What is the name of an island built by corals? See what "Coral Islands" are in other dictionaries

Coral Islands

Coral island- an island that arose as a result of the vital activity of reef-building organisms in the oceans and seas of the tropical zone. A coral island in the form of a continuous or broken ring is called an atoll.

Notes

• Ignatiev G.M. Tropical Islands of the Pacific Ocean. Moscow, Mysl Publishing House, 1978, 270 p.

Wikimedia Foundation.

• 2010.
• Coral snakes

Coral Atoll

See what "Coral Islands" are in other dictionaries: CORAL ISLANDS - islands that arose as a result of the vital activity of reef-building organisms in the oceans and seas of the tropical zone...

Big Encyclopedic Dictionary coral islands - islands that arose as a result of the vital activity of reef-building organisms in the oceans and seas of the tropical zone. * * * CORAL ISLANDS CORAL ISLANDS, islands that arose as a result of the vital activity of reef-building organisms in the oceans and... ...

encyclopedic Dictionary Coral Islands

See what "Coral Islands" are in other dictionaries:- islands formed on the surface of coral structures (See Coral structures), as a result of the activity of waves and surf from the products of mechanical destruction of coral limestones and colonies of living corals ... - islands that arose as a result of the vital activity of reef-building organisms in the oceans and seas of the tropics. belts...

Natural science. encyclopedic Dictionary Coral structures - coral reefs, geological formations formed as a result of the life activity of colonial coral polyps (mainly madrepore corals (See Madrepore corals)) and accompanying organisms capable of extracting ...

Great Soviet Encyclopedia islands - islands that arose as a result of the vital activity of reef-building organisms in the oceans and seas of the tropical zone. * * * CORAL ISLANDS CORAL ISLANDS, islands that arose as a result of the vital activity of reef-building organisms in the oceans and... ...

- areas of land surrounded on all sides by the waters of oceans, seas, lakes, and rivers. They differ from the continents in their relatively small size. There are single islands and their groups (archipelagos). Islands in the oceans and seas are divided into continental ones... ... Coral reefs - structures made of organic limestones located near sea level or at shallow depths in the coastal zone of tropical seas or in shallow waters warm seas . They are massive deposits of calcite (limestone),... ...

Geographical encyclopedia- (Anthozoa), class marine. cnidarians. Colonial, less often single polyps; jellyfish do not form. Many have a calcareous or horny skeleton. Dept. individuals are usually cylindrical. forms, with their base fused with the colony or (single, capable of slowly... ... Biological encyclopedic dictionary

Friendship Islands

Tonga Islands- Coordinates: 20°35′16″ S. w. 174°48′37″ W. long / 20.587778° S w. 174.810278° W d. ... Wikipedia

Books

• Underwater kingdom. Red Sea, Maldives, Malaysia, Caribbean Sea, Angelo Moggetta, Andrea Ferrari, Antonella Ferrari. Bizarre reefs and coral platforms, high rocks falling straight into the abyss of turquoise water, picturesque straits where life unknown to us is in full swing - we really want to dive into this underwater... Buy for 2300 rubles
• Underwater kingdom of the Red Sea Maldives, Mogetta A., Ferrari A.. Bizarre reefs and coral platforms, high rocks falling straight into the abyss of turquoise water, picturesque straits - you really want to dive into this underwater paradise, admire its unearthly...

On the coasts of tropical seas, an active role in the formation of seashores may belong to some marine organisms, and primarily to various reef builders - six- and eight-rayed corals, accompanying calcareous algae (Litotamnyon, Halimeda), various hydroids and bryozoans. These organisms are able to assimilate lime from seawater and build their skeletons from it, from which they

the death of corals and algae, their destruction by waves and surf, and

subsequent cementation of the destruction products forms a massive rock - coral, or reef, limestone.

Accumulative forms built from reef limestone are called coral reefs. There are several types of coral structures: fringing, or coastal, barrier, ring and intralagoonal reefs.

