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.
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 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
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
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.
Technical limitations of defining "islands"
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.
See also
- 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
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.
- Island Resources
- Definition of island and pictures
- Information on how islands are made