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Gilbert Islands, Marshall Islands, neutralization of Truk base, first attacks on the Marianas - June 1943 - April 1944

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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 that were taken for islands (“lands”) are melting, sea spits 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).

The 28 largest islands in the world include the following:

1.Greenland

2. New Guinea

3.Kalimantan (Borneo)

4. Madagascar

5. Baffin's Land

6.Sumatra

7.UK

9.Victoria (Canadian Arctic Archipelago)

10. Ellesmere Land (Canadian Arctic Archipelago)

11.Sulawesi (Celebes)

12. South Island of New Zealand

14.North Island of New Zealand

15. Newfoundland

18. Iceland

19. Mindanao

20. New Earth

22. Sakhalin

23. Ireland

24.Tasmania

25.Banks (Canadian Arctic Archipelago)

26. Sri Lanka

27. Hokkaido

Both large and small islands are located either singly or in groups. Groups of islands are called archipelagos. Archipelagos can be compact (eg Franz Josef Land, Svalbard, Greater Sunda Islands) or elongated (eg Japan, Philippines, Greater and Lesser Antilles). Elongated archipelagos are sometimes called ridges (for example, the Kuril ridge, the Aleutian ridge). The archipelagos of small islands scattered across the expanses of the Pacific Ocean are united 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) coastal islands: a) skerries, 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 of 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 of the Mediterranean Sea are branches of the Alpine folds. The archipelago of New Zealand is also of orogenic origin.

island arcs garlands border East Asia, America and Antarctica. The largest region of island arcs is located off the coast of East Asia: the Aleutian ridge, the Kuril ridge, the Japanese ridge, the Ryukyu ridge, the 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: the Tierra del Fuego archipelago, the Falkland Islands, etc. Tectonically, all island arcs are confined to modern geosynclines.

Mainland offshore islands have different origins and represent different types of 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 large islands, which are not inferior in size to 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 of the 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 (for example, the 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. These are 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.

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.

An island is a piece of land that is washed on all sides by water - ocean, sea, lake or river. In the case of the ocean, the island is smaller than the mainland.

With the separation of land and waters of the oceans, islands arose. These are areas of land that rise above the surface of the water that surrounds them. Their number is constantly changing - some islands rise from the abyss, others sink under water, ceasing to exist. Some islands are in splendid isolation in the middle of the expanses of water, others are united in companies - groups. If the islands of the group are close to each other and stand on a common underwater basis, in this case they are called archipelago. Such, for example, are Svalbard, the Kuril Islands, Franz Josef Land, the Aleutian Islands, the Greater and Lesser Antilles, and other island groups.

Freshwater islands

Let us immediately separate the islands located in freshwater reservoirs - lakes and rivers - from ocean and sea ones. Lake islands are formed as a result of sedimentation, tectonic processes (bottom uplift), volcanic activity, or changes in water levels. An example of a well-known lake island is Lindau Island, on which one of ancient cities Germany, which is the namesake of the island. Lindau is located on Lake Constance.

River islands are formed in the channel, more often in the lower reaches, where the current is smoother. Distinguish between alluvial and floodplain river islands. The stream carries sand, small pebbles, clay, which are deposited over time, forming an island. Floodplain islands are separated by formed separate branches in the main channel of the river. The largest river island in the world is Bananal, located on the Araguaia River in Brazil.

Salt water islands are divided into continental (continental) and oceanic. mainland islands- These are areas of land that are part of the mainland. They lost contact with him as a result of lowering the surface of the earth or raising the level of the ocean. They are located on the shallows that connect them to the mainland, separated from it by straits or shelf seas. The depth of the seas lying between them is small. usually does not exceed two hundred meters. Such islands separated from the mainland relatively recently. For example, the British Isles became isolated in the Anthropogen, with rising sea levels due to melting glaciers. Sometimes the mainland islands are a continuation of the mountain range. For example, the island of Sakhalin is a continuation of the Far Eastern mountainous country, the island of Novaya Zemlya is a continuation of the Urals, the island of Tasmania is a continuation of the Australian Alps. And sometimes sea currents deposit sand deposits on the shelf, eventually forming an island.

continental islands separate from parent continent deep seas, with depths of hundreds, and often thousands of meters. Such islands may be part of existing continents or the remnants of long-vanished ones. They separated from the continental plates long ago, millions and tens of millions of years ago, usually as a result of a sharp subsidence of a land area and flooding it with ocean waters. In this case, not a gentle depression is formed, but a stepped failure. Continental islands arise when the earth's crust breaks, when a plume rises and rifts form. The earth's crust above the plume is cracking. If the ocean is nearby, the breakaway piece of land is squeezed into it and an island is formed. This is how Madagascar was born.

oceanic islands are not connected to the continents in any way and are located on the oceanic crust. They can be formed as a result of the activity of a volcano and then they belong to the group of volcanic. Or as a result of the work of marine organisms - polyps-corals - and, accordingly, are included in the category of coral islands. But - in order.

Volcanic islands

They are formed when an erupting volcano increases the height of its cone with erupting lava, eventually rising more and more above the sea surface. Similar processes are usually observed at the boundaries of lithospheric plates. By total area created by volcanoes islands larger than Europe.

There are enough representatives of this species among the islands. These include Iceland, Kunashir (the largest in the family Kuril Islands), Easter Island, White Island in New Zealand (pictured). The volcano also created the notorious Krakatau in the group of the Greater Sunda Islands. In the Mediterranean Sea of ​​volcanic origin, the island of Sicily, with famous volcano Etna "on board". There are about four thousand islands of similar origin in Japan, and people live on some of them.

But active volcanoes they know how to create completely different islands, where their labor is used only for initial stage formations. And then marine organisms get down to business, equipping everything to their liking in their new home.

coral islands

The foot of the calmed volcano is found by coral polyps to be very suitable for the construction of their dwellings and are actively developing this, for the time being, free territory. Each new generation of these animals builds its own calcareous formations on buildings of the past generation. The lower layers of buildings under the weight of the upper ones are compacted, forming coral reef. In height, such a colony is up to fifty meters.

As time goes by, as a result of erosion or collapse of the walls of the volcano, it hides under water. And the corals remain, forming a ring of reefs. Its outer side is constantly receiving new portions of nutrients from the ocean, and the polyps located there are happily growing. But the inhabitants of the inner side are less fortunate, there is little food and they stop development. A lagoon filled with water is formed. Sometimes the ring can be open, sometimes solid. Such an island is called an atoll. In diameter, it usually ranges from 2 to 90 kilometers. Over time, the lagoon fills with alluvial sand and the remains of marine organisms. It turns out the island. For example, the islands of the Maldives (pictured), Marshall Islands, Tuamotu Island, Bikini Atoll have a similar origin. All of them are in warm seas who love coral polyps.

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