Fringing reefs are underwater coral-limestone terraces adjacent directly to the shore. Their outer zone is covered with living colonies of corals. The surface of the reef - the so-called reef flat - with distance from the outer zone is increasingly covered with a sediment cover of coral gravel and sand. Near the shore it is bordered by a snow-white sand and gravel beach.

On tectonically stable shores, the thickness of the fringing coral reef usually does not exceed 50 m. This is due to the living conditions of the reef-forming corals. Reef-building coral polyps live in symbiosis with the unicellular green alga Zooxantella, which lives in the polyp cavity and requires good light for photosynthesis. This most important ecological condition is no longer satisfied at depths greater than 50 m. Barrier reefs are coral-limestone ridges or

barriers located at a more or less significant distance from the shore. The thickness of the barrier reef is usually many times greater than the thickness of the fringing reefs. From the above-mentioned ecological features of the habitat of reef-forming corals, it follows that the greater thickness of the reef limestone composing the barrier reef can be achieved only under the condition of tectonic subsidence of the reef base. This is exactly how Charles Darwin, one of the first creators of the theory of the formation and development of coral reefs, explained this fact. Thus, barrier reefs

arise as a result of the subsidence of the coastal reef under the condition of constant growth of its outer edge in height. The world's largest structure of this kind is the Great Barrier Reef, which stretches along the northeastern edge of Australia for more than 2000 km. If a barrier reef forms around a small subducting island, it will transform into a ring-shaped reef, or atoll, as the base sinks and the outer edge continues to grow.

The water area located inside the atoll or fenced off from open sea barrier reef is called a coral lagoon. Special types of reef-forming corals settle in the lagoon, which, in the course of their life activity, create another type of reef structures - intralagoonal reefs. In most cases, they take the form of columns or giant pedestals, randomly scattered throughout the lagoon and usually called pinnacles (from English - spire, pointed turret). Pinnacles merging with each other form larger formations -

coral banks patches. Sometimes intralagoonal reefs form on the crests of underwater ridges built by tidal currents.

How in open ocean, and coral islands are scattered in abundance in the coastal zones of tropical seas. It is usually believed that coral islands are built by corals, that they are former coral reefs. However, this is not the case. Although islands are sometimes found in the oceans - raised coral reefs (Nauru Island in the Pacific Ocean, Tromelin Island in Indian Ocean etc.), but such formations are rare. Ordinary coral islands, including islands located on atolls, are typical island bars, built with the help of the action of sea waves from coral sediments - sand, gravel, pebbles, and sometimes heaps of blocks of reef limestone. The scheme of bar formation, which was discussed above, is generally applicable to explain their formation.

Biogenic islands are found only in the tropical and equatorial latitudinal zones of the ocean with warm waters. Based on the composition of the substrate, atolls, coral reefs and mangrove islands are distinguished. However, the latter are small in size and have a very limited distribution in the coastal zone. Coral formations are fringing reefs stretching along the coast, or barrier reefs located at a distance from the coast and separated from them by lagoons. Most of the reefs are underwater, and only their tops protrude above the ocean level in the form of small islands of intricate shapes, for example, on the Great Barrier Reef at eastern shore Australia. Atolls in the ocean arise on the tops of large underwater volcanic mountains or during the long-term evolution of a ring fringing reef around volcanic islands, subsequently sank below ocean level and covered by a layer of coral limestone. As a result, circular low islands are formed, composed of coral sand - a product of the destruction of reefs that surround the internal shallow lagoon, for example, the Caroline, Marshall, Gilbert, Line, Tuamotu islands - in the Pacific Ocean, the Malvinas and Chagos islands - in the Indian Ocean, the Albuquerque Islands, Saint-Andrés, Roncador - in Atlantic Ocean(Caribbean Sea) and others. These islands are young formations resulting from the superstructure of coral reefs during the Holocene.

