Everything about Island totally explained
An
island or
isle (/ˈaɪl/) is any piece of land that's completely surrounded by water in two dimensions, above high tide, and isolated from other significant landmasses. Very small islands such as emergent land features on
atolls are called
islets. A
key or
cay is another name for a small island or islet. An island in a river or lake may be called an
eyot, /ˈaɪət/.
There are two main types of islands:
continental islands and
oceanic islands. There are also
artificial islands. A grouping of geographically and/or geologically related islands is called an
archipelago.
The word
island comes from
Old English ī(e)gland (literally, "watery land"). However, the spelling of the word was modified in the 15th century by association with the
etymologically unrelated Old French loanword
isle.
There is no standard of size which distinguishes islands from
islets and
continents.
When defining islands as pieces of land that are completely surrounded by water, narrow bodies of water like
rivers and
canals are generally left out of consideration. For instance, in France the
Canal du Midi connects the
Garonne river to the
Mediterranean Sea, thereby completing a continuous water connection from the
Atlantic Ocean to the Mediterranean Sea. So technically, the land mass that includes the
Iberian Peninsula and the part of France that's south of the Garonne River and the Canal du Midi is completely surrounded by water. For a completely natural example, the
Orinoco River splits into two branches near Tamatama, in Amazonas state, Venezuela. The southern branch flows south and joins the Rio Negro, and then the Amazon. Thus, all of the Guianas (Guyana, Suriname, and French Guiana) and substantial parts of Brazil and Venezuela are surrounded by (river or ocean) water. These instances are not generally considered islands.
This also helps explain why Africa-Eurasia can be seen as one continuous landmass (and thus technically the biggest island): generally the
Suez Canal isn't seen as something that divides the land mass in two.
On the other hand, an island may still be described as such despite the presence of a land bridge, for example,
Singapore and its causeway or the various Dutch delta Islands, such as
IJsselmonde. The retaining of the island description may therefore be to some degree simply due to historical reasons - though the land bridges are often of a different geological nature (for example sand instead of stone), and thus the islands remain islands in a more scientific sense as well.
Types
Continental islands
Continental islands are bodies of land that lie on the
continental shelf of a continent. Examples include
Greenland and
Sable Island off
North America;
Barbados and
Trinidad off
South America;
Great Britain,
Ireland and
Sicily off
Europe;
Sumatra and
Java off
Asia; and
New Guinea,
Tasmania and
Kangaroo Island off
Australia.
A special type of continental island is the
microcontinental island, which results when a continent is
rifted. Examples are
Madagascar off
Africa; the
Kerguelen Islands; and some of the
Seychelles.
Another subtype is an island or
bar formed by deposition of tiny rocks where a water current loses some of its carrying capacity. An example is
barrier islands, which are accumulations of
sand deposited by sea currents on the continental shelf. Another example is islands in
river deltas or in large rivers. While some are transitory and may disappear if the volume or speed of the current changes, others are stable and long-lived.
Oceanic islands
Oceanic islands are ones that don't sit on continental shelves. They are
volcanic in origin. One type of oceanic island is found in a
volcanic island arc. These islands arise from volcanoes where the
subduction of one plate under another is occurring. Examples include the
Mariana Islands, the
Aleutian Islands and most of
Tonga in the
Pacific Ocean. Some of the
Lesser Antilles and the
South Sandwich Islands are the only Atlantic Ocean examples.
Another type of oceanic island occurs where an
oceanic rift reaches the surface. There are two examples:
Iceland, which is the world's largest volcanic island, and
Jan Mayen — both are in the Atlantic.
A third type of oceanic island is formed over volcanic
hotspots. A hotspot is more or less stationary relative to the moving
tectonic plate above it, so a chain of islands results as the plate drifts. Over long periods of time, this type of island is eventually eroded and "drowned" by
isostatic adjustment, becoming a
seamount. Plate movement across a hot-spot produces a line of islands oriented in the direction of the plate movement. An example is the
Hawaiian Islands, from
Hawaii to
Kure, which then extends beneath the sea surface in a more northerly direction as the
Emperor Seamounts. Another chain with similar orientation is the
Tuamotu Archipelago; its older, northerly trend is the
Line Islands. The southernmost chain is the
Austral Islands, with its northerly trending part the atolls in the nation of
Tuvalu.
Tristan da Cunha is an example of a hotspot volcano in the Atlantic Ocean. Another hot spot in the Atlantic is the island of
Surtsey, which was formed in 1963.
An atoll is an island formed from a
coral reef that has grown on an eroded and submerged volcanic island. The reef rises to the surface of the water and forms a new island. Atolls are typically ring-shaped with a central
lagoon. Examples include the
Maldives in the
Indian Ocean and
Line Islands in the Pacific.
Further Information
Get more info on 'Island'.
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