons and two coral islands. Tubbataha is in a unique position - in the heart of the Sulu Sea. The reef is home to whales, dolphins, sharks, turtles and napoleon fish. In total, the reef ecosystem supports more than 350 species of coral and about 500 species of fish. Tubbataha Reef is one of the best diving spots in the Philippine Islands and is listed as a UNESCO World Heritage Site.

7. Lighthouse Reef, Belize

Lighthouse Reef is the most distant from the coast of all the atolls in Belize. However, it is very small, about 80 kilometers long. However, it offers the best diving in the entire Caribbean. Lighthouse Reef is incredibly popular among other atolls due to the large 300 meter diameter blue hole that lies near its center. The Great Blue Hole offers divers interesting observations of the limestone formations (during the Ice Age, a system of limestone caves was formed here, flooded due to rising sea levels) that form its walls. Divers can encounter several interesting species of fish, including giant grouper, nurse sharks and several species of reef sharks, such as the Caribbean reef shark.

6. Tikehau or Krusenstern Atoll, French Polynesia

Tikehau is located at the northwestern tip of the Tuamotu archipelago. It was discovered by the Russian navigator Otto Kotzebue in 1816. This atoll is almost circular in shape with a maximum diameter of 28 kilometers and consists of two large islands and numerous small islets. Almost the entire territory of the atoll, except for the northeastern part, is inhabited, with 400 inhabitants (according to the 1996 census), most of whom live in the village of Tuherahera. Tikehau is undoubtedly a picture postcard with long stretches of white or pink sandy islands within which a turquoise lagoon harbors the most amazing variety of fish.

5. Caroline Island, Republic of Kiribati

First discovered by Europeans in 1606, then annexed by Britain, and finally becoming part of the independent Republic of Kiribati in 1979, Caroline Island is famous for being the first on Earth (outside Antarctica) to be invaded on January 1, 2000. The island is one of the most pristine tropical islands and one of the most pristine atolls in the world. It is home to one of the world's largest populations of palm thief (a type of crab) and an important nesting site for seabirds, most notably the black tern. However, due to the fact that the highest point of the island is located at a distance of 6 meters from sea level, there is a real threat of its flooding due to global warming and subsequent sea level rise. The Government of Kiribati estimates that this could happen as early as 2025.


The islands, which have not yet been penetrated by cars, now provide a unique opportunity to relax without these monsters, in a relaxed, relaxed...

4. Aitutaki Atoll, Cook Islands

Aitutaki Atoll consists of several volcanic and coral islets around a triangular lagoon. The entire lagoon and its islands are stunningly beautiful. A classic postcard featuring a palm tree fringed tropical island with shallow, warm turquoise waters, corals, tropical fish and blue skies. The most popular attraction is Tapuaetai (one-legged island), a small islet in the southeast of the lagoon. In 2006, the American television show Lost: Cook Islands was filmed on Aitutaki.

3. Aldabra, Seychelles

Located in the Indian Ocean, Aldabra Atoll is an outstanding example of an uplifted coral atoll. It is one of the largest atolls in the world (only Christmas Island in Kiribati is larger) and contains one of the most important natural habitats for the study of evolutionary and ecological processes. Aldabra Atoll consists of four large coral islands that surround a shallow lagoon; the group of islands is itself surrounded by a coral reef. Due to difficulties of access and isolation, Aldabra Atoll has been protected from human influence and thus preserved some 152,000 giant tortoises, the world's largest population of this reptile. Marine habitats range from coral reefs to seagrasses and mangroves. In 1982, Aldabra Atoll was included in the UNESCO World Heritage List as a unique natural monument. In 2015, Czech filmmakers shot and released the full-length documentary film “Aldabra. Journey to a mysterious island”, telling about the unique flora and fauna of the island.


There are a huge number of islands in the Mediterranean Sea, numbering in the thousands, and many of them have their own history and mysteries that have not yet been solved...