From the name it is clear that such names were given to islands that “grew” from coral reefs. It looks like this. First, an active underwater volcano, having completed its last eruption, rises above the surface of the water and fades away. It is surrounded on all sides by coral reefs, whose roots reach ocean floor. Over time, the volcano settles or collapses, but the reefs remain in place, repeating its contours and continuing to grow. In the end, only a “plate” of the island remains above the surface with a shallow central lagoon, which shows the mouth of the former volcano.

The central lagoon of the island is the most a nice place island, which is deservedly its attraction.

This type of island is a favorite holiday destination for people from all over the world, being business card beautiful Pacific Islands(Figure 4)

Coral reefs grow not only by turning hard corals into sand, raising the level of the seabed. An equally important source of their formation is the sticky substance that is secreted by both polyps and individual algae that settle on them. This substance cements all calcareous remains into an indestructible rock surface.

Figure 4. - Coral islands. Maldives.

In the tropics it rains quite often. Then the concentration of salt in the surface layers of sea water decreases sharply, and many polyps die. Sometimes clouds of silt and sand float in, which, settling, bury animals underneath. Dead coral colonies crumble and turn into coral sand.

Thus, coral formations arise from endless processes of creation and destruction.

People have long been interested in how reefs form, especially atolls found right in the open ocean.

The famous Russian navigator F. F. Bellingshausen expressed a number of correct thoughts about their nature. The most substantiated theory of the origin of coral reefs was put forward by Charles Darwin. In many respects they still adhere to it today.

The formation of atolls does not always fit into the scheme put forward by Darwin. Some of them originate on the tops of underwater volcanoes or on sea shallows. This is evidenced, for example, by the results of drilling the coastal reef at Pago Pago on the Samoan Islands, where bedrock (not corals) is already at a depth of 35 m from the surface.

The English scientist J. Murray made significant additions to Darwin's theory. He proved that a continuous coral reef will necessarily transform into a ring one, and for this reason. The corals in the middle part of the reef do not have enough food, they gradually die and are destroyed, because carbon dioxide accumulates here - a product of the respiration of polyps, which dissolves the limestone, and the reef grows only from the outside. This is how a lagoon appears in the center of the reef.

V. N. Kosmynin, who studied in detail the geomorphology of coral reefs Seychelles, found on them a number of successive stages of formation of the relief of the outer slope. In the first stages, spurs are strips of dense interlacing of branched corals stretched from top to bottom of the slope. Such corals are characterized by rapid growth, and for a long time they keep up with relatively short term to form a so-called coral bush on the reefrock. Under the influence of waves, the delicate terminal branches of the colonies break off, and their bases, meanwhile, undergo cementation by calcareous algae and encrusting corals.

On this seemingly compressed and therefore denser vertical strip of coral limestone, as if on a pock, branched corals grow again - and the formation of the spur moves into the second stage.

The appearance of channels, i.e., recesses between the spurs, is partly explained by erosion under the influence of water flowing from the reef, which, when the wave recedes, rushes here, since it does not encounter obstacles in the form of coral thickets. However, the main reason for the appearance of channels is still the growth of corals on the spurs. At the last stage, the width of the spurs along the front reaches 3-5 m, and sometimes more, and they begin to close with their sides, and then the channels between them turn into vertical or inclined tunnels.

From the above it is obvious that the reef grows towards the sea due to the formation of spurs and their subsequent fusion. Of course, their erosional destruction is not excluded, but this, apparently, occurs only during very strong storms.

On the above-mentioned reef on Hainan Island, the system of spurs and channels was in the third, most developed stage.

The ridge crowning the outer slope of the reef rises somewhat above the zero depth level, behind it a more or less flat limestone platform, or rifflet, stretches towards the shore.

Directly behind the ridge on the rifflet there is almost always a depression ranging from 50 cm to 1-2 m in depth and several meters in width. It runs in a winding channel parallel to the outer edge of the reef. As mentioned above, the reef crest is the place of the most active growth of corals, and on it, due to calcareous algae, the so-called algal bank develops.

