Island

We explain what an island is, what types exist, their characteristics and how they are formed. Also, what are plastic islands.

What is an island?

an island It is a portion of land that is naturally surrounded by water, and that is smaller in area than a continent but bigger than an islet. Islands are very common in world geography, and have different shapes, topography, and geological origins. When several of them are found together in the same region of the ocean, they are known as an archipelago.

The separation of islands from the mainland usually influences the life that develops on them, giving rise to endemic species that have evolved in isolation and independently of their continental counterparts. For many centuries, maritime exploration by humanity consisted of searching for secret and mysterious islands.

In fact, islands have been very present in the imagination of humanity since ancient times. Entire countries consist of one or more politically grouped islands, and many of them were formerly used as prison destinations or as initiation places in which to test the tribe's warriors, who had to survive on their own.

In this way, the islands gained a prominent symbolic value in myths and literary stories of all times, generally as an unprecedented place, where treasures and wonders can be found, but they can also be abandoned and isolated, as in the shipwrecked stories. In Ancient Greek texts, the islands were often populated by deities and mythological beings, such as the sorceress Circe or the daughter of the titan Atlas, Calypso.

See also: Physical geography

Characteristics of the islands

In a general sense, the islands are characterized by the following:

• consist of a portion of land surrounded by water on all its sides. This may mean that it is in the middle of the ocean, a river, or a lake or lagoon.
• According to international standards of the Millennium Ecosystem Assessment must exceed 0.15 km² of surface and be separated from a continent by at least 2 km of water. However, they otherwise have very diverse topography, climate and geography, but
• Very small islands are known as islets and they are rarely populated. However, when many islands are put together, they are referred to as an archipelago.
• The largest island in the world is Greenland with 2,175,000 km² total surface area, and is located in the North Atlantic Ocean.

Formation of the islands

Islands are formed as a consequence of different geological processes. Some are due to volcanic and/or sedimentary activity which slowly accumulates materials until they harden and form a solid territorial platform.

Therefore, in theory, it is not impossible to witness the appearance of new islands after important tectonic movements or large underwater volcanic eruptions. However, these processes usually take place over very long periods of time.

Other islands are due to historical changes in ocean water level given that the sea has not always been at the same level as we see it today. The increase or decrease in water can cover or expose entire portions of the continental shelf, respectively, and thus create islands or, conversely, join them to the continent.

Types of islands

The classification of the islands responds precisely to the mechanisms that led to their appearance. So we can talk about:

continental islands. Those that are part of the continental shelf, and therefore have the same materials, the same textures and are located in the relative proximity of the coast, although separated from the main land by extensions of water that are not too deep (200 meters deep). depth or less). This occurs when the ocean water level rises and submerges portions of land, “creating” islands by separating them from the rest of the continent. Examples of this type of islands are:

• The Malvinas or Falklands Islands, in the South Atlantic off the Argentine coast.
• The island of Greenland, separated from North America by the Atlantic Ocean.
• The British Isles, territory of the United Kingdom, separated from Europe by the North Sea and the English Channel.

volcanic islands. Those that are formed due to the eruption of underwater volcanoes, which pour magma and liquid rock materials out of the subsoil, where they cool and solidify, settling until emerging from the water. They can be of three types: island arcs in subduction zones, mid-oceanic ridges and intraplate hot spots. Volcanic islands are the youngest islands in geological terms, and are not part of any continental shelf. Examples of them are:

• The Antilles, a group of islands in the Caribbean Sea.
• The islands of the Hawaii archipelago, in the Pacific Ocean.
• The Galapagos Islands, located in the Pacific off the Ecuadorian coast.

mixed islands. Those that are the result of the combination of volcanic and continental processes, that is, they combine both previous types. Examples of them are:

• The islands of the Aegean Sea, between Greece and Türkiye.
• The islands of Japanese territory.

coral islands. Those that form in tropical and subtropical seas due to the accumulation of biological waste from corals: primitive marine organisms, whose calcareous shells are capable of reaching large proportions. When deposited on shallow underwater platforms or volcanic cones, they produce recognizable islands. Such is the case of:

• The Maldives islands, about 1200 islands located in the Indian Ocean, 450 km from the Indian coast.
• The Los Roques archipelago, on the Venezuelan Caribbean coast.
• The Chagos Archipelago, in the Indian Ocean, 500 km south of the Maldives.

sedimentary islands. Those that occur due to the gradual accumulation of materials resulting from the flow of larger rivers, which carry gravel, mud or sand in large quantities. Where the current loses speed, these materials settle and an island begins to form, generally around the river delta. This occurs in cases of:

• The islands of the Orinoco delta, in eastern Venezuela.
• The islands of the Ganges River delta in India.
• The island of Marajó, at the mouth of the Amazon River, in Brazil, the largest in the world, with a size equivalent to Denmark.

river islands. Those that are formed from barriers in the central channel of a river, as its channel changes historically, exposing floodable coastal ridges and platforms, such as banks and swampy depressions. Such is the case of:

• Bananal Island, in Brazil, considered the largest river island on the planet.
• The “ait” of the River Thames, in England, like Eel Pie Island in Twickenham.

plastic islands

Plastic islands, garbage islands or toxic islands are a recent and painful phenomenon, which is not due to natural geological processes, but to the lifestyle of human beings in the last century of their existence.

These are gigantic agglomerations of floating garbage that has been dumped into the sea by human societies and that, due to the action of the elements, its particles are reduced to small sizes, close to that of a grain of rice. For the most part they are made of plastic and non-biodegradable materials.

These immense islands of garbage are formed due to the circulation of ocean water, which gradually accumulates floating microfragments in patches of variable extent. The largest of all varies between 710,000 and 17,000,000 km² surface larger than the territory of many countries, and is located in the heart of the Pacific Ocean.

The garbage contained in them is not only difficult to detect from the air and by means of radar, due to its small dimensions, but it is destroying the marine ecosystem little by little.

Since plastic does not biodegrade, when ingested by animals it causes their death, and also obstructs the flow of plant species, preventing them from accessing sunlight. The mere existence of this type of phenomenon should be a reason to stop the consumption and manufacture of plastics throughout the world.

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References

• “Island” in Wikipedia.
• “Garbage Island” on Wikipedia.
• “Island” in the Language Dictionary of the Royal Spanish Academy.
• “How are islands formed? What is an island?” (video) in Drawings.
• “What are garbage 'islands' in the oceans and how do they form?” in Environmental Forum.
• “Island” in The Encyclopaedia Britannica.