What are mainland islands. Regions of the islands of Oceania. Volcanic islands of Oceania

An island is considered to be a piece of land, as a rule - natural origin, which is surrounded on all sides by water, the island must constantly rise above the surface of the water, even during periods of high tide. Islands and groups of islands differ from the continents in smaller sizes, there are both single islands and their groups - called island archipelagos.

mainland islands

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

1) platform, 2) continental slope, 3) orogenic, 4) island arcs, 5) coastal: a) skerries, b) Dalmatian, c) fjord, d) spits and arrows, e) delta.

Independent islands:

1) volcanic - a) fissure outpouring of lava, b) central outpouring of lava - shield and conical; 2) coral - a) coastal reefs, b) barrier reefs, c) atolls.

Origin , All islands divided into single, And islands in a group , which can be grouped as follows:

Mainland Islands:

Platform

Continental

Orogenic

island arcs

coastal

Independent islands:

1) volcanic - a) fissure outpouring of lava, b) central outpouring of lava - shield and conical;

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

mainland islands

They are genetically related to 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

They are located on the continental shelf and in the geological sense, they represent a continuation of the mainland. From the main land mass, such islands are separated from each other by shallow straits or shelf seas. Islands platform origin- these are the British Islands, Franz Josef Land, Severnaya Zemlya, Svalbard, New Siberian, Canadian archipelago. The formation of straits and the transformation of part of the continents into islands are of recent times, so the nature of island land differs little from that of mainland land.

continental islands

They are also parts of the continents, but their separation happened much earlier. Continental islands are usually separated - not by a gentle deflection of the mainland, but by a deep tectonic split. The straits are oceanic in nature. The flora and fauna of such islands is very different from the mainland flora and fauna. This group of islands includes Greenland, New Guinea and Madagascar. site/node/2826

Orogenic islands

They are a continuation of the mountain folds of the continents. So, to Sakhalin Island - this is one of the folds of the Far Eastern mountain country, and the island New Earth- continuation of the Urals, islands mediterranean sea- branches of alpine folds, Tasmania - Australian Alps, by the way, New Zealand also an orogenic island.

Island arcs border East Asia with garlands: Aleutian, Kuril, Japanese, Ryukyu, Philippine. The second section of the island arcs - Central America: Large and Small Antilles. The third section is an island arc between South America and Antarctica. Island arcs are the areas of the greatest activity of the Earth's crust of the present time. These are modern geosynclines.

Islands, or island groups located in fresh water oemah, are usually subdivided into alluvial and erosive islands.

Alluvial islands

They are formed as a result of accumulation of sediments in the channel or coastal zone of a reservoir (lake). Erosion islands arise, as a rule, as a result of flow around the remnant caused by bedrock or alluvium, and also due to the separation of a protruding section of water (lake-side) land.

Depending on the presence of the population on the islands, whether they are single or in a group, they are divided into inhabited and uninhabited islands.

About the islands and their origin

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.

Samoilov K.I. Marine vocabulary. - M.-L.: State Naval Publishing House of the NKVMF of the USSR, 1941

mainland islands

land areas separated from continents as a result of geological or hydrological processes.

Edwart. Explanatory Naval Dictionary, 2010

See what "MAINLAND ISLANDS" is in other dictionaries:

Areas of the mainland that have separated from it due to abrasion or the sinking of part of the land below sea level. To M. o. include naib. major islands of the world: Greenland, Kalimantan, Madagascar ... Natural science. encyclopedic Dictionary

Land areas surrounded on all sides by the waters of the oceans, seas, lakes, rivers. They differ from the mainland in relatively small sizes. There are single islands and their groups (archipelagos). Islands in the oceans and seas are divided into mainland ... ... encyclopedic Dictionary

- (Islands) small parts of the land compared to the continents, surrounded by the sea on all sides. By origin, the islands are divided into mainland, i.e., separated parts of the land, and original, never connected to the mainland, alluvial and oceanic ... ... Marine Dictionary

Land areas surrounded on all sides by the waters of oceans, seas, lakes or rivers. In the seas and oceans, there are single islands and groups (archipelagos). By origin, they are divided into continental (separated from the continents) and oceanic ... ... Marine Dictionary

Land areas surrounded on all sides by the waters of the ocean, sea, lake or river. They differ from the mainland in relatively small sizes. There are single O. and groups of O. Archipelagos. O. in the oceans and seas are divided into continental, ... ... Great Soviet Encyclopedia