The formation of a rising ridge by calcareous red algae precisely at the seaward edge of the riffle and on the ridge is explained by the ecological characteristics of these plant organisms. They tolerate overheating and drying out much more easily than madrepore corals. The conditions of periodic exposure and splashing by waves for calcareous scarlet plants should apparently be considered optimal: on the one hand, intensive water exchange contributes to the production of calcium carbonate, and on the other hand, when the waves recede, the plants receive maximum sunlight (V. Kosmynin).

These hermatypic organisms raise the ridge above the level of the reef platform. At a distance of several meters from the edge of the outer slope there was usually a second, less pronounced ridge. It is obvious that previously the edge of the reef passed along this line, but due to the development of the current generation of the spur system, it ended up in the immediate rear.

Since both ridges are located on a horizontal plane, they should be considered in the structure of the rifflet, but the genesis of different parts of the reef platform itself is not the same. If its seaward part arises as a result of the active growth of corals and algae, then the areas lying closer to the shore owe their origin to the accumulation and partial cementation of clastic material, formed mainly on the outer slope and ridge and transported from there by waves.

So, on the reef, two main parts should be distinguished - the external, bioconstructional, created as a result of the life activity of hermatypic organisms, and the internal, accumulative, formed by the accumulation of material that comes from its external part. B.V. Preobrazhensky notes (1979) that the first is populated primarily by producers, i.e., producers of organic matter, while the other serves as the main place of settlement for consumers - consumers of finished organic substances.

The accumulative part of the rifflet, in turn, consists of three belts, or zones. The highest of them, closely adjacent to the shore, lies near the boundary of the upper water level at high (tropical) tides. It is represented by ancient limestone and covered with a layer of pure coral sand. This is the beach area. Directly adjacent to it from the sea is a strip of riffle, covered with large and small coral fragments that are not interconnected. The fact is that this high-lying part of the reef platform dries out every day for a long time and within its boundaries the calcareous algae that cement the fragments can no longer exist. There are no living corals here either. Between this dead zone of the riffle and the ridge extends a more or less wide living zone, in which individual massive corals take root, and a special fauna of lagoonal corals develops in the pools and pools on the silty bottom. There are both solitary mushroom corals and many finely branched bushy forms. As they die, they become cemented and also become part of the structure of the platform, but the latter is still primarily formed from fragments that fall here from the reefrock.

Thus, the lagoon reef, so different from the surf reef, is genetically closely related to it and arises from the interior of the latter.

Having studied a large number of coral reefs, we came to the conclusion that all the diversity of their geomorphological types can be reduced to a combination in different proportions of the main elements that make up the characteristic surf fringing reef.

Depending on the strength of the waves and the bottom profile, reefs of various types appear.

Coral islands are created by organisms (polyps) capable of secreting a calcareous substance. They live in colonies. New developing organisms remain in connection with dead ones and form a common trunk. For the life of corals, and, consequently, for the formation of an island, certain favorable conditions are needed. It is necessary that the water temperature does not drop below 20° on average. Therefore, polyps can only develop in warm tropical seas, and even then not everywhere. Where the coasts are washed by cold currents, there are none, as, for example, off the coast of Peru. In addition, most polyps require a solid bottom to take root and are relatively pure water; As a result, in those places where rivers flow into the sea, bringing with them turbidity, the reef is interrupted. Coral structures can be divided into two categories. The first category includes coral reefs fringing an island or continent - these are coastal and barrier reefs. The second category includes independent islands, known as atolls. Atolls have a more or less round or oval shape; less commonly, a triangular or quadrangular shape is found. A coastal reef fringes an island or the shore of a mainland. This shaft barely rises above the water, but even then it is not everywhere, and for the most part it is a shallow, since corals in general can only live under water. Living corals can exist at depths of up to 90 m, but at such depths they are quite rare, and for the most part they do not fall below 30-40 m. The low tide boundary is their upper limit. But some polyps can be exposed from under the water and be exposed to insolation for a short time. A number of processes lead to the rise of the coral shelf. The sea runs onto the shore, tears off pieces of polypnyak, crushes them into sand and throws them aground, filling up the voids; other organisms settle on the surface of the reef - mollusks, crustaceans, shells and skeletons of which, in turn, go to increase the reef. In addition, warm water dissolves limestone, and wind and waves throw substances brought from the shore aground. As a result, the reef as a whole becomes denser and sometimes rises somewhat above the sea surface, separated from the shore by a narrow channel. A barrier reef is much further from the shore than a coastal reef. Between it and the shore there is a lagoon, in some places also filled with reefs and sediment. The largest barrier reef stretches along the north-eastern coast of Australia for 2000 km. The width of the lagoon here is 40-50 km, sometimes it expands even to 180 km; Its depth in some places reaches 100 m, so steamboats can enter the lagoon, although swimming is dangerous, as there are many coral shoals. The width of the reef itself is several tens of kilometers. If we look at a map of the Pacific Ocean, we will see how a large number of barrier reefs are found there. All the large islands and a lot of small ones are fringed with coral buildings.

