Islands can nourish life, or destroy it, by erupting hot lava.
Islands are bodies of land surrounded entirely by water. Some form on their own accord following volcanic activity below the sea, while others break off continents to become separate land masses. Islands exist in a variety of types and are home to many different lifeforms.
Continental
Unlike all other island types, which originate from the ocean floor, continental islands are comprise pieces of the continental crust that have broken away from a larger continent and drifted away at sea. Since these islands are comprise different pieces of continental crust, they contain many different types of rocks and soils and are quite complex in structure. They may also be home to the plant and animal species that lived on the continent to which the pieces that comprise them were formerly attached. Some examples of continental islands include the Sumatra, Sicily and Barbados islands.
Oceanic
Any island that arises from the deep sea floor is termed an oceanic island. While continental islands contain the plant and animal species of a nearby continent, an oceanic island acquires its own unique combination of plants and animals. Some exhibit volcanic activity, while many were once home to active volcanoes that have since become inactive. Oceanic islands vary greatly in size -- some are composed of only a view specks of rock or sand, while others, such as Iceland, are huge land masses. Other oceanic islands include Hawaii and the Azores.
Volcanic
All islands, with the exception of continental islands, start off as volcanoes, although not all possess any remaining volcanic rock today. Volcanic islands start off as submarine volcanoes, which erupt beneath the water. Once a submarine volcano grows large enough that it is visible above ocean surface, it is termed a volcanic island. Young volcanic islands are cone-shaped and frequently erupt lava. As a volcanic island ages and becomes less active, it will begin to erode, resulting in an island with jagged mountains, numerous valleys, and steep slopes at its center; at this point, a coral reef begins to form around the island. The volcanic island will continue to erode, until it disappears.
Coral
While a volcanic island in a tropical body is eroding away, a coral reef is growing around it and turning it into a coral island. During storms, materials pile up on an emerging coral reef, resulting in areas of land on the reef. Coral islands are composed almost exclusively of calcium carbonate or limestone from sand and coral rock made of the skeletons of shells, algae and corals. Famous coral islands include the Great Barrier Reef in Australia and the Belize Barrier Reef in Mexico.
Tags: continental islands, volcanic island, coral reef, islands include, animal species, Barrier Reef, continental crust