O. are called relatively small areas of land, surrounded on all sides by water. They differ from the continents only in size, but the difference between the two is very conditional, since the ratio between the sizes of the penultimate largest ... ... Encyclopedic Dictionary F.A. Brockhaus and I.A. Efron Encyclopedic reference book "Latin America"

The mainland islands (examples will be given below) are part of the land that was previously part of the continent, and later separated from it. This occurs as a result of various hydrological or geological processes. As a rule, the mainland and the island have a fairly similar relief. They are separated by water areas, such as shelf seas and straits. The observation of scientists shows that the distance between the main landmass and the island can vary. This is due to the mobility of the earth's crust.

Islands of mainland origin are divided into several types. All of them are connected with their continents at the genetic level. However, despite this, the flora and fauna of such islands can differ significantly. So, let's look at the types of islands depending on the origin.

Platform mainland islands

The platform islands are, in fact, an extension of the continent. They lie on the continental shelf and are separated from the main landmass by various water areas, such as straits and seas. Islands have this origin. Canadian archipelago, Severnaya Zemlya, Svalbard and British. These land areas practically do not differ from the mainland in flora and fauna. And this is due to the fact that they were formed relatively recently.

Islands of the mainland slope

The second type is the islands of the continental slope. They are not much different from the first ones, but their break with the continent took place a little earlier. Unlike platform ones, their separation from the main land occurred due to deep tectonic splits, and not troughs, as in the first case. A mainland island of this type is separated from the continent by an oceanic strait. Prominent examples are Fr. Greenland and about. Madagascar.

Orogenic islands

The third type is orogenic islands. These land areas are formed from the continuation of the mountain folds of the mainland. These include New Zealand, Tasmania, Fr. Nova Zemlya, which, in fact, is a continuation Ural mountains. They are all orogenic mainland islands. Examples can go on and on. Sakhalin, which is a continuation of the Far Eastern mountain range.

island arcs

And finally, the most active view mainland islands - island arcs. They're in in large numbers are on the coast East Asia, Central America and between South America and Antarctica. These include the Japanese island arc, the Aleutian, the Philippine and others. It is worth noting that it is these land areas that are currently in the area of \u200b\u200bhigh activity of the earth's crust.

Peculiarities

Due to its remoteness from the main continent and complete isolation from other lands, the mainland island has a high level of endemic flora and fauna. The earlier it separated from the mainland, the more peculiar its plant and animal world. Islands such as Hawaii, Novaya Zemlya are located at a considerable distance from their continents. This led to the formation of more than 70% of endemics in the flora and fauna of these lands. Also, representatives of the animal world live on the islands, which have some deviations from the usual norms. For example, gigantism in reptiles and, conversely, island mammals are usually smaller than on the mainland. The first group includes Galapagos tortoises- they are extraordinary large sizes. The second includes different kinds hoofed animals.

tasmania island

The mainland island of Tasmania is separated from the mainland by Bass Strait. His geological structure and relief allow us to say that this is a continuation of the East Australian mountains. The island has a unique fauna. Animals from Antarctica are found here, as well as a number of some representatives that have long been destroyed on the mainland.

New Earth

The Novaya Zemlya archipelago is also classified by scientists as a continental type. The main islands are separated from each other by the narrow strait Matochkin Shar. Another archipelago is washed by the strait separating it from the island of Vaygach.

Sakhalin island

Sakhalin Island is a mainland island. Located at east coast Asia. It separates from Fr. Hakkaido, whose minimum width is 40 km, as well as Tatar (from the mainland) and Nevel. The latter freezes in winter and has a width of no more than 8 km.

Islands of New Zealand

The islands of New Zealand have a mainland origin. The arc on which they are located is located from the entire length of Australia. There are many faults in New Zealand, accompanied by volcanic eruptions and earthquakes.

After reviewing the information in the article, everyone will be able to correctly answer which islands are mainland.

As you know, the earth's crust is a very mobile and active substance. Of course, changes in the Earth's topography do not occur daily, but on a planetary scale, this system is very changeable. As a result of the constant shifts of tectonic plates, science has become aware of such a phenomenon as a mainland island. This is a certain territory, which now has an independent status from a geological point of view, but previously it did not have such.