The third group of coral structures is represented by atolls. Actually, the entire ring of atolls is a shoal, and the islands rise out of the water only in places. The atolls make a very strong impression. Darwin also says: “It is difficult to imagine, without seeing with your own eyes, the infinity of the ocean and the fury of the waves in sharp contrast to the low border of land and the smooth surface of light green water inside the lagoon.” If there is a significant break in the atoll's ring, then ships can find a calm haven in its lagoon.

In cross-section, the atoll first appears as a steep slope, then as a flat shoal with islands rising on it, and finally as a deepening of the lagoon. The sizes of the atolls vary greatly: from 2x1 km to 25x10 km and even 90x35 km. The emergence of atolls can be explained as follows: if there is a shoal in the sea, barely covered with water, then if the bottom is hard, corals can settle on it and form an atoll. The atoll gets its oval shape because corals settle mainly along the edges of the shallows, since the sea waves here, if they are not excessively strong, and sea currents bring food supplies unhindered (Figure 5). A strand can arise either as a result of the rising of the seabed, or as a result of the formation of an underwater volcano, or as a result of the compaction of ash on a cone that barely rises above the surface. If initially the corals settle evenly over the entire surface of the shallows, then soon the marginal corals will find themselves in a more advantageous position: food is easily delivered to them, and they grow faster than the corals located in the middle. A lagoon is created in the middle, although it is quite shallow, since the shoal is not deep under water. The thickness of such a polypnyak is small and rarely reaches 10 m. Such formations are called coral reefs. It is more difficult to explain the origin of atolls among deep sea. Darwin, like many other scientists, noticed that coral islands often rise very steeply; their slope reaches 30°. At first it was believed that only coral islands had such steep slopes, but now we know that volcanic and sometimes continental islands are not inferior to them in this regard. Another fact that makes it difficult to explain the origin of atolls is that dead polypnyak is sometimes found at depths of 100-200 m or greater, and we know that corals cannot live at such depths.

All these difficulties were eliminated by Darwin's theory of reef formation, which linked all three types of coral formations together. He believed that every polypnyak begins its existence in the form of a coastal reef, then turns into a barrier, and then turns into an atoll, and that this transformation is determined by the subsidence of the seabed in a given area. Corals begin their construction around an island, most often of volcanic origin, and first form a coastal reef.

As the island slowly sinks, the lower parts of the polypnyak die, and new corals multiply above them, which manage to build on the reef. At the same time, the distance between the outer edge of the reef and the bedrock shore increases, and a barrier reef is formed. A small part of the island still remains, rising among the lagoon. Then further subsidence occurs and an atoll is formed; The island has already completely disappeared under water, and in its place there is a lagoon.

