Island
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.
|
Angel Island in the San Francisco Bay |
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 off
Asia,
New Guinea and
Tasmania off
Australia.
A special type of continental island is the
microcontinental island, which results when a continent is
rifted. The best example is
Madagascar off 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 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
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 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
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 down 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.
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
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 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 and
Forth and Clyde canals in
Scotland and the
Volga-Baltic Waterway in
Russia.
This also helps explain why Africa-Eurasia can be seen as one continuous landmass (and thus technically the biggest island): generally the
Suez Canal (yet another example of a coast-to-coast water system) is not seen as something that divides the land mass in two.
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List of islands*
List of islands by name*
List of islands by area*
List of islands by population*
List of islands by highest point*
Island nation*
Reef*
Atoll*
Desert island*
Tidal island*
List of artificial islands*
List of divided islands*
Skerry*
Ait*
List of fictional islands*
Islandlake*
Private island*
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.
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Definition of island and pictures*
Information on how islands are madezh-yue:島
