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Island
*** Shopping-Tip: Island
{{otheruses}}
image:Island.jpg right|thumb|400px|A small island in the [[Adriatic Sea]]
An '''island''' or '''isle''' is any piece of land that is completely surrounded by water. Very small islands are called '''
islets'''. It is also proper to call an emergent land feature on an
atoll an '''islet''', since an atoll is a type of island, although this convention is seldom adhered to. A '''key''' or '''cay''' is another name for a relatively small island or islet. The word ''island'' derives ultimately from the
Old English word ''igland''. It was originally spelled phonetically: ''iland''. The letter "s" was added out of a mistaken belief that the word derived from ''isle'' (<
Old French <
Latin ''insula'') + ''land'', although no such etymological relationship existed.
There are three main types of islands: '''continental''' islands, '''river''' islands, and '''volcanic''' islands. There are also human-made or
artificial islands. A grouping of related islands is called an
archipelago.
Continental islands
Continental islands are bodies of land that lie upon the
continental shelf of a continent. Examples include
Greenland and
Sable Island off
North America,
Barbados and
Trinidad off
South America,
Sicily off
Europe,
Sumatra and
Java (island) Java off
Asia,
New Guinea and
Tasmania off
Australia.
A special type of continental island is the '''microcontinental island''', which results when a continent is
rift (geology) rifted. The best example is
Madagascar off of Africa. The
Kerguelen Islands and some of the
Seychelles are also examples.
Another subtype is the '''
barrier island''': an accumulation of
sand on the continental shelf.
River islands
River islands occur in
river deltas and in large
rivers. They are caused by deposition of sediment at points in the flow where the current loses some of its carrying capacity. In essence, they are river
bar (landform) bars, isolated in the stream. While some are ephemeral, and may disappear if the river's water volume or speed changes, others are stable and long-lived.
Volcanic islands
Image:STS61A-50-57.jpg right|thumb|[[Hawaii (island) is a volcanic island.]]
Image:Wake Island.png right|thumb|[[Wake Island is a volcanic island that has become an
atoll. ]]
Volcanic islands are built by
volcanoes. Mid-ocean examples are not part of any continent. One type of volcanic 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,
Republic of Mauritius 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 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 volcanic island are those formed over volcanic
Hotspot (geology) hotspots. A hot spot 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 down and "drowned" by
isostasy 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 Atoll 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
Surtsey.
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 Ocean Pacific.
Some technical limitations to the concept "island"
There is no standard of size which distinguishes islands from
islets and
continents. Many elementary school children, when first learning geographical terms such as these, correctly point out that all continents are surrounded by water too, and are thus technically islands themselves. As such, the largest island in the world is actually the super-continent of
Africa-Eurasia.
Also, when defining islands as pieces of land that are completely surrounded by water, narrow bodies of water like
river rivers and
canal 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 Iberian peninsula and the part of France that is south of the Garonne river and the Canal du Midi is completely surrounded by water. However, generally cases such as these are not considered islands. Other examples of such coast-to-coast watersystems that are not considered to cut a land mass in two are the
Caledonian Canal and the
Forth-to-Clyde waterway in Great Britain, and the
Volga-Baltic_Waterway Volga-Baltic Waterway in Rusland.
This also helps explain why Africa-Eurasia can be seen as one continues landmass (and thus technically the biggest island): generally the
Suez_canal Suez-canal (yet another example of a coast-to-coast water system) is not seen as something that divides the land mass in two.
See also
{{commons|Island}}
*
List of islands
*
List of islands by area
*
List of islands by population
*
Island nation
*
Reef
*
Desert island
*
Tidal island
*
List of artificial islands
*
List of divided islands
*
Skerry
*
Ait
*
List of fictional islands
*
Islandlake
External links
-
Definition of island from
United Nations Convention on the Law of the Sea
-
Listing of islands from
United Nations Island Directory. Very comprehensive listing of all islands in the world with lots of information related to environmental issues.
Category:Islands
Category:Landforms
af:Eiland
ar:جزيرة
bg:ОÑ?тров
zh-min-nan:Tó-sū
bs:Otok
ca:Illa
cs:Ostrov
da:Ø
de:Insel
et:Saar
es:Isla
eo:Insulo
fr:ÃŽle
gl:Illa
ko:섬
ku:Girav
hr:Otok
io:Insulo
id:Pulau
is:Eyja
it:Isola
he:×?×™
mk:ОÑ?тров
ms:Pulau
nl:Eiland
nds:Insel
ja:島
lb:Insel
no:Øy
nn:Øy
os:Сакъадах
pl:Wyspa
pt:Ilha
ro:Insulă
rm:Insla
ru:ОÑ?тров
simple:Island
sl:Otok
sr:ОÑ?трво
fi:Saari
sv:Ö (land)
tl:Pulo
th:เ�าะ
to:Motu
tpi:Ailan
tr:Ada
uk:ОÑ?трів
zh:島嶼
zh-yue:島
*** Shopping-Tip: Island