Interpretation of the term

A mainland island is a piece of land that was once part of the mainland. This happened because at some point a certain piece of land sank below the level of the oceans, its most of remained in the same position, and the smaller one was completely separated by water. The result was an island, the structure of which is completely identical to the structure of the nearby mainland, but at the same time it is isolated from it by water. It is worth noting that in some cases islands of mainland origin do not have so-called parents. In other words, the continents from which they originated have long been wiped off the face of the Earth by global cataclysms.

Features of such a relief

Since the mainland islands arise by separating a small part of the earth from a large plot, the so-called offspring largely inherits the features of its "parent". Their geological structure, underground fossils and many other components are identical with the parent continent. However, it is important to remember that the separation of the island from the land is a process that can take centuries, therefore, the newly formed lands can have their own, unique features. Most often, the differences lie in the climate and everything that depends on it. The weather changes - new species of plants, animals and insects appear. If the island moves away from the mainland towards the equator, the flora and fauna become much more diverse. If the mainland island is directed away from the equator, its animal and vegetable worlds become scarce.

Well, now we propose to consider the features of the formation of such geological rocks and their varieties. Below is a list of mainland islands and the structure of each of them.

Orogenic subgroup

This is a unique natural phenomenon, which, however, is very common on the planet. It consists in the fact that the mountain ranges, as it were, go into the ground, and at a distance of several kilometers from the continent they again protrude from the water. Thus, the islands are born, which we refer to the group of orogenic. by the most a prime example given geological feature can be considered about Sakhalin is literally a continuation of the Ural Mountains. Novaya Zemlya, New Zealand and Tasmania also belong to the orogenic category.

platform islands

This type of island is a continuation of the daughter continent. It is completely identical to its mother earth both in terms of climate and in all other components. Such islands were formed due to bays and straits due to rising water levels in the oceans. In other words, any platform continental island is a shoal, which is located at a short distance from the coast. As good examples can be considered british archipelago, Canadian or Severnaya Zemlya. It is important to note that such islands are relatively young.

Continental slope island group

This category differs from the previous one in that the islands were formed by splitting tectonic plate and the separation of a small piece of land from the mainland. Such processes took place a very long time ago, therefore, these geological rocks have a very impressive age. It is also worth mentioning that a mainland island of this type is always separated from its daughter continent by an ocean strait and can be located at a very large distance. Madagascar is an excellent example of this category.

island arcs

The most seismically active parts of our planet are archipelagos, which have an arc structure. They are communities of small islands, sometimes so tiny that one house can barely fit on them. Such "peas" are grouped into vast archipelagos, which are located mainly at the junctions of the earth's crust. As a matter of fact, it was thanks to these joints that these archipelagos were formed. Therefore, such lands are subject to constant earthquakes, tornadoes, tsunamis and other unpleasant events can easily fall on them. natural phenomena. But oddly enough, we all love to relax in such places. This is the famous Philippine archipelago with thousands of islets in Indian Ocean, Caribbean and Japan.

Endemic flora and fauna

In this case we will talk not about clinical deviations in the health of people and animals, but about the formation of new, previously unknown species of fauna and flora. As you already understood, the separation of the island from the land is an incredibly long process, covering more than one human life. For such a long period on the lands that leave their mother's womb, the climate changes, and with it the entire biomass is transformed. It is important to understand here that not only the air temperature changes, but also the humidity - its level rises significantly. Therefore, mainly, the flora becomes denser and more diverse. As for the fauna, there is a paradox going on here. Mammals are getting smaller, weaker, and their overall numbers are declining. But reptiles, on the contrary, grow to abnormal sizes and multiply at an enviable rate.

We have considered all the features of this type of relief. Now we propose to take a look at examples of mainland islands. Perhaps you have ever been to one of them.

Tasmania and New Zealand

Despite the fact that both islands are located in close proximity to Australia, they have fundamentally different origins. New Zealand and all the small islands that surround it are on a tectonic arc. This is a seismically unstable area, where earthquakes and volcanoes erupt constantly. But Tasmania is a mainland island formed due to non-standard behavior mountain range. This is a continuation of the East Australian Mountains, which is separated from Australia by the Bass Strait.

Sakhalin and Japan

It is also a continuation of the mountain range, which is located at a short distance from the Asian part of our country. Sakhalin is characterized by a special flora, fauna and unique landscape. And here Japanese archipelago, which is located in close proximity to Sakhalin, are islands located at the site of a split in the tectonic plate. All of us, of course, have heard about the eternal natural disasters that cover the Land of the Rising Sun headlong.