2. Rangiroa, French Polynesia

Rangiroa is one of the largest atolls in the world and the largest atoll in the Tuamotu archipelago. The land area of ​​79 km² is a cluster of 415 small islands. Rangiroa is a prime spot for snorkeling due to the lagoon's clear blue water and exceptional marine life diversity. Popular diving spots include the Blue Lagoon and Tiputa Pass. Here you can easily encounter gray reef sharks, rays, manta rays, dolphins, tuna and hammerhead fish.

1. Atolls of the Maldives

The Maldives is a group of islands in the Indian Ocean near India. The people of the Maldives are called Maldivians and their language is known as "Dhivehi". The Maldives consists of atolls, coral reefs and coral islands, slightly rising above sea level: the highest point of the archipelago is on the southern Addu (Sienu) atoll - 2.4 m. In total, the state was formed from 26 geographical atolls, which include about 1200 islands, which are divided into 20 administrative units. Not all the islands are inhabited, in fact only about 200 islands. The rest are used for various activities, the most important of which is tourism. The Maldives Reef is called one of the wonders of the world in terms of marine life and coral biodiversity. The word “atoll” itself originates from the Maldivian word “atholhu”.

Every person has heard the word “atoll” at least once in their life. It came to us from Do you want to take a closer look at this concept and find out what an atoll is? Then let's start with a brief description.

We describe the concept

An atoll is called an atoll that looks like a complete or broken ring. Inside it there is a lagoon, that is, a smaller body of water, which is separated from sea or ocean waters by a narrow strip of shore. A more accurate description of what an atoll is is a rise rising from the ocean floor on which a coral superstructure has formed. In shallow waters, corals form reefs and groups of islands, between which there are straits. Thanks to them, the lagoons communicate with the ocean. But if the atoll is formed as a closed ring, then the waters in the lagoon have lower salinity than in the surrounding ocean. They usually form on extinct volcanoes. The meaning of the word "atoll" can be found in any dictionary.

Structure and stages of atoll formation

Charles Darwin was the first to try to explain the stages of atoll formation. Subsequently, his assumptions were confirmed by numerous observations of modern scientists.

At the first stage, a volcano begins to operate on the ocean floor. Volcanic islands rise somewhat above the surface of the ocean. The slopes are gradually overgrown and the volcano itself is slowly sinking. It takes a long period of time before a colony of polyps reaches the surface. Most of today's atolls were formed after the Ice Age. In order for such a formation to take the form of a closed ring, the subsidence of the volcano and the growth of corals must proceed at approximately the same speed, otherwise the ring will be torn.

However, volcanoes may not submerge into the ocean, in which case a volcanic island remains inside the lagoon. This formation is called somewhat aggressively - a nuclear atoll. There can be many islands formed by coral colonies.

Each atoll has 3 components:

  • outer reef slope;
  • dense reef platform;
  • an internal body of water, that is, a lagoon.

The average height rarely exceeds 4 meters above sea level, but the area of ​​such formations can be quite large. Thus, the largest atoll on the planet is considered to be Kwajalein, which is included in the Marshall Islands archipelago. Its area is more than 2300 km². But 92% of this area is lagoon. And about 15 km² remains on the island land.

Reef building material

Have you already understood what an atoll is? What does the building material from which reefs are built look like? belong to the class of invertebrate bottom organisms. Those types of polyps that have a calcareous skeleton participate in reef formation. Most often, reefs consist of madrepore corals and several types of algae that are capable of releasing lime from the surrounding water. The place where coral reefs form is in the shallow waters of tropical seas. Most of them are located in the Indian and Pacific Oceans.

Where does fresh water come from? How does vegetation appear?

Knowing what an atoll is, many are surprised where fresh water and vegetation come from on the coral islands. There are virtually no rivers, streams or other sources of drinking fresh water on the atolls. It comes here only in the form of rain.

The waves, like giant millstones, grind some of the hardened corals and deposit a layer of sand on the surface of the atolls. This mixture contains seeds of various unpretentious plants. Most often, coconuts brought by the ocean germinate. Gradually, the limestone rocks are covered with palm trees and shrubs. There are usually no animals on atolls, but there is a huge variety of insects. And in the surrounding waters there are many species of fish.