Island

An island or isle is any piece of land smaller than a continent and larger than a rock that is completely surrounded by water. Very small islands 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. A key or cay is also another name for a relatively small island. Groups of related islands are called archipelagos.

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 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.

Related Topics:
Volcanic island - Volcano - Mariana Islands - Aleutian Islands - Tonga - Pacific Ocean - Lesser Antilles - South Sandwich Islands - Atlantic Ocean

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

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.

Related Topics:
Oceanic rift - Iceland - Jan Mayen

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

The last type of volcanic island are those formed over volcanic 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 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.

Related Topics:
Hotspot - Tectonic plate - Isostatic adjustment - Seamount - Hawaiian Islands - Hawaii - Kure - Emperor Seamounts - Tuamotu Archipelago - Line Islands - Austral Islands - Tuvalu - Tristan da Cunha - Atlantic Ocean

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

An atoll is an island formed from a coral reef that has grown on an eroded and submerged volcanic island. The reef rises above the surface of the water and forms a new island. Atolls are typically ring-shaped with a central, shallow lagoon. Examples include the Maldives in the Indian Ocean and Bora Bora in the Pacific.

Related Topics:
Atoll - Coral reef - Lagoon - Maldives - Indian Ocean - Bora Bora - Pacific

~ ~ ~ ~ ~ ~ ~ ~ ~ ~