How the mainland islands arise briefly. Mainland Island - what is it? Definition, types and examples. About the islands and their origin

Large and small islands formed - land areas in the sea, ocean, lake, river, surrounded on all sides by water. The area of ​​all the islands of the planet is 9.9 million km2, which is equal to the area. However, this figure is approximate, as total number Islands are constantly changing: some islands appear, others disappear. About 79% of all island land falls on 28 large islands. Of these, the largest -.

The islands are located singly or in groups. Groups of islands lying at a short distance from each other and having a common underwater base are called archipelagos (, Svalbard, Aleutian, Japanese, Greater and Lesser Antilles).

By origin, all the islands can be divided into groups:

mainland islands.These are separated parts of the mainland, similar to it in and. They are separated from the main land mass by straits or shelf seas (, Canadian Archipelago). Many mainland islands are a continuation of the mountain folds of the mainland. So, - one of the folds of the Far Eastern mountain country; - continuation ; - . The time of formation of these islands is different.

Volcanic islands.These are independent islands, they have never been part of the mainland. there are islands in all oceans, with the exception of. The largest island on Earth volcanic origin- . Many volcanic islands appeared during the spreading of lava. This group includes such islands as the Hawaiian archipelago, Ascension Island.

The typical form of which is atolls. This ring island in the form of a narrow ridge, continuous or broken, surrounding a shallow and well-heated lagoon. The chief builder of these islands giant size are small marine inhabitants - coral polyps. They extract from sea ​​water lime and build shell houses from it, which, when joined together, form straight vertical columns or coral thickets similar to dense shrubs. These tiny animals live shallow, because they love warm clear water, - either off the coast or on the tops of seamounts. Having lived their short life, the corals die, and new polyps erect their thickets on the empty houses. Under the weight of the upper buildings, the lower ones are compressed, forming a solid foundation. Centuries pass, and on this foundation there are chains of coral rocks - reefs. If coral buildings were erected along the edges of a round crater underwater volcano, then an island is formed, having the shape of a ring with a lagoon in the middle. In it, the ocean water, which enters here at the time, acquires a surprisingly pure azure color, which creates a special charm for which the atolls are famous.

Most coral structures (reefs and atolls) are found in warm waters and, they are often found in entire archipelagos. Atoll islands can be from 2 to 90 km across.

Coral structures provide convincing evidence that some areas of the ocean floor are rising and others are sinking. If the ocean floor were motionless, then the height of such buildings would not exceed 50 meters. But studies prove that they often reach a thickness of many hundreds of meters and are located at depths up to 1600 m. The only reason for such an arrangement of these structures may be the sinking of the ocean floor, along with which the entire coral structure sinks. Thanks to this, the upper, youngest parts of the buildings get the opportunity to gradually build on. In other places, coral structures rise tens of hundreds of meters above sea level. This means that the seabed has risen in these areas.

1. General characteristics.

2. Biomes of mainland islands.

3. Biomes of oceanic islands.

1. General characteristics. The biotas of the islands of the seas and oceans are extremely diverse. Closely related to the conditions for the formation of the islands themselves, however, they do not have a single feature that would be characteristic of all the islands without exception. The diversity of the island's biota depends on its origin, age, size, distance from the mainland and its natural conditions.

By origin islands in the seas and oceans are divided into two main groups - mainlandAndoceanic.

Mainland represent a part of the continent separated in one or another geological epoch. They protrude above the water level within the underwater margin of the continents and are usually composed of bedrock (Great Britain, Greenland, Madagascar, New Zealand, New Caledonia, Hawaiian, etc.). Small ones can be formed as a result of the accumulative activity of waves and surf.

oceanic islands distributed within the ocean floor and on mid-ocean ridges. These include coral (atolls and reefs) and volcanic islands (Galapagos, Kerguelen, Mascarene, Canary, Easter, etc.).

Between these two groups of islands, continental and oceanic, there are intermediate forms - geosynclinal islands, or islands of the transition zone and island arcs. They are the most diverse natural conditions and have a more complex structure of landscapes - from flat to mountainous areas. As a rule, all geosynclinal islands form into archipelagos or form island arcs (Great Sunda, Philippine, Japanese, etc.).

