The islands They are landmasses emerged and stable, found in oceans, seas, lakes and rivers, surrounded by water on all sides. Being generally a relatively small land mass compared to a large body of water, they have particular characteristics.
Among these characteristics is the effect of the mass of water that surrounds the island on the climate, determining the direction of winds, rainfall, temperature and humidity. In addition, these geographical formations are formed by various processes, such as land elevation, volcanism, sedimentation or biological activity..
When these formation processes give rise to several islands very close to each other, the group is called an archipelago. On the other hand, there are different types of islands depending on their location and geological origin..
In such a way that by location there are continental, oceanic, lacustrine (lakes) and riparian (rivers) islands. While by geological origin there are volcanic, continental, coral, sedimentary islands and by geological barriers..
The islands have great biological importance, given the geographic isolation to which the species that inhabit them are subjected, which promotes the formation of unique species. In addition, oceanic islands have great geostrategic importance, because they provide economic rights over areas of the ocean to the nations that own them..
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An island is any land mass that remains emerged in the middle of a body of water that totally surrounds it. This gives it certain characteristics, which vary depending on whether it is a marine or freshwater island..
Water heats up and cools slower than land and impacts climate, especially on relatively small islands. In such a way that the climate of the islands receives an important influence from the body of water that surrounds it..
For example, as the land loses heat faster than the surrounding water, winds flow from the water to the island carrying moisture. If it is a marine island, these winds will also carry salts, which hinders the development of vegetation..
Whereas in a lake or river, the winds carry moisture lacking in salts, promoting the presence of more vegetation. For its part, the size of the island influences and in large ones the effect of the water mass is not uniform because the effect is less relevant towards the center..
A very outstanding characteristic of the islands from the biological point of view is the amount of endemic species (exclusive to that place). This has to do with the condition of an isolated area, which prevents the species of the island from interbreeding with the continental ones. So after millions of years, new species appear that are genetically incompatible with their distant sister species..
From a geostrategic point of view, islands have a lot of value, because they extend the marine borders of a country. This is because according to international agreements, every nation has sovereignty over 200 nautical miles calculated from its land possessions..
For example, Isla de Aves is an islet measuring 375 m by 50 m at 4 meters above sea level, located 520 km off the Venezuelan coast. In fact, in very strong storms it is completely submerged, except for the Venezuelan navy station that is on stilts..
However, this piece of land provides Venezuela with an exclusive economic zone of 200 miles around the island in the middle of the Caribbean Sea..
The islands originate through very diverse processes, and can arise when the body of water is formed or later. In the first case, the island corresponds to elevated lands, resistant to erosion, which are maintained when rivers, lakes or penetrate the sea..
Likewise, islands can be originated by processes subsequent to the formation of the body of water, such as sedimentation, volcanism or biological activity..
Many islands found on the continental shelves were elevations on the continental coastal edges of the past. As the sea level increased, it flooded the low areas, remaining elevated areas like islands..
Likewise, in the courses and mouths of rivers, there are islands that are formed by a similar process, since there are elevated areas that are not covered by the river. This can occur due to its elevation or geological conformation, which generates an erosion-resistant front that diverts the current of the river..
This process occurs in rivers and lakes, as a result of the accumulation of sediments carried by water currents. As sediments accumulate in a certain area, they end up emerging and islands are formed..
These islands can be temporary and disappear or they can be consolidated to be permanent. Here the vegetation plays an important role, whose roots consolidate the land and reduce the loss of substrate due to erosion..
Underwater volcanoes expel lava that solidifies and rises in level, so that over time the top can emerge and create an island. This process of island formation can occur in both oceans and large lakes..
The activity of the colonies of coral polyps with their calcareous covers, are the cause of the formation of islands. This occurs by simple accumulation and horizontal and vertical growth of the coral colony in shallow marine waters..
Later, the colony can emerge and although the coral polyps die, their calcareous structures persist and form an island.
