Geographic Encyclopedia. The formation of coral reefs according to Darwin's theory. Ari and Rasdhoo atolls
Every person has heard the word "atoll" at least once in their life. It came to us from Do you want to get to know this concept better and find out what an atoll is? Then let's start with a brief description.
Describing the concept
An atoll is called which looks like a complete or broken ring. Inside it is a lagoon, that is, a shallower body of water, which is separated from the sea or ocean waters narrow strip of coast. More exact description of what an atoll is - an elevation rising from the bottom of the ocean, on which a coral superstructure has formed. In shallow water, corals form reefs and groups of islands, between which there are straits. At their expense, the lagoons communicate with the ocean. But if the atoll is formed as a closed ring, then the waters in the lagoon have less salinity than in the surrounding ocean. They usually form on extinct volcanoes. The meaning of the word "atoll" can be found in any dictionary.
The structure and stages of the formation of atolls
For the first time Charles Darwin tried to explain the stages of formation of atolls. In the future, his assumptions were confirmed by numerous observations of modern scientists.
At the first stage, a volcano begins to act on the ocean floor. Volcanic islands rise slightly above the surface of the ocean. The slopes are gradually overgrown and the volcano itself is slowly sinking. Before a colony of polyps reaches the surface, a long period of time passes. Most of today's atolls formed after ice age. In order for such a formation to take the form of a closed ring, the sinking of the volcano and the growth of corals must proceed at approximately the same speed, otherwise the ring will be broken.
However, volcanoes may not sink 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;
- internal body of water, that is, the lagoon.
The average height rarely exceeds 4 meters above sea level, but the area of \u200b\u200bsuch formations can be quite large. So, the largest atoll on the planet is Kwajalein, which is included in the Marshall Islands archipelago. Its area is more than 2300 km². But 92% of this area falls on the lagoon. And about 15 km² remains on the island land.
Reef building material
Do you already understand what an atoll is? And what does the building material from which reefs are built look like? belong to the class of invertebrate benthic organisms. Those types of polyps that have a calcareous skeleton participate in reef formation. Most often, reefs consist of stony corals and several types of algae that are able to release lime from the surrounding water. Place of formation of coral reefs - shallow waters of tropical seas. Most of them are located in the Indian and pacific ocean.
Where does fresh water come from? How does vegetation appear?
Knowing what an atoll is, many are surprised at where fresh water and vegetation come from on coral islands. Rivers, streams and other sources of drinking water fresh water actually does not happen on the atolls. comes here only in the form of rain.
Waves, like giant millstones, grind some of the hardened corals and apply a layer of sand to the surface of the atolls. Seeds of various unpretentious plants get into this mixture. Most often, coconuts brought by the ocean sprout. Gradually limestone rocks are covered with palm trees and shrubs. Usually there are no animals on the atolls, but there is a huge variety of insects. And in the surrounding waters there are many species of fish.
atolls- coral islands in the form of solid or discontinuous rings surrounding the lagoon. In essence, an atoll is an elevation at the bottom of the ocean, which, as it were, is crowned with a coral superstructure. She, in turn, forms a reef with a group of small islands "motu", which are separated from each other by straits. The 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 the ocean. Elevation at the bottom of the ocean usually has a cone shape, formed on the site of an extinct volcano.
Major atolls of the Maldives
North Male Atoll
The city of Male is the capital of the Maldives, located on the main atoll - North Male. It is 69 km long and 39 km wide. This atoll includes 50 enough major islands and a few smaller ones. For tourists, North Male Atoll is attractive for its white sandy 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 It is 36 km long and 19 km wide. The resorts are usually reached by speed boats, and between the nearby islands, movement is carried out using motor boats.
Baa Atoll
Baa Atoll has 10 inhabited and 41 desert island. The atoll is 42 km long and 32 km wide. Basic concept local resort- Modern comfort combined with 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 to the east of Male and includes the large Ari and the small Rasdhoo atolls. Ari has approximately 70 islands. 18 of them are inhabited by people, and 26 are purely tourist area. 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 resort area is very popular. locals they make sails, collect and process corals, hunt sharks and turtles, from which a special oil is extracted to lubricate local boats.
Dhaalu Atoll
The main island of Dhaalu Atoll is Velavaru. It takes about 40 minutes to reach it by seaplane. The locals used to call it "turtle island". Here reigns lush tropical vegetation, tall palm trees, sandy beaches and an attractive picturesque lagoon. All this attracts turtles to the island (“velaa” - translated from local language dvivehi - "turtle") lovers of wildlife.