By complexity of ecosystems islands can be low, including biogenic (atolls, reefs and mangroves) and shelf, and high (volcanic, geosynclinal and continental slope, or shelf). High islands, in turn, may have weak or well-defined altitudinal zonality.

Conditions for formation of biota on continental and oceanic islands is completely different.

1. The mainland islands separated from the continents with the species diversity of vegetation and animal population that was inherent in this part of the continent.

2.Oceanic islands were inhabited only by organisms capable of overcoming large expanses of water. In the first case, the type of biota formation can be defined as relict, in the second, as immigration.

2. Biomes of mainland islands. On islands of mainland origin, the biota gradually evolved over time. impoverished by extinction parts of forms and even species. The extinction of the species can be explained by its small number at the time of the separation of the island from the mainland, which does not ensure long-term existence in conditions isolation. Moreover, the death of the species inherited by the island is not compensated by the appearance of immigrants who enter the island, as a rule, in a limited number of individuals and do not always survive.

The gradual extinction of species on the islands can be judged from the fact that small islands of continental origin, in contrast to large ones, have almost purely oceanic fauna. So, among the Pearl Islands on big island Rei is inhabited by about 1/3 of continental species, and on the small island of Kondator - only 1/10 (Voronov, 1987). If two islands of different sizes separated from the mainland at the same time, then the original biota can be almost completely preserved on the larger one and completely or partially disappear on the smaller one.

Patterns of the location of the continents

1. Most of the land is located in the Northern Hemisphere. The northern hemisphere is continental, although even here land accounts for only 39%, and about 61% for the ocean.
2. The northern continents are quite compact. southern continents are very scattered and scattered.

3. The relief of the planet is anti-semitic. The continents are located so that each of them on opposite side Earth certainly corresponds to the Ocean. This is most obvious in comparison arctic ocean and Antarctic land. But if the globe is set so that at one of the poles there is any of the continents, then at the other pole there will definitely be an ocean. There is only one minor exception: the ending South America antipodal southeast Asia. Antipodality, since it has almost no exceptions, cannot be an accidental phenomenon. It is based on the balance of all parts of the surface of the rotating Earth.

In the process of the development of the earth's crust and its interaction with the World Ocean, large and small islands were formed. The total number of islands is constantly changing. Some islands appear, others disappear. For example, deltaic islands are formed and eroded, ice massifs are melting, taken for islands (“lands”), sea ​​braids acquire an island character and, conversely, the islands join the land and turn into peninsulas. Therefore, the area of ​​the islands is calculated only approximately. It is about 9.9 million km 2. About 79% of all island land falls on 28 large islands. Of these, the largest is Greenland (2.2 million km 2).

Among the 28 largest islands the globe includes the following:

1.Greenland
2. New Guinea

3.Kalimantan (Borneo)

4. Madagascar
5. Baffin's Land

6.Sumatra
7.UK
8. Honshu
9.Victoria (Canadian arctic archipelago)

10. Ellesmere Land (Canadian Arctic Archipelago)

11.Sulawesi (Celebes)

12. South Island of New Zealand

13. Java
14.North Island of New Zealand

15. Newfoundland
16. Cuba
17.Lucon
18. Iceland
19. Mindanao
20. New Earth

21. Haiti
22. Sakhalin
23. Ireland
24.Tasmania
25.Banks (Canadian Arctic Archipelago)

26. Sri Lanka
27. Hokkaido
28. Devon

Both large and small islands are located either singly or in groups. Groups of islands are called archipelagos. Archipelagos can be compact (for example, Franz Josef Land, Svalbard, Greater Sunda Islands) or elongated (for example, Japanese, Philippine, Greater and Lesser Antilles). Elongated archipelagos are sometimes called ridges (for example, Kuril ridge, Aleutian Ridge). archipelagos small islands scattered across the expanse Pacific Ocean, combined into the following three large groups: Melanesia, Micronesia (Caroline Islands, Mariana Islands, Marshall Islands), Polynesia.

By origin, all the islands can be grouped as follows:

I. Mainland Islands:

1) platform islands,

2) islands of the continental slope,

3) orogenic islands,

4) island arcs,

5) offshore islands: a) skerry, b) Dalmatian, c) fjord, d) spits and arrows, e) delta.

