Continental movement. How are volcanic islands formed? Freshwater islands

1. Isolation and remoteness from the mainland determine the high endemism of flora and fauna. How ancient island, the more endemic types and forms. For example, species endemism of the flora of New Zealand, New Caledonia, Hawaiian Islands reaches 70-80%. At a lesser distance from the mainland (the islands of Great Britain, Ireland, Japan, Sri Lanka), endemism is less pronounced.

2. On the islands, often in the guise of certain groups of animals, deviations. For example, large mammals are usually smaller than on the mainland (ponies, Philippine buffalo, etc.). In birds and reptiles, on the contrary, island gigantism is expressed (lizards on Komodo Island, turtles on the Galapagos Islands). The reason for this phenomenon has not yet been elucidated.

3. Often the islands are characterized flightless birds and insects. The origin of flightless birds is associated with absence on islands mammals that could exterminate them. They played an important role in the selection of flightless insects. wind drift and hurricanes into the ocean. For many species of flying insects, an equilibrium is established between the number of individuals blown away by the wind and the number of individuals brought to the island, provided that the island is part of an archipelago.

4. In your distribution biocenoses of the islands obey the same zonal patterns as the communities of the continents. However, their structure and energy connections with a smaller species composition easier. Only on large islands with mountain systems (Madagascar, New Zealand, Cuba, Great Britain, etc.) the vegetation cover and animal population are no less complex than on adjacent continents. On islands with a simplified landscape characteristic, the communities are more uniform, and the depletion of the species composition is more significant.

3. Biomes of oceanic islands. On islands of oceanic origin, communities arise on the products of volcanic activity or coral limestones. The flora and fauna of these islands is entirely immigrant, but may be older than the islands themselves.

Features of the biota of oceanic islands

1. Species penetration from the mainland to one or another island is facilitated by the so-called " land bridges» and along a chain of islands of volcanic or other origin. On some of these islands, the species may have had a temporary home and migrated to the newly formed island as a relic that arose as a result of extinction in neighboring land areas. Thus, the possibility of an element of relict origin of flora and fauna on the islands of oceanic origin is not excluded.

2. Transfer of organisms through body of water in relation to each individual is random character. With the long existence of the migration process, this transfer acquires a certain statistical probability. So, when crossing a space 100 miles wide, only one individual out of a thousand survives, the next 100 miles - again one individual out of a thousand, and so on. The chance of reaching an island located 200 miles from the source of migration is one in a million.

3. The most common ways of colonizing the islands by organisms are hydrochoria(sea currents), anemochory(winds, storms and hurricanes) and zoochory(transfer by birds). In the colonization of the islands by plants and animals, man plays an important role (anthropochory).

4. Actively populate the islands can mostly birds, however, this process is constrained by the "nesting conservatism" of the birds themselves. Mature plants washed ashore by waves, as a rule, rarely take root. Epiphytes that are on the trunks survive. carried by the wind over long distances spores and light seeds, in connection with which, for example, ferns on the islands are widespread. Insects generally do not tolerate salt water well and colonize the islands if they are carried by wind or birds. Dying in sea water amphibians, reptiles and freshwater fish. Of the reptiles on the islands, only geckos and skinks. Ultimately, death in sea water leads to a rather poor species composition of these groups of animals. So, in South America there are many amphibians, and on the neighboring Galapagos there are neither frogs nor salamanders, there are no bird species characteristic of the mainland, and from land mammals one genus of bats, rats and a rodent resembling a hamster are represented.

5. Of great importance in the settlement of the island by organisms carried by the wind and, to a lesser extent, water, is its "hunting corner"- the location of the island in relation to the flow of migrants. So, if the island is located perpendicular to the flow of migrants, then the probability that the migrant will end up on the island is greater.

The flora of the islands of oceanic origin is characterized by a small number of species composition. Their fauna lacks mammals, amphibians and snakes.

6. Speciation process flows on oceanic islands faster, than on the mainland and continents, since on oceanic islands, as a rule, a small population of any species with a depleted gene pool is formed. In addition, this local small population is in geographical isolation. As a result, on different islands, differences arise in the set of genes of the same species, leading to the emergence of intraspecific forms on each island, and subsequently species. In this case, the unfilled ecological niches are also of great importance.