Laviani Atoll
This atoll is located far north of North Male at a distance of about 120 km from the latter. The Laviani Atoll consists of 63 islands, most of which are concentrated around barrier reef over 30 km. This is one of the best places for diving throughout the Maldives archipelago. Here incredible amount beautiful corals and colorful tropical fish. IN clear waters Laviani Atoll is home to some of the most beautiful creatures in the ocean, including glassfish, moray eels or large nurse sharks.
Addu Atoll
Addu Atoll is located 480 km from the capital Maldives, the cities of Male and international airport Hulule. This is the southernmost of the elements of the Maldives archipelago, located south of the equator. The island has a well-developed network of communications and roads. The largest island in the atoll is Gan, which is very different from the rest. It is 5 km long and 3 km wide. The island is covered with banana plantations and dense flowering vegetation. Gan is connected by dams to four neighboring islands, only slightly inferior to it in size. You can ride a bike along them, and the entire route will take only 20 km. The most beautiful lake here from October to March it receives a lot of wintering birds, and there are also places on the islands where you can swim.
In our minds, picturesque atolls with their turquoise lagoons and colorful reefs are closely associated with sea adventures and a rich beach holiday.
For many, these strange formations are the embodiment of a dream of living on paradise island, overgrown with tall palm trees and tropical flowers. But what are atolls? geographic 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 language of the local tribes, dhivehi, the word atholhu means the administrative unit constituting the Maldives archipelago. IN English language the concept first hit in 1625 thanks to Charles Darwin, who was closely involved in the study of the structure of atolls and their distribution around the world.
Initially, the term was synonymous with a lagoon island, and later came to mean "a ring-shaped reef ribbon 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 eroded 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 between the individual parts of the island there are straits, due to which salty ocean water enters the lagoon.
What is an atoll made of?
Structurally, the atoll includes three separate parts - the outer slopes of the island, the island itself and the lagoon. The rim of the volcano is crowned with a superstructure formed by coral polyps.
In the course of their life, these invertebrate creatures form large colonies, which, as they develop and increase, create coral reefs. The rate of rifting in the atolls is sufficient to make up for the height of the islets, which gradually decreases as the mountain top erodes and subsides.
How are atolls formed?
According to the theory of Charles Darwin, volcanoes and mountains once existed on the site of the atolls, which, as a result of eruptive and other geological processes, sank under water. 
In the case of volcanoes, subsidence could cause eruptions that caused the top of the summit to collapse under its own weight and form a caldera. Over time, the volcanic edges were overgrown with coral reefs that formed an annular 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 remains volcanic origin. Due to the decrease 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 ramparts around the perimeter. This is a rather rare occurrence, but similar atoll formations can be found in the Tonga archipelago and in southern Micronesia.
Where do atolls form?
Reef-building corals can only exist in warm waters 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 Hawaiian archipelago. South of all are the atoll reefs of Elizabeth and Middleton, stretching in the waters of the Coral Sea.
Majority ring-shaped islands concentrated in the Pacific and Indian Oceans - in the Maldives, the Marshall and Caroline Islands, the Seychelles, in the Chagos Archipelago and east of Australia. In the Atlantic there are several small atoll groups located east of Nicaragua. 
Kwajalein Atoll is one of the largest in the world. Marshall Islands, consisting of 92 rings. His total area- more than 2300 km², of which over 90% are lagoons.
Maldives - unique creation nature and amazing tourist facility. Located in the Indian Ocean near India, the state is a Muslim republic. At the same time, respect for tourists is so strong that due attention is paid to the main Christian holidays. The Republic of Maldives consists of several atolls, which, in turn, include numerous islands. Only 10 groups of atolls out of 20 are open for tourists to visit. At the same time, almost every hotel in the Maldives occupies a separate island, which gives tourists a sense of peace and serenity. However, for fans active rest there is something to do - there are plenty of opportunities for this on the islands, including diving, for which it is Island state visited by divers from all over the world. For all the exoticism, holidays in the Maldives are distinguished by the highest level of service.
In the material on Tourister.ru we will talk about structure Republic of Maldives- atolls and islands with their description and detailed information. Also you can explore detailed maps of atolls : , , And .
Kaafu Atoll (North Male)
Kaafu Atoll (South Male)
The atoll is divided from North Male Vadu Strait and stretches from west to east for 19 km and from north to south for 36 km. Only three islands of the pearl chain are occupied by local natives, the remaining 19 paradise turned into resorts and delight travelers from all over the world with gentle lagoons and marvelous beaches.
South Male is possible.