II. Independent islands:

1. volcanic islands, including a) fissure lava outpouring, b) central lava outpouring - shield and conical;

2. coral islands: a) coastal reefs, b) barrier reefs, c) atolls.

mainland islands genetically related to the continents, but these connections are of a different nature, which affects the nature and age of the islands, their flora and fauna.

platform islands lie on the continental shelf and geologically represent a continuation of the mainland. The platform islands are separated from the main land mass by shallow straits or shallow straits. Examples platform islands are the following: British Isles, Svalbard archipelago, Franz Josef Land, Severnaya Zemlya, New Siberian Islands, Canadian Arctic Archipelago.

The formation of straits and the transformation of part of the continents into islands date back to recent geological time; therefore, the nature of the island land differs little from the mainland.

Islands of the mainland slope are also parts of the continents, but their separation occurred earlier. These islands are separated from the adjacent continents not by a gentle trough, but by a deep tectonic fault. Moreover, the straits are oceanic in nature. The flora and fauna of the islands of the continental slope is very different from the mainland and is generally insular in nature. Examples of continental slope islands are the following: Madagascar, Greenland, etc.

Orogenic islands are a continuation of the mountain folds of the continents. So, for example, Sakhalin is one of the folds of the Far Eastern mountainous country, New Zealand is a continuation of the Urals, Tasmania is the Australian Alps, the islands mediterranean sea- branches of alpine folds. The archipelago of New Zealand is also of orogenic origin.

island arcs garlands border East Asia, America and Antarctica. Most large area island arcs are off the coast East Asia: Aleutian ridge, Kuril ridge, Japanese ridge, Ryukyu ridge, Philippine ridge, etc. The second region of island arcs is located off the coast of America: the Greater Antilles, the Lesser Antilles. The Tritium Region is an island arc located between South America and Antarctica: an archipelago Tierra del Fuego, Falkland Islands and others. In tectonic terms, all island arcs are confined to modern geosynclines.

Mainland offshore islands have different origins and are different types coastline.

Independent islands have never been part of the continents and in most cases formed independently of them. The largest group of independent islands are volcanic.

Volcanic islands are found in all oceans, especially in the areas of mid-ocean ridges. The size and features of volcanic islands are determined by the nature of the eruption. Fissure outpourings of lava create major islands, not inferior in size to the platform ones. The largest island of volcanic origin on Earth is Iceland (103 thousand km 2).

The main mass of volcanic islands is formed by eruptions central type. Naturally, these islands cannot be very large. Their area depends on the nature of the lava. The main lava spreads over long distances and forms shield volcanoes 9 for example, Hawaiian Islands). The eruption of acidic lava forms a sharp cone of a small area.

Coral islands are waste products of coral polyps, diatoms, foraminifera and other organisms. Coral polyps are quite demanding on habitat conditions. They can live only in warm waters with a temperature of at least 20 0 С, therefore coral buildings are common only in tropical latitudes and go beyond them only in one place - Bermuda washed by the Gulf Stream.

Depending on their location in relation to modern land, coral islands are divided into the following three groups:

1) coastal reefs,

2) barrier reefs,

3) atolls.

coastal reefs begin directly at the coast of the mainland or island in the low tide and border it in the form of a wide terrace. Near the mouths of rivers and near mangroves, they are interrupted due to low salinity of the water.

barrier reefs located at some distance from land, separated from it by a strip of water - a lagoon. The largest reef at present is the Great Barrier Reef. Its length is about 2,000 km; the width of the lagoon ranges from 35 to 150 km at a depth of 30-70 m. Coastal and barrier reefs border almost all the islands of the equatorial and tropical waters of the Pacific Ocean.

atolls located among the oceans. This - low islands in the form of an open ring 100-200 m; the diameter of the entire atoll ranges from 200 m to 60 km and even more. Inside the atoll there is a lagoon up to 100 m deep. The depth of the strait between the lagoon and the ocean is the same. The outer slope of the atoll is always steep (9 to 45 0) and falls to a depth of hundreds of meters, and sometimes more than a kilometer. The slopes facing the lagoon are flat and inhabited by a variety of organisms.