Naturally, with such an atoll formation, its outer slopes are steep. Many scientists recognized this theory, especially developed in detail in 1885 by Deng, but then objections were raised against it. Darwin's theory was argued against by the fact that often in the same group of islands we encounter all the transitional stages of reefs. Thus, in a group Caroline Islands There are coastal reefs, nearby barrier reefs and atolls, from the lagoons of which small islands still peek out, and, finally, typical atolls (Figure 6).

mainland volcanic coral island

Figure 5. - Scheme of attol formation.

However, this objection, based on the existence of different forms of reefs in proximity to each other, is easily eliminated if it is assumed that in this place uneven vertical movements of the seabed occurred. Thanks to this, various forms of polypnyaks could form nearby. The Darwinian theory is also supported by the fact that although sometimes different forms of reefs are found in the neighborhood, much more often one form dominates over vast areas, as is, for example, observed in Oceania. Drilling a polyppyak on the island of Funafuti (in the Ellis Islands group) also confirmed the correctness of Darwin's views. The well penetrated 334 m in a continuous polypnyak.

Consequently, in this place there was a real sinking of the bottom, since corals cannot live at such a depth.

Figure 6. - Caroline Islands.

According to the observations of Murray, Guppy and Agassiz, there is no need for an atoll to develop necessarily from a coastal and barrier reef - it can arise independently, moreover, not only in shallow water, but also in the deep sea. If at the bottom of the sea happens volcanic eruption, then corals can create an atoll on the edge of an emerging underwater volcano, around its crater. Already Chamisso, during his trip to Oceania, pointed out that the formation of a lagoon is often due to the fact that the crater of a volcano serves as the bottom of the lagoon. Sometimes the underwater hill lies very deep, at a depth of several hundred meters. Corals cannot live at such a depth, but many other organisms can exist there: crustaceans, mollusks and algae that have a calcareous skeleton; the skeletons of these organisms increase the height of the underwater reef, so that corals can eventually settle on it (Murray's theory). As for the formation of the lagoon, Agassiz believed that sea tides contributed to its deepening. The atoll does not represent a closed ring, but has breaks. The tidal current penetrates them, produces a strong eroding effect and clears the lagoon of sediment. Despite the objections and additions made, Darwin’s theory has generally been fully confirmed by the latest research, and can be considered the most correct explanation of the origin of atolls.

This reef, in fact, is represented by only one component element, namely the outer slope with a ridge at the top. In this place, the coastal cliffs go steeply into the sea, and hermatypic corals develop on them. The fragments of these corals, which inevitably arise as a result of the action of the run-up and during storms, due to the steepness of the cliffs rising from the sea, do not accumulate at the top, but roll down the slope.

Their accumulations are visible at a depth of about 20 m, where the flat bottom begins. Only in certain areas behind the reef crest can you find small (no more than 3-5 m wide) areas - the beginnings of a future rifflet.

Unlike surf reef corals, lagoon species are able to remain dry for several hours during low tide. The waves in the lagoon are weaker, and in low water the water does not fall on the exposed corals.

Sometimes it is completely separated from the ocean by a ring reef, and sometimes it is connected to it by a wide strait, sufficient for the passage of boats and even ships. There is a lot of fish, edible shellfish, crayfish, algae; In some places there are sea turtles and dugongs.

Lagoons and channels between reefs and land are often used as safe harbors, hydrodromes and bases for ships and submarines.

Corals also cause a lot of trouble: reefs are difficult to notice from afar; they suddenly appear in front of the ship; since the depth near them sharply drops, and directions and maps of coral areas very quickly become outdated. Therefore, many ships suffered accidents near the reefs.

Interesting case happened to the famous Captain J. Cook during his first trip around the world. On June 11, 1770, not far from the Great Barrier Reef, the frigate Endevre suddenly ran into a coral reef. Only a day later, having completely unloaded the ship, it was possible to remove it from the reef and take it to the mouth of the river, where the Australian city of Cooktown now stands. During repairs, Cook discovered that the main hole in the ship's hull was almost completely sealed with a large coral fragment. This circumstance helped save the ship.

