Island

A small island

An island is any piece of land smaller than a continent and larger than a rock that is completely surrounded by water. Very small islands — say, islands smaller than necessary for most useful purposes — are called islets. Although seldom adhered to, it is also proper to call an emergent land feature on an atoll an islet, since an atoll is a type of island.

List of islands provides a listing of the larger islands of the earth.

There are three general types of islands: continental, river, and volcanic.

Continental islands

Continental islands are islands that are connected by the continental shelf to 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, 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: accumulations 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, that have developed vegetation.

Volcanic islands

Volcanic islands are built by volcanoes. Mid-ocean examples are not geologically 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 Marianas Islands, the Aleutian Islands, and most of Tonga in the Pacific Ocean. Only some of the Lesser Antilles and the South Sandwich Islands are the only Atlantic examples.

Another type of volcanic island occurs where a mid-ocean rift reaches the surface. There are two examples: Iceland, which is the world's largest volcanic island, and Jan Mayen.

The last type of volcanic island are those formed over hot spots. The hot spot is stationary relative to the plate above it, so it leaves a chain of islands as the plate slowly 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. An example is the Hawaiian Islands, from Hawaii to Kure, which extends benearth the sea surface northward as the Emperor Seamounts. Another similarly oriented chain is the Tuamotu Archipelago; its bend becomes the Line Islands. The southernmost chain is the Austral Islands, with its northern branch as most of the atolls in the nation of Tuvalu. Tristan da Cunha is an example from the Atlantic Ocean.

• See also: atoll; reef; volcanic island; archipelago; Geography.

Island is also a novel by Aldous Huxley

Island is the name of a commune in the Yonne département in France.

Referenced By