As evidence that reliably confirms the originality of speciation on islands of oceanic origin, one can cite finches living in the Galapagos.

Ch. Darwin in his diary, A Naturalist's Journey Around the World on the Beagle, noted that natural history of these islands is highly interesting and well worthy of attention. Most of the organisms living here are natives, not found elsewhere. This "satellite of America", separated from the mainland by an open ocean of 500 - 600 miles, received several random colonists from the continent. Obviously, one species of finch, feeding on its own food, got to the Galapagos. Finches that did not have enough food died or switched to other food. So, they learned to catch insects, pull out larvae from cracks in tree trunks, crack nuts, eat plant leaves, etc. Ultimately, natural selection led to the formation of specialized forms that filled all the ecological niches on the island intended for songbirds. In the Galapagos, there are 3 genera, 13 species and 37 island forms of finches: large, medium and small ground finches, cactus, thick-billed arboreal, woodpecker, parrot, coconut, mangrove, warbler, etc. Interestingly, the Darwin woodpecker finch, which does not have a long tongue, uses a cactus needle to get an insect from under the bark of a tree.

Quite exotic representatives of the endemic fauna also live on the Galapagos Islands: giant tortoises, ancient marine and terrestrial iguanas, sea lions, lava snakes, flightless cormorants and the Galapagos penguin. Most representatives of the biota of the islands have relatives on the South American continent.

7. A characteristic feature of the biota of the islands is constant delivery» settlers. Species that arrived on the island earlier have an undeniable advantage over ecologically close species that arrived on the island later. The first settlers have more time to reproduce and increase in numbers in the absence of competition or the presence of weaker competition.

8 . Each species can naturalize on the island only under the following conditions: three conditions:

– successful n the birth of ecesis (a full development cycle from the appearance on the island to the bringing of viable offspring, inclusive);

– survival in competition with species that previously inhabited the island;

– adaptation to new conditions of existence.

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. Eg, British Isles 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, Sakhalin Island is a continuation of the Far Eastern mountain 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. In terms of total area, the islands created by volcanoes are 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 volcanic origin the island of Sicily, 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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Oceania - this is the name of the largest cluster of large and small islands on our planet in the western and central part 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. Most major islands Polynesia is New Zealand, Hawaiian Islands, Tonga, Samoa, Wallis, Tokelau, Horn, Cook, Tuvalu, Tubuai, Societies, 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 Marshallese, Caroline and Mariana Islands and 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, coral reefs and entire islands appear above the surface of the water, and if coral deposits occurred along the contour of the vent 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 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.

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

There are three types of islands: mainland, volcanic and coral. The formation of islands took place not only many thousands of years ago, but even now new island territories are emerging.

How were the mainland islands formed?

The mainland islands were formed due to the movement tectonic plates earth's crust. Once the islands were part of large continents. The vertical movements of tectonic plates, together with the rise in the level of the world's oceans, formed faults in the continents. The nature of the mainland islands and the nature of the mainland closest to them are almost identical. Continental or continental islands are located within a single shelf, or are separated from the mainland by a deep fault. The continental islands include Greenland, new earth, Madagascar, British Isles, etc.

How are they formed volcanic islands?

Volcanic activity is constantly taking place in the oceans. An erupting volcano emits a huge amount of lava, which, solidifying on contact with water and air, forms new volcanic islands. Such islands experience great water erosion and gradually go under water. Volcanic islands are often far removed from the mainland and form a unique ecological system. An example of volcanic islands is the chain of Hawaiian Islands.

How are coral islands formed?

Such islands can form only in equatorial and tropical latitudes. The shoals are inhabited by corals and polyps, which hook on to the seabed with their roots. Over time, the bottom of the coral hardens, forming a solid foundation for the island. Such a base begins to retain the sand that the ocean carries with its course. Coral reefs are formed, which are inhabited by the most outlandish animals of the ocean. An excellent example of such islands is the Big barrier reef off the coast of Australia.

