An island in the
Seine river (France)
An
island () or
isle () is any piece of land that is surrounded by water. 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, .
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 igland (from 'ig', similarly meaning 'island' when used independently, and -land carrying its contemporary meaning). However, the spelling of the word was modified in the 15th century by association with the
etymologically unrelated Old French loanword
isle, which itself comes from the latin word
insula.
Characteristics
There is no standard of size which distinguishes islands from
islets and
continents.
When defining islands as pieces of land that are surrounded by water, narrow bodies of water like
rivers and
canals are often, but not always, 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 is south of the Garonne River and the Canal du Midi is 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. However, small pieces of land bordered by rivers are 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 is not seen as something that divides the land mass in two. The mainland of Australia is often considered the largest island because it is covered on all sides by water while not being connected to another body of land.
On the other hand, an island may still be described as such despite the presence of a land bridge, e.g.,
Singapore and its causeway or the various Dutch delta Islands, such as
IJsselmonde. Some places may even retain "island" in their names after being connected to a larger landmass by a wide land bridge, such as
Coney Island. 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 of Island
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,
Borneo 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 and
Socotra off
Africa;
New Zealand; 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.
Islets are very small islands.
Oceanic islands
The islands of
Hawai'i are volcanic islands.
Oceanic islands are ones that do not sit on continental shelves. The vast majority are
volcanic in origin. The few oceanic islands that are not volcanic are tectonic in origin and arise where plate movements have lifted up the deep ocean floor to above the surface. Examples of this include
Saint Peter and Paul Rocks in the Atlantic Ocean and
Macquarie Island in the Pacific.
One type of volcanic 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 volcanic oceanic island occurs where an
oceanic rift reaches the surface. There are two examples:
Iceland, which is the world's second largest volcanic island, and
Jan Mayen — both are in the Atlantic.
A third type of volcanic 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 "drowned" by
isostatic adjustment and eroded, 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.
Tropical islands
There are approximately 45,000
tropical islands on Earth.
Among
coral tropic islands for example are
Maldives,
Tonga,
Nauru and
Polynesia.
islands include
Seychelles and
Tioman.
The socio-economic diversity of these regions ranges from the
Stone Age societies in the interior of
Madagascar,
Borneo or
Papua New Guinea to the high-tech lifestyles of the city-islands of
Singapore and
Hong Kong. The international tourism is a significant factor in the local economy of Seychelles,
Sri Lanka,
Mauritius,
Réunion or
Hawaii.
See also