The genetic relationship of the three types of coral structures is still an unresolved scientific problem. According to Charles Darwin's theory, barrier reefs and atolls are formed from coastal reefs with the gradual subsidence of islands. At the same time, the growth of corals compensates for the lowering of its base; a lagoon appears on the site of the top of the island, and the coastal reef turns into a ring atoll.

Oceania is the name of the largest cluster of large and small islands on our planet in the western and central Pacific Ocean. The islands of Oceania occupy about 1.3 million square kilometers of the Earth's surface and there are almost 7 thousand of them, large and small.

Regions of the islands of Oceania

Traditionally, the islands of Oceania are divided by geographers, historians and ethnographers into three groups: Melanesia with the most big island New Guinea, Micronesia, Polynesia with the second largest island in Oceania, New Zealand.

The region of the islands of Oceania Melanesia ("black island")

Melanesia is located in the west of Oceania and, in addition to New Guinea, it includes the Bismarck and Louisiade archipelagos, as well as the islands of D "Anrtkastro, the Santa Cruz Islands, Solomon islands, New Herbid Islands, New Caledonia, Fiji Islands, Loyalty and several others.

The main part of the territory of Melanesia falls on the island of New Guinea. He owns 829 of the 969 thousand square kilometers occupied by this area of ​​the islands of Oceania.

Region of the islands of Oceania Polynesia ("multi-island")

Polynesia stretched from the southwest to the east of Oceania. The largest islands of Polynesia are New Zealand, Hawaii, Tonga, Samoa, Wallis, Tokelau, Horn, Cook, Tuvalu, Tubuai, Societies, the Marquesas Islands and Easter Island.

265 thousand square kilometers of the total area of ​​Polynesia falls on New Zealand, 17 thousand on the Hawaiian Islands and 9 thousand on all the rest.

Ocean Islands Region of Micronesia ("small islands")

Micronesia is located in the northwest of Oceania. total area its islands are only 2.6 thousand square kilometers, but these tiny islands are scattered over an ocean area of ​​\u200b\u200babout 14 million square kilometers.

The main island groups of Micronesia are the Marshall, Caroline and Mariana Islands, as well as the Gilbert Islands.

Islands of Oceania by type of origin

The islands of Oceania differ in their origin and on this basis they are usually divided into four types: volcanic, coral or atoll (biogenic), continental, and also geosynclinal.

Volcanic islands of Oceania

The volcanic islands of Oceania are the peaks of dormant or active underwater volcanoes. Among them there are islands ranging from ten square kilometers to several thousand and they are the main type of islands in Oceania.

The most famous of the volcanic islands are the Hawaiian Islands, Easter Island, Tahiti and Samoa.

Coral islands of Oceania (biogenic)

Entire colonies of small marine animals - corals - usually settle in the oceanic shallow water. For centuries, when corals die, their skeletons cover the bottom of the ocean, are pressed and form rock. Over time, above the surface of the water appear Coral reefs and entire islands, and if coral deposits occurred along the contour of the mouth of an underwater volcano, then atolls appear - coral islands with a lagoon in the center.

There are hundreds of coral islands (atolls) in Oceania, both single and forming entire archipelagos. These are the Caroline, Mariana, Marshall Islands, as well as the Gilbert and Tuamotu Islands. The largest atoll in Oceania is Kwajalein. The area of ​​​​its territory is 2.3 thousand square kilometers (including the area of ​​​​the lagoon) and it belongs to the Marshall Islands archipelago.

Mainland islands of Oceania

The mainland islands of Oceania were once part of the mainland and became islands as a result of the movement of the earth's crust. So New Guinea Australia is separated from the mainland only by a strait, the bottom of which until recently was dry land, and New Zealand is part of the huge mainland that once existed, which included both Australia and Antarctica.

The mainland islands of Oceania account for 90% of its territory. They have both lowlands and mountain systems, and long mountain plateaus.

MAINLAND ISLANDS

Land areas that once formed part of the continents, then separated from the latter. At the same time, the continents themselves either still exist, or have long disappeared.

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"MAINLAND ISLANDS" in books

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