Vaavu Atoll
Alternative title: Felidhu
Located 65 km from the capital of the Maldives - Male (90 minutes by speedboat or 5 hours by regular boat). The atoll is an interesting geographical phenomenon, as it consists of two atolls: the main Vavu and a round one, 9 kilometers in diameter, located next to the main atoll. Five inhabited islands with a population of about 2,300 people, make Vaavu Atoll the smallest administratively in the Maldives. In addition to these five, there are about 14 other islands, but most of them are almost undeveloped by tourists compared to the islands of other atolls. Vaavu Atoll is considered one of the best diving spots in the Maldives.
The Fotteyo Kandu dive site is considered the best in the country and one of the top five in the world. Vaavu Atoll was opened to tourists in 1975, and has become a favorite with many organizers of various cruises and safaris in the Maldives. The reefs of the eastern side of the atoll are in an untouched state and are perfect for lovers of not only diving, but also snorkeling. There are a lot of sharks here, there is a chance to see hammerhead fish and other equally interesting fish.
Look detailed map atoll and read about tourist islands Wow you can.
Meemu Atoll
Alternative title: Mulaku
The atoll stretches for 50 kilometers from north to south and 30 kilometers wide, containing eight fishing islands and two resorts. There are excellent places for recreation and diving, which is confirmed by numerous cruises.
View a detailed map of the atoll and read about tourist islands Meem can.
Seenu Atoll
Alternative title: Addu
Most southern atoll, located right at the equator, stretching for 15 km from north to south and 18 km from west to east. It consists of 5 islands: northern Midu and western Hitado, Gan, Feidu and Marado, united by bridges. On the island of Gan, an airport and resort hotel, and large Khitadhoo ranks 2nd in terms of population after Male - 12,000 inhabitants. Green and pretty, Feidou and Marado rustle with plantations of coconut palms, nature has endowed them with small bays where fishing villages have settled down. A pleasant surprise awaits the guests of the hotel in Ghana - at any time they can visit the nearby islands and get acquainted with the life of local aborigines.
View a detailed map of the atoll and read about tourist islands Seenu can.
Faafu Atoll
Alternative title: Northern Nilande (Nilandhe Atholhu Uthuruburi)
A small atoll, has an oval shape and the second name is North Nilande. It stretches for 21 km from west to east and 45 km from north to south, containing five fishing islands and only one resort, relatively recently opened to travelers.
View a detailed map of the atoll and read about tourist islands Faafu can.
Dhaalu Atoll
Alternative title: Nilande South (Nilandhe Atholhu Dhekunuburi)
Dhaalu Atoll is located 150 km north of Male and 5 km from Faafu Atoll. It is also known as Nilandhe Atholhu Dhekunuburi (South Nilade Atoll). It is separated from North Nilade (Faafu Atoll) by the Strait of Deburieiterei Kandu. The airport and other atolls can be reached by seaplane or speedboat.
Dhaalu Atoll, 38 km long and 23 km wide, has about 46 islands, many of which are uninhabited. Seaplane transfer takes 40 minutes. For tourism, Dhaalu Atoll was opened quite recently. The islands open to tourists are located in the northern part of the atoll and provide excellent diving opportunities. The main island is Kudahuwadhoo. This is a fairly large island. developed infrastructure and a population of 1500 people.
The main reefs, interesting and accessible for diving, are located along the northern and northeastern parts of the islands. There are practically no shallow reefs inside the atoll.
Relatively clean from coral thickets, the lagoon allows you to safely go on a tour of the islands on a boat. Dhaalu Atoll still keeps the ruins of ancient monasteries and mosques. On the islands where he lives indigenous people Souvenirs are much cheaper than in the capital.
View a detailed map of the atoll and read about tourist islands Dhaalu is possible.
Alif Atoll
Alternative title: Ari (Ari), also the northern and southern parts are called Alif Alif and Alif Dhaal
The atoll stretches for 33 km from west to east and 96 km from north to south. The atoll is divided into two honors: Alif Alif (northern) and Alif Daal (south). In the northern part, in addition to the main atoll, there is a small Radsu atoll, and in the southern part, the capital Mahibadhoo. The atoll includes 70 islands, but only 18 of them are inhabited, and 25 have been turned into resorts. Once upon a time, local natives hunted sharks and turtles, but since sea hunting is banned, they have been busy servicing tourist hotels.
