User:ForksForks/sandbox/Island

An island or isle is a piece of subcontinental land completely surrounded by water.

Definition

This is the definition of an island. The etymology ought to go here too.

https://www.britannica.com/science/island#ref234009

https://www.britannica.com/story/is-australia-an-island

https://education.nationalgeographic.org/resource/Continent/

Geology

Formation in oceans

Islands often are found in archipelagos, or island chains. These chains are thought to form from volcanic hotspots, areas of the lithosphere where the mantle is hotter than the surrounding area. These hotspots would give rise to volcanoes whose lava would form the rock the islands are made of. For some islands, the movement of tectonic plates above stationary hotspots would form islands in a linear chain, with the islands further away from the hotspot being progressively older and more eroded, before disappearing under the sea entirely. An example is the Hawaiian Islands, with the oldest island Kure Atoll being 25 million years old, and the youngest, Hawaii, still being an active volcano. However, not all island chains are formed this way. Some may be formed all at once by fractures in the tectonic plates themselves simultaneously creating multiple islands. One supporting piece of evidence is that of the Line Islands, which are all estimated to be 8 million years old, rather than being different ages.

Other island chains form due to being separated from existing continents. The Japanese archipelago may have been separated from Eurasia due to seafloor spreading, a phenomenon where new oceanic crust is formed, pushing away older crust. Other islands, like those that make up New Zealand, are what remains of continents that shrank and sunk beneath the sea. It was estimated that Zealandia, the continent-like area of crust that New Zealand sits on, has had 93% of its original surface area submerged.

Some islands are formed when coral reefs grow on volcanic islands that have submerged beneath the surface. When these coral islands encircle a central lagoon, the island is known as an atoll. The formation of reefs and islands related to those reefs is aided by the buildup of sediment in shallow patches of water. In some cases, tectonic movements lifting a reef out of the water by as little as 1 meter can cause sediment to accumulate and an island to form.