The islands are divided into two large groups: continental and oceanic.

mainland islands- these are sections of the mainland that separated from it (i.e., became islands) due to the flooding of parts of the mainland by the sea that experienced splits or subsidence under the influence of tectonic forces. In most cases, the separation is purely external, reflected in the fact that the surface of the island and the surface of the mainland are separated by a water surface, and do not merge into one another without interruption. In fact, by their foundations, the continental islands continue to be connected with the body of the continent, since these foundations rest either on the continental shelf (Novaya Zemlya, Wrangel Island, Newfoundland, Great Britain with Ireland, Tasmania, etc.), or on the continental slope (Madagascar , Ceylon, Sardinia, Corsica, etc.).

Oceanic islands have nothing to do with the continent, that is, they have never been part of it and arose completely independently of the continents. According to the method of occurrence, oceanic islands are volcanic and coral.

Start volcanic island gives a volcanic eruption at the bottom of the sea. In shallow places, an island may appear in one go, but those islands that are now rising from great depths, appeared on the day surface, probably as a result of repeated eruptions and successive accumulation of volcanic products. The growth of the island continues after its appearance above sea level, and volcanic islands are almost always of considerable height. In this respect, Fr. Hawaii, consisting of five merged volcanoes, of which Mauna Loa and Kilauea are still active. Mauna Loa is submerged by its base to a depth of 4600 m, and its height above the sea is 4166 m; thus, this gigantic volcanic structure rises 8766 m above the seabed, that is, almost to the height of Everest.

Volcanic islands scattered throughout the oceans under the most diverse latitudes. In the Mediterranean Sea, the most famous are the Aeolian Islands, Pantelleria, Santorini, Atlantic Ocean- Jan Mayen, Azores, Madeira, Ascension, St. Helena, Gough, Tristan da Cunha, Bouvet, etc. There are fewer of them in the Indian Ocean (Crozet, Kerguelen, Amsterdam, etc.).

The Pacific Ocean is especially rich in volcanic islands. Here they are located both in the center (many islands of Oceania, Hawaiian, etc.) and along the outskirts (Galapagos, Juan Fernandez, a number of small Sunda, Easter Island, etc.).

Coral islands are one of the varieties of buildings erected by corals - marine colonial organisms with a calcareous skeleton. Calcareous algae, foraminifers, pelecypods, gastropods, etc. also participate in the construction of coral structures. The structure grows due to the fact that new animals settle on the skeletons of dead animals, which in turn are replaced by other generations. The growth of one meter of polyp forest requires, depending on the conditions of the coral habitat, from 35 to 335 years.

Corals are very demanding on habitat conditions, and therefore the geographical distribution of coral structures is strictly limited. Reef-building corals can exist only in warm (with a temperature of at least 18 °) waters, as a result, neither in polar nor in temperate latitudes coral formations do not arise unless these temperate latitudes are heated by warm sea currents, such as, Bermuda(the existence of these coral islands associated with the Gulf Stream). Due to the high demand for heat and light, coral colonies at depths exceeding 40-60 m also do not live, because there is not enough heat and light. In addition, normal or high salinity is necessary for the favorable development of corals. sea water and adequate oxygen saturation. There are no coral colonies against the mouths of the rivers, because the river brings fresh water. They are also absent in such stagnant bays, the shores of which are covered with mangroves, for there is not enough oxygen; for the same reason, any coral structure grows more vigorously on the side facing the ocean than on the opposite side: on the ocean side, the water, set in motion by waves and surf, is continuously mixed with air and is better saturated with oxygen.

Corals, as marine organisms, can only build their structures to the level of the ocean. Coral structures rise above the water only a few meters, and this is due largely to the heaping of fragments of coral limestone by the action of the surf. On the other hand, the thickness of a coral structure cannot exceed 40-60 m, i.e., the greatest depth of coral habitat. However, in a number of cases, structures were observed that rose excessively high above the water, as well as their thickness, significantly exceeding 60 m (over 300 m in the Funafuti Atoll in the Ellis Islands group). A satisfactory explanation of these cases can only be found on the assumption that either the seabed, on which the base of the coral structure lies, was subjected to uplifts and subsidence, or the ocean level slowly rose and fell.