The economic importance of all coral islands is small; Their population is also small: before the Second World War, about 100 thousand people lived here. From here they export copra - the core of coconuts and sea cucumbers; mother of pearl, mainly from pearl oyster shells. Pearls are also mined here. On a small atoll off the west coast of Australia in 1917, one of the most beautiful pearls in the world, the Star of the West, was found. It is the size of a sparrow's egg and is valued at £14,000.

Coral limestone is used here and there as a building material; when ground, it is used to polish wood and metal. In Ceylon, cement is produced from it. Madrepore corals, like red ones, are used to make everyday items, jewelry, vases, etc. They are also used in Chinese medicine.

In addition to corals with a calcareous skeleton, there are also corals with a horny skeleton. In Indochina and Malaya, for example, gorgonine, the horny substance of black coral, is used to make decorations for rooms, weapons, knife handles, beads, and bracelets.

Small size, remoteness from continents, endemicity and poverty of biological diversity of flora and fauna create very big problems in cases of irrational use natural resources, serious disturbances of ecological balance and intensive environmental pollution. After all, the ecosystems of these islands were formed for a long time in conditions of limited connections with other islands and the mainland. Therefore, it is very difficult to restore damaged ecosystems here. The nature of atolls is especially vulnerable, firstly, due to their very small size. Secondly, due to the instability of their ecosystems, the primitiveness of connections between organizations and the presence of ecological niches that allow organisms alien to island landscapes to invade. Thirdly, due to the limited resources on the atolls fresh water, which significantly limits the possibilities of economic activity. Therefore, most of the atolls are sparsely populated or do not even have a permanent population, but are used for seasonal work on coconut plantations.

Conclusion

Islands are small isolated areas of land. The area of ​​the islands is 9.9 million km 2, about 78% of this area is 28 large islands. Of these, the largest is Greenland.

Groups of islands are called archipelagos. They can be compact, such as Franz Josef Land, Spitsbergen, Greater Sunda Islands, or elongated, such as Japanese, Philippine, Greater and Lesser Antilles. In Russian, such islands are called ridges (Kuril Ridge). Archipelagos of small islands scattered in the Pacific Ocean are united into three large groups - Melanesia, Micronesia and Polynesia.

By origin, all islands can be grouped as follows:

• A) Mainland: platform, continental slope, orogenic, island arcs, coastal:
  • - skerries,
  • - fjord,
  • - braids and arrows,
  • - deltaic.
• b) Independent:
  • 1 Volcanic:
    • - fissure effusion,
    • - central effusion,
    • - panel and conical,
• 2 coral:
  • - coastal reefs,
  • - barrier reefs,
  • - atolls.

Mainland Islands are genetically connected with the continents, but these connections are of a different nature and this affects the nature and age of the islands, their flora and fauna.

Platform islands lie on a continental shelf and geologically represent a continuation of the mainland. Islands of the continental slope are also parts of the continent, but their division occurred earlier. They are usually separated not by a gentle bend of the continent, but by a deep split. The straits between the island and the mainland are of an oceanic nature. The flora and fauna of such islands is very different from the mainland. This group includes Madagascar and Greenland. Orogenic islands represent a continuation of the mountain folds of the continents. Island arcs- parts of transition areas. Mainland offshore islands.

Independent islands have never been parts of continents and in most cases formed independently of them.

Volcanic Islands- the main mass of volcanic islands is formed by eruptions of the central type. Naturally, these islands cannot be very large.

encyclopedic Dictionary- coastal reefs, barrier reefs and lagoon islands. Coastal reefs begin directly offshore. Barrier reefs are located at some distance from land and are separated from it by a strip of water - a lagoon.

Atolls (lagoon islands) are located in the ocean. These are low islands in the shape of an open ring or ellipse. Inside the atoll there is a lagoon less than 100m deep. The island is composed of sandy or pebble-block material - products of coral destruction. The bottom of coral lagoons is flat, covered with coral sand or accumulations of calcareous algae remains.