Baa Atoll
Alternative title: Malosmadulu (Maalhosmadulu Dhekunuburi)
It is an administrative unit of the Republic of Maldives, together with Horseborough Atoll, with the capital Eidafushi. The atoll stretches for 32 km from west to east and 42 km from north to south and includes 10 inhabited islands. Local aboriginals trade fishing, at the same time mastering more profitable tourism professions. Undersea world amazingly varied and surprising interesting places for diving. Marvelous corals, as yet untouched by divers, as well as dozens of fish species await ocean treasure hunters!
Lhaviyani Atoll
Alternative title: Miladunmadulu Uthuruburi
The atoll is 120 km away from the Maldivian capital, and therefore travelers arrive to rest by seaplane. The atoll stretches for 35 km from north to south and 37 km from west to east. Products and goods are brought here on dhoni, sailing such a considerable distance for 8 hours. Fadiffoulou contains 6 fishing and 4 resort islands.
View a detailed map of the atoll and read about tourist islands Lhaviyani is possible.
An atoll is a coral island that looks like a full or partial ring. In other words, the atolls are made up of turquoise lagoons, colorful reefs that blend seamlessly with marine life and are reminiscent of the wild and colorful life of the hero of Daniel Defoe's novel, Robinson Crusoe.
I suggest you admire the most beautiful atolls of the world from different corners our planet. See picturesque photos, find out Interesting Facts and share your impressions in the comments to this article.
1. Funafuti.
Tuvalu is an island nation located in the Pacific Ocean between Hawaii and Australia. It is the second least populated sovereign state in the world (the Vatican City legitimately took the primacy, with a smaller number of inhabitants). Due to the remoteness of the country, very few tourists visit it. 
2. Bikini Atoll.
This atoll is famous for two very interesting historical facts: Firstly, the famous bikini model bathing suit was named after the Bikini Atoll; secondly, this place was the field for 20 nuclear weapons tests: between 1946 and 1958. The indigenous people of these places were resettled even before the start of the tests. Today, the islands are completely safe to visit. Many tourists come here to dive underwater and visit sunken ships. 
3. Tubbataha reef.
Tubbataha Reef is one of the best diving spots in the world. Located in the Philippines, the reef consists of two atolls: North and South, which are separated by an 8-kilometer wide channel. Coral reefs- Not only perfect place for diving, it is also an excellent habitat for many colonies of exotic fish. 
4. Big blue hole.
Lighthouse Reef is probably the most popular of the atolls in the world, and this is due to the large blue hole, which is located in the very center of the atoll. This is a real unexplored paradise for divers who flock here from all over the world. The deeper one goes into blue hole, the clearer the water and the more breathtaking scenery. 
5. Tikehau.
Tikehau is part of the Tuamotu chain of atolls, covering an area in the Pacific Ocean that is the same size as Western Europe. This place attracts tourists with its white - pink sand islands, inside which turquoise lagoons serve as shelters for all kinds of exotic fish. The research team of Jacques Cousteau, who visited these places, came to the conclusion that this place has the largest concentration of fish in French Polynesia. 
6. Caroline Island
Europeans first saw the island in 1606. Carelyn is now part of the Republic of Kiribati. Despite more than 300 years of human activity on this island, it is one of the world's most pristine tropical islands and the world's most pristine atoll. Caroline Island and its neighbor Flint Island are home to the world's largest crab populations. The islands are located at an altitude of 6 meters above sea level, which means that they are in danger of disappearing due to the constantly rising sea level. According to scientists' calculations, the islands could be completely submerged by 2025. 
7. Aitutaki Atoll.
Aitutaki consists of several coral and volcanic islands that have a triangular lagoon. Classical palm island turquoise shallow water, corals, exotic fish - all this you will find when you get to Aitutaki. The most popular is the island of Tapuaetai - a small island in the southeast of the lagoon. 
8. Aldabra.
Aldabra is one of Outer Islands Seychelles, more than 1,100 kilometers (700 miles) from Mahe, the big island on Seychelles. It is the second largest atoll in the world after Kiritimati. Due to the difficulty of accessing Aldabra Atoll, it is virtually untouched by man. About 152,000 giant tortoises live on its territory. 
9. Rangiroa.
Rangiroa is one of the largest atolls in the world and the largest atoll in the Tuamotu archipelago. This place is ideal for diving, because of the deep lagoon, full of abundance marine life. You can also see sharks here sea turtles and dolphins. 
10. Atolls of the Maldives.
Tiny country in the Maldives, in the middle indian ocean consists of about 1200 tiny coral islands grouped into 26 atolls. The main occupation for tourists here is the study of alluring depths, which is accessible due to excellent visibility. Depth exploration includes the exploration of wrecks, which can be found with the help of guides. 