If the level of the ocean does not change, but oscillations of the bottom occur, then with a slow sinking of the bottom, the coral structure, continuing to grow upwards, will continuously increase its thickness; the maximum possible value of this power is determined by greatest depth reached by lowering the bottom. It is important that this sinking proceed slowly enough - no faster than the growth of coral upwards; rapid sinking will cause the death of corals, as it will take them to a depth that is not favorable for their existence. When the seabed rises, the coral structure is pushed above sea level; however, its further natural growth upwards is stopped due to drying.

A similar result will be obtained under the condition of the immobility of the seabed, but with fluctuations in the level of the ocean. Here, the rise of the level in its consequences is equivalent to the lowering of the bottom in the first example, and the lowering of the level is equivalent to the rise of the bottom.

Eustatic fluctuations in the level of the ocean (that is, fluctuations covering the entire World Ocean) are quite possible and have been proven in a number of cases. But the assumption of the rise and fall of the seabed seems more convincing, since the fluctuations of the solid earth's crust are a universal and indisputable phenomenon for all periods of the existence of our planet.

Coral islands in their distribution are very often associated with volcanic structures (both those that appeared on the daytime surface, and a little undergrown to it). Without this, the existence of coral islands in open ocean, in the area of distribution of great depths. First, a volcanic cone grows from the bottom of the sea; when its top is so close to the level of the ocean that the depth of the sea in this place becomes favorable for the settlement of corals, colonies of coral polyps begin to develop.

There are three main types of coral structures: coastal reefs, barrier reefs and atolls (lagoon islands). Coastal, or fringing, reefs are closely adjacent to the coast of the mainland or island. barrier reef separated from the land by a more or less wide strip of water. An atoll is an island in the form of a ring, closing on all sides the inner calm lagoon; at the same time, the slopes of the atoll descend steeply (up to 45 °) to the ocean, in places sheer (for example, part of the slopes of Bikini Atoll in Marshall Islands), and inside the lagoon is gently sloping.

Coral structures are usually broken. Coastal reefs off New Guinea Solomon Islands, in the New Hebrides are absent in places where fresh water is brought from land, as well as in areas abounding in mangroves. The same must be said about the barrier reefs that exist around almost all the Pacific islands. volcanic origin, - in Tahiti, Fiji, etc.; there are especially many of them in the Coral Sea. Broken in many places and the Great Barrier Reef, stretching for 1900 km along the Australian mainland from Cape Sandy to the Torres Strait; the inner channel separating the barrier from the mainland is not deep (35-70 m), but its width varies from 35 to 125 km.

There is usually one or more gaps in the atoll ring. The inner lagoon is shallow - no more than 100 m (in Tuamotu, for example, the depth is not more than 25-35 m), and the water in it is exceptionally warm; Thus, Agassiz on Funafuti (in the Ellis Archipelago) at a depth of 27 m found a temperature of + 31 °. Some of the lagoons are really small. inland seas; individual lagoons on the Tuamotu have a length of up to 55-70 km, and in the northern part Maldives up to 140 km (with a width of 30 km). At the same time, the average width of the ring bordering the lagoon usually does not exceed 0.5 km.

There are coral islands in the Atlantic Ocean (Bahamas, Bermuda), in the Red Sea, Indian Ocean (Maldives, Laccadives, Chagos Archipelago), but the classic area of their development is the Pacific Ocean. North and east of coral sea atolls are becoming more and more numerous and in some archipelagos they are already the only type of coral buildings. The most numerous atolls are in the Gilbert, Ellis, Tuamotu archipelagos and on the Marshall and Caroline Islands. Tuamotu has about 70 atolls of regular (round or elliptical) shape; their inland lagoons are themselves often dotted with coral islands.

Of particular interest are the "imperfect atolls", that is, those in which, among the lagoons, islands not of coral, but composed of igneous rocks, protrude. An example is Mangareva (Tuamotu group), Fr. Hermite (west of the Admiralty Islands), in whose lagoon there are four volcanic islets, as well as Truk Lagoon (in the center of the Caroline Group); in the Truk lagoon, with a diameter of about 60 km, there are at least 16 islands resembling mountain peaks, and one of them reaches a height of 480 m above the sea.

coral islands in pacific ocean located on underwater hills, elongated, as a rule, from the northwest to the southeast (the islands of Caroline, Marshall, Marquesas, Tuamotu, Samoa, Tubuai, etc.).