Island Pokonji Dol in Croatia in the Adriatic Sea.

The island's birthplace in France on the Seine in Samois-sur-Seine.

An island or island ^Definition

Here is the definition of islands that give the United Nations Convention on the Law of the Sea , 1982: "An island is a naturally formed area of land surrounded by water that remains at high tide" which reproduced the definition that in giving, in its article 10 the Convention on the Territorial Sea and Contiguous Zone , signed at Geneva in 1958. If there is a line between an island of a continent , generally, it is set to Australia. But the question of whether Australia is one or the other remains open.

A small island is an island. Infrieuere limit the size of an island is, as opposed to a rock , it is suitable for human habitation or economic life of their own .

Several islands close to each other form an archipelago.

A peninsula is connected to a tract of land by a much broader isthmus.

Some islands and peninsulas are accessible at low tide and then lose their insular. Again, it is possible to consider or not as full-fledged islands.

Etymology

Its etymology Latin , insula, gave the word "island" also called "islander." Au pluriel, le terme les dsigne couramment les les des mers chaudes comme les Antilles ou des archipels d' Ocanie. By extension, the noun "island" means someone or something from the Caribbean, although the use of this term has no geographical consistency.

Place names can keep track of an ancient island, such as Lille in France , or by analogy, as the French region of Ile-de-France , extension of the former royal domain of the Capetian , which is not a island, whose inhabitants are called "Parisians".

Training

By the rising waters

The continental islands are so named because they are located on the same shelf as the continent that is close to them. It is therefore actually a part of the continent: it is the height of sea level which makes it is an island (in the case of Britain at that the last glaciation was no longer an island). Some islands also are not only tide high (the Mont Saint-Michel or the Island of Noirmoutier , for example). In these cases, the depth of the sea around them is (relatively) low. (See related article Island accessible at low tide .)

The continental drift

The Australian was, there are hundreds of millions of years, attached to the Antarctic. Madagascar was attached to Africa. In both cases, a tectonic plate has ruptured to give two have diverged gradually over the earth's surface at a speed of several centimeters per year (1 cm per year for 100 million years = 1 000 km). It is also the case of Corsica and Sardinia , which were attached to the European continent, there are more than 30 million years. ^{By volcanic accretion}

Here are the lava accumulated one or more volcanoes that emerge through the accumulation of volcanic products , forming the island. The depth of the sea around may be very large (several thousand meters). The examples in the middle of the ocean are not geologically from any continent.

The islands volcanic arc subduction

A type of volcanic island is located on an arc of volcanic islands. These islands arise during the subduction of one plate under another. Examples are the Mariana Islands , the Aleutian Islands and most of Tonga in the Pacific Ocean. Some of the Lesser Antilles and South Sandwich Islands are the only examples in the Atlantic Ocean.

Volcano rift and oceanic ridge

Another type of volcanic island emerges when oceanic rift reaches the surface. There are two examples: the Iceland , which is the largest volcanic island in the world and Jan Mayen , both in the Atlantic. The birth of the island of Surtsey in 1963. In the Mediterranean we can see the island of Pantelleria.

The islands of Hawaii are hot spot volcanoes.

Wake Island was a volcano hot spot before becoming an atoll coral.

The islands of the hot spot.

The last type of volcanic island formed at the hotspot volcanoes. A hotspot is more or less stationary relative to the moving tectonic plate above it. A chain of islands emerges when the plate moves. Over long periods, this type of island is eventually eroded and submerged by the isostatic adjustment to becoming a seamount. The movement of the plates at a hot spot produces a line of islands oriented in the direction of motion of the plate. For example, Hawaii , from Hawaii to the Atoll Kure , then extending beneath the surface of the ocean, take a northerly direction at the Seamount of the Emperor. The island of Tristan da Cunha is an example of a volcanic hotspot in the Atlantic Ocean.

By accretion

Islands coral

An atoll is an island formed from a coral reef that was built on an eroded and submerged volcanic island. By the accumulation of coral polyps and several hundred meters in height, the reef emerges from the water surface and form a new island. The atolls are often in the form of a ring with a lagoon and shallow center. Examples are the Maldives in the Indian Ocean and Rangiroa in the Pacific.

River Islands

The river islands appear in the river deltas and in large rivers. They are formed by deposition of sediments at points where the current loses some of its intensity. By nature, they are parts of the river current isolated. Some are ephemeral and can disappear when the water volume or velocity of the stream change while others are stable and durable.

By accretionary tectonics

The islands west of Sumatra are accretionary prism emerges. If movements continue these islands will grow and increase the area of Sumatra.

At subduction zones where two tectonic plates converge reverse faults and folds are formed which thickens the crust, and traced the bottom of the sea As the island of Barbados in the Caribbean , is a prism accretion emerges. It's the same thing for the islands west of Sumatra : Simeulue , Nias .... For the island of Nias , the earthquake of 28 March 2005 raised a portion of the island, increasing still further its surface.

The rise of the lithosphere

At the Baltic Sea and the fjords , cast iron, 10 000 years ago, a glacier that covered it, gave up the lithosphere (isostatic rebound) bringing out new lands and islands as Bornholm.

Geography

Insularity

The definition of the island as an area of land surrounded by water leads to congregate in the same category of land very different from the island to the mainland, where the degree of insularity is highly variable. This degree of insularity is difficult to define and assessed differently depending on whether one looks at the geography physical or human, with the economy and transport , or biology or the ecology.