The island differs from the continents by its size, although the criterion is somewhat subjective, because the continents are also land masses surrounded by water on all sides. Thus, Australia with an area of almost 8,000,000 kmtwo is considered a continent, while Greenland with 2,000,000 kmtwo is defined as an island.
Due to their size there are islands and islets or keys, the latter being very small islands not permanently inhabited. Regarding their place of appearance, they are marine, lacustrine or riparian.
The islands are also classified according to their geographical location in relation to the continental masses. In this case, we speak of oceanic islands when they are not part of the continental shelf and continental islands when they are associated with the continent..
While due to its geological origin there are continental, volcanic, coral, sedimentary, mud volcano and mixed islands. This classification is the most widespread to differentiate the islands and we detail them below:
The continental islands from the geological point of view are constituted by the same material of the continent from which they originated. In addition, they are part of the continental shelf, being separated from the continental mass by a shallow portion of water, less than 200 m.
In fact, in geological periods when the sea level was much lower than it is today, they were part of the continent. Examples of continental islands are the island of Margarita (Venezuela), which is part of the South American continental shelf.
Likewise, the British Isles are a continuity of the European continental shelf and the island of Madagascar in southeast Africa, is a continental island, although its origin is from the old continent Gondwana. This old continent when splitting gave rise to South America, Africa, India, Australia and the island of Madagascar.
These islands are formed from underwater volcanoes that, due to successive eruptions, raise their height due to the accumulation of lava until they emerge and form islands. An example are the lacustrine islands of the Great Lake of Nicaragua and oceanic islands such as those of Hawaii..
There are different types of volcanic islands depending on the process that gives rise to them, such as subduction, when a marine geological plate sinks and melts under a continental plate. This causes volcanic activity and islands can form, such as many islands in the Lesser Antilles..
On the other hand, islands can arise from volcanoes located in the oceanic ridges, such as the island of Iceland in the Atlantic..
There are also volcanic islands that arise in so-called hot spots, which are areas in the middle of an oceanic geological plate. An example of this type of islands are those of Cape Verde on the African plate and the Hawaiian islands on the Pacific plate..
These originate from the accumulation of calcareous material generated by coral reefs, that is, they are biological products. Coral polyps are colony-forming organisms with calcareous covers.
Since corals require waters above 20ºC, these islands only form in tropical or subtropical seas. Corals when reaching the surface die and do not continue to grow, so these islands are usually flat, such as the Maldives and the archipelago of Los Roques (Venezuela).
These are islands that are formed mainly at the mouth of rivers or in their middle part by accumulation of sediments carried by the river itself. In particular cases, they can be formed by the emergence of masses of mud pushed by gases (mud volcanoes), as in the delta of the Orinoco river in northeast Venezuela..
Unlike sedimentary islands, they are not formed by accumulation of sediments, but by the presence of a geological barrier. That is, the course of the river meets a non-erodible obstacle and forks or meanders, leaving islands in its path..
Examples of this type are the island of Bananal in the Araguaia river (Brazil) and the island of La Cité in the Seine river (France).
These are islands in whose formation various processes are combined, such as islands on continental shelves with volcanic action. Another type are initially volcanic islands combined with coral action. An example of mixed islands is the archipelago of Japan formed on a continental fragment by volcanic action..
It is the largest existing island, reaching around 2,166,086 kmtwo, being a continental island located between the Atlantic Ocean and the Arctic. It is continental because its geological base is part of the Canadian Shield (North American platform).
This island is 80% covered with ice, making it the second frozen freshwater reserve after Antarctica..
It is the largest river island in the world reaching 20,000 kmtwo and it is found in Brazil between the Araguaia and Javaés rivers. It is really the same Araguaia river that, when facing the geological barrier of the land, separates into two arms, forming the island.
In this case, one of the arms is considered another river, the Javaés, which 500 km later converges again with the Araguaia. This island located in the tropical zone harbors a great biological diversity, since it is in the transition between the Amazon and the Brazilian Cerrado.
This archipelago of more than 150 islands is located in the northwestern Atlantic Ocean off the east coast of the United States. Its origin is mixed, mainly volcanic, to which the coral action was later added..
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