Continents and oceans do not always occupy the same position on Earth. Although we do not notice it, they are constantly moving at a speed of only a few centimeters per year. Surface movements served as the basis for the creation of the theory of plate tectonics. The solid outer layer of the Earth, called , varies in thickness from a few to 240 km and is divided into six main plates. The heat of the deep inner layers of the Earth allows the plates to move on top of the hot molten inner layer (asthenosphere). The outer part of the lithosphere is called the earth's crust.

The oceanic crust that forms the bottom of the oceans is made up of basalt. The continental crust consists of granite, which has a lower density than basalt, and therefore it remains at the top. Oceans form, grow, shrink or disappear as the plates move. Eg, Atlantic Ocean has expanded by about 15 meters in the last 500 years.

Modern continents are similar to those that existed 400 million years ago, when, after a series of collisions, individual continents merged into the only huge supercontinent Pangea. About 160 million years ago, huge thermal vertical flows from the inner layers of the mantle stretched the earth's crust, and Pangea split into two large parts: Gondwana in the south and Lauraeia in the north. Gondwana consisted of modern South America, Africa, India, Australia and possibly Antarctica. Lauraeia was made up of the current North America, Europe and Asia. They were separated by the Tethys Ocean. About 100 million years ago, when the African and South American plates began to diverge and Laurasia split in two, the Atlantic Ocean began to form. About 80 million years ago, India separated and moved north, closing the Tethys Ocean. The Gondwana rasol ended about 40 million years ago, when Australia separated from Antarctica. Even today, the coastlines of the continents, formed in the places of faults, surprisingly exactly coincide. The plates are still moving. North America is moving away from Europe at a rate of about 8 centimeters per year.

Ocean floor formation

Where the two plates moved apart, hot matter from the deep layers of the mantle rose, filling the space and forming a new ocean floor. Ocean ridges have formed along the fault lines. The Pacific and Nazca plates, which make up the bottom, were moving apart faster than all the others, at a rate of about 14 cm per year. Where two plates collided, one went under the other and plunged into the mantle. Such a place is called a fault zone, where ocean trenches arose. Usually in these places there is increased seismic activity, the probability of earthquakes is high. Earthquakes are also common where two plates are pressed into one another, as happened at the San Andreas Trench near west coast North America.

The birth of the ocean

Someday the Red Sea may become an ocean. The African and Arabian plates began to move apart 70 million years ago and continue to move apart at a rate of 0.5 cm per year. Probably due to this displacement, the East African Rift Zone, a crack in the continental crust that stretches from the Jordan Valley and Dead Sea north through East Africa South. When the break reaches coastline, it will connect the Red Sea with the Mediterranean. This connection was broken and restored several times. The Red Sea was once naturally connected to mediterranean sea and the Indian Ocean.

death of the ocean

The Tethys Ocean was squeezed by two plates when the Indian plate collided with the Eurasian plate and shifted under it. When the mainland crust of India collided with the crust of Asia, it warped and the Himalayas formed. Part of the shallow continental shelf of the Tethys Ocean was uplifted in this process, so that sea shells are now found in the Himalayas, at an altitude of several thousand meters.

How are islands formed?

Some islands are formed from fragments of the granitic earth's crust, torn off the continents and remaining in the same place. So, for example, the Seychelles were part of or in "hot spots". "Hot spots" are places where magma flows rise to the surface from the earth's mantle. The "hot spots" are stationary, and the chain forms as the plate moves over them. There are 16 "hot spots" known, including the Hawaiian archipelago and the Partnership Islands. Midway is the oldest of the Hawaiian Islands and the furthest from the hotspot.

Volcanic oceanic islands often turn into atolls if they are located in areas of warm climate. At first, the island is surrounded by a coral reef, and as the island sinks, the reef continues to grow. In the end, the central island may disappear, and in its place remains a lagoon surrounded by a coral reef.

Tidal waves are almost unrelated to tides. Usually they are caused by underwater volcanic eruptions, or earthquakes, which create the movement of water masses and high waves. Pillow-shaped lava is formed when a volcanic eruption occurs beneath. As the water cools the lava rapidly, it takes on a strange rounded shape. Islands often have unique plant and animal species. On islands of mainland origin, there are species that may be descendants of those that existed on the mainland thousands of years ago, such as the sea coconut on Seychelles. Other animal and plant species reach oceanic islands due to wind, ocean currents and floating objects such as logs, or they are transported by people.