In terms of physical geography , an author, Francis Doumenge , defined measurable criteria for assessing the degree of insularity:

• the "coastal index", defined as the ratio between the length of the ribs and the surface of the island. This index is maximum, two or more, in the case of atolls, where the presence of a central lagoon substantially increases the length of the coastline. According to the relief (or very massive cut) and the general shape of the island (more or less circular or elongated) index varies greatly. He considers that below 1 / 25 (one km of coastline for 25 km ^2), the island has a strongly continental.
• the "isolation index" defined as the ratio between the surface of the Exclusive Economic Zone (EEZ) of 200 nautical miles and that of the island. In the case of Clipperton (2 km ^2), with no land mass in the radius of 360 km, this index is very high. It decreases when the islands are closer. Below 1 / 100, we can no longer speak of insular isolation.

This author also defines an "index of endemism "which is the ratio of the total number of taxa (genera, species and subspecies) of the island population by the number of endemic taxa. This index gives an idea of the importance of endemic plant and animal , that is to say the biological isolation, which characterizes a given island.

The index of isolation of the United Nations Program for Environment (UNEP, 1998), is more complex. It consists of adding the square root of the distance from the island of equal size or greater than the nearest square root of the distance from the nearest archipelago and the square root of the distance from the nearest continental country. This index is highest (149) for Easter Island. It is 102 to Tahiti and 23 for Corsica.

These indexes do not account for human activities, the importance of population and the accessibility (eg presence of an international airport).

One can also question the relevance of the island as an object specific geographical. One researcher, Franois Taglioni , conducted a study on small island spaces in the world to revisit the concepts that affect the islands and territorial dynamics that this category of spaces with one another.

Size

If we assume that Australia is a continent, the two largest islands are Greenland (also larger island of North America ) and New Guinea (the largest island of Asia ).

Madagascar is the largest island of Africa ^(4th world), the UK is the largest of Europe ^(9th in the world) and in Oceania , is the largest island in the South Island , in New Zealand ^(12th in the world), the largest island of South America is the Great Island of Tierra del Fuego ^(29th in the world) that of Antarctica is the Alexander ^I. Island (30 ^th the world).

Ecology

The study of islands has influenced Charles Darwin and many ecologists and founded theories of landscape ecology , including that of the ecological insularisation.

Ecology islands

The islands can accommodate true that some species when they are small, but from a threshold size are important factors of biodiversity , including the endemic and shelter they can afford.

In an ecological network , they can serve as a "ford" for species that can fly or have good colonizing abilities on the water or air. Species that live there are often smaller (dwarf elephants lived eg Corsica and Sardinia until the islands were colonized by humans).

For example, in the broad biogeographic realm that is the Mediterranean basin (three million km ² ), the islands and islets are only 4% (103 000 km ²⁾ land area of approximately , with 4000 islands of less than 10 km ² and 162 islands and over 10 km ^2, distributed in a manner not consistent, particularly where biodiversity has declined but still constitute a remarkable reservoir.

The concept of the island is also used metaphorically to describe any "isolate biogeographic "in which populations of living beings are isolated, forming islands in the biological sense. When will that process is underway in the context of ecological fragmentation , we speak of " ecological insularisation.

An international partnership has been initiated to help the islands to share and be heard on the environment, as part of the Global Convention on Biodiversity (Rio, June 1991), says "Global Island Partnership (or GLISPA) .

Vulnerability

Ecological systems or islands insularisation (true or made islands in the sense of landscape ecology) are often simplified and endemism factor, and therefore more vulnerable to disturbance, particularly man . Especially species introductions (intentional or unintentional) are often due to biological invasion seriously disrupting the ecological balance Island which led to the extinction of many species in recent centuries. Hner Greuter and showed in 1988 that these invasions do not affect the islands, but also the larger islands Madagascar , New Zealand or Australia.

In History

Colonization human

Some islands were uninhabited when discovered by the Europeans. This is the case of Madeira , the Azores , the island of Mauritius , the Reunion , the Seychelles , of St. Helena ... Others were inhabited, but their first occupants were exterminated by the colonists: the case the Guanches in the Canary Islands , the Caribs in the Caribbean or Jamaica , the Ona Indians of Tierra del Fuego , the Aborigines in Tasmania.

Utility for isolation

Isolation, a term whose etymology is related to "island" through the Italian insulation, and loneliness are often sought in the islands, whether voluntary or not:

• voluntary isolation:
  • Paul Gauguin , the Marquesas Islands ,
  • Jacques Brel , the Marquesas
  • Robert Louis Stevenson , the Marquesas Islands and then to Samoa.
• forced confinement:
  • Robinson Crusoe ,
  • The mutineers of the Bounty ,
  • Napoleon was under house arrest on the island of Elba and then to St. Helena ,
  • the Marshal Petain was imprisoned on the island of Yeu ,
  • the Dreyfus and Papillon in the Devil's Island ,
  • Nelson Mandela at Robben Island near Cape Town.

Prisons have been installed in the islands to limit the possibilities of escape :

• Alcatraz in the bay of San Francisco ,
• the French Guiana penal colony in the islands Hi ,
• the prison at Noumea in the Nou Island ( New Caledonia )
• the prison island of R ,
• the galleys of Poulo Condor ( Vietnam )
• a penal colony on Staten Island ( Argentina )
• a concentration camp on Dawson Island ( Chile ).

In literature

Here are some examples:

• the late 8th century BC: The Odyssey of Homer
• 1719: Robinson Crusoe by Daniel Defoe
• 1844: The Count of Monte Cristo by Alexandre Dumas
• 1874: The Mysterious Island by Jules Verne (see also The School of Robinsons and two years of holidays )
• 1883: Treasure Island (Treasure Island) Robert Louis Stevenson
• 1954: Lord of the Flies (Lord of the Flies) by William Golding
• 1962: Island (Island) by Aldous Huxley
• 1962: Island of Robert Merle
• 1994: Island of the Day Before (L'isola del giorno prima) by Umberto Eco

References

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