An island or isle is a piece of subcontinental land completely surrounded by water. Very small islands such as emergent land features on atolls can be called islets, skerries, cays or keys. An island in a river or a lake island may be called an eyot or ait, and a small island off the coast may be called a holm. Sedimentary islands in the Ganges Delta are called chars. A grouping of geographically or geologically related islands, such as the Philippines, is referred to as an archipelago.
There are about 900,000 official islands in the world. This number consists of all the officially-reported islands of each country. The total number of islands in the world is unknown. There may be hundreds of thousands of tiny islands that are unknown and uncounted.[1] The number of sea islands in the world is estimated to be more than 200,000. The total area of the world's sea islands is approx. 9,963,000 km2, which is similar to the area of Canada and accounts for roughly 1/15 (or 6.7%) of the total land area of Earth.[2]
Etymology
The word island derives from Middle Englishiland, from Old Englishigland (from ig or ieg, similarly meaning 'island' when used independently, and -land carrying its contemporary meaning; cf. Dutcheiland ("island"), GermanEiland ("small island")).The spelling of the word was modified in the 15th century because of a false etymology caused by an incorrect association with the etymologically unrelated Old French loanword isle, which itself comes from the Latin word insula.[3][4]Old Englishieg is actually a cognate of Swedishö and GermanAue, and more distantly related to Latin aqua (water).[5]
Relationships with continents
Differentiation from continents
There is no standard of size that distinguishes islands from continents,[6] or from islets.[7]
There is a widely accepted difference between islands and continents in terms of geology.[8] Continents are often considered to be the largest landmass of a particular continental plate; this holds true for Australia, which sits on its own continental lithosphere and tectonic plate (the Australian Plate).[9]
A lake such as Wollaston Lake drains in two different directions, thus creating an island. If this island has a seashore as well as being encircled by two river systems, it becomes what might be called a subcontinental island. The one formed by Wollaston Lake is very large, about 2,000,000 km2 (770,000 sq mi).[14]
Bars
Another subtype is an island or bar formed by deposition of tiny rocks where water current loses some of its carrying capacity. This includes:
fluvial or alluvial islands formed in river deltas or midstream within large rivers. While some are transitory and may disappear if the volume or speed of the current changes, others are stable and long-lived.[17]
Another type of volcanic oceanic island occurs where an oceanic rift reaches the surface. There are two examples: Iceland, which is the world's second-largest volcanic island, and Jan Mayen. Both islands are in the Atlantic Ocean.
A third type of volcanic oceanic island is 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 "drowned" by isostatic adjustment and eroded, becoming a seamount.[23] 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 continue 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.[24] Another hotspot in the Atlantic is the island of Surtsey, which was formed in 1963.[25]
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 are the Line Islands in the Pacific Ocean and Maldives in the Indian Ocean.[26]
The process of de-islandisation is often concerning bridging, but there are other forms of linkages such as causeways: fixed transport links across narrow necks of water, some of which are only operative at low tides (e.g. that connecting Cornwall's St Michael's Mount to the peninsular mainland), while others (such as the Canso Causeway connecting Cape Breton to the Nova Scotia mainland) are usable all year round (aside from interruptions during storm surge periods).[30][31]
Some places may retain "island" in their names for historical reasons after being connected to a larger landmass by a land bridge or landfill, such as Coney Island and Coronado Island, though these are, strictly speaking, tied islands.[31] Conversely, when a piece of land is separated from the mainland by a man-made canal, for example the Peloponnese by the Corinth Canal, more or less the entirety of Fennoscandia by the White Sea Canal, or Marble Hill in northern Manhattan during the time between the building of the United States Ship Canal and the filling in of the Harlem River which surrounded the area, it is generally not considered an island.
Another type of connection is fostered by harbor walls/breakwaters that incorporate offshore islets into their structures, such as those in Sai harbor in northern Honshu, Japan, and the connection to the mainland which transformed Ilhéu do Diego from an islet. De-islanded through its fixed link to the mainland, the former islet's name, Ilhéu do Diego, became functionally redundant (and thereby archaic) and the location took the fort as its namesake. Some former island sites have retained designations as islands after the draining/subsidence of surrounding waters and their fixed linkage to land (England's Isle of Ely and Vancouver's Granville Island being respective cases in point). Their names are thereby archaic in that they reflect the islands' pasts rather than their present structures or transport logistics. Other examples include Singapore and its causeway, and the various Dutch delta islands, such as IJsselmonde.
Almost all of Earth's islands are natural and have been formed by tectonic forces or volcanic eruptions. However, artificial (man-made) islands also exist, such as the island in Osaka Bay off the Japanese island of Honshu, on which Kansai International Airport is located. Artificial islands can be built using natural materials (e.g., earth, rock, or sand) or artificial ones (e.g., concrete slabs or recycled waste).[32][33]
Artificial islands are sometimes built on pre-existing "low-tide elevation," a naturally formed area of land which is surrounded by and above water at low tide but submerged at high tide. Legally these are not islands and have no territorial sea of their own.[35]
^Ringe, Donald A. (2006). A Linguistic History of English: From Proto-Indo-European to Proto-Germanic. Oxford University Press. p. 109. ISBN0-19-928413-X.
^Cunningham, John M. "Is Australia an Island?". Encyclopædia Britannica (Online ed.). Archived from the original on January 25, 2019. Retrieved August 20, 2022.
^"Continent". National Geographic. National Geographic Society. Archived from the original on July 16, 2019. Retrieved August 20, 2022.
^"Island". National Geographic Society. August 27, 2012. Archived from the original on June 17, 2021. Retrieved May 2, 2022.
^"Island (geography)". Encyclopædia Britannica. Archived from the original on October 8, 2014. Retrieved September 16, 2014.
^Zug, George R. (2013). Reptiles and Amphibians of the Pacific Islands: A Comprehensive Guide. University of California Press.
^"Origin of Bermuda and its Caves". Ocean Explorer. U.S. NOAA. United States Department of Commerce. 2009. Archived from the original on March 20, 2021. Retrieved September 10, 2021. Extending toward the ocean's surface are four northeast-to-southwest trending volcanic peaks, including the emergent Bermuda Pedestal and the submerged Challenger, Argus, and Bowditch seamounts (figure 1). The islands of Bermuda are located along the southeast margin of the largest peak, the Bermuda Pedestal.
^Arnberger, Hertha, Erik (2011). The Tropical Islands of the Indian and Pacific Oceans. Vienna: Austrian Academy of Sciences Press. ISBN978-3-7001-2738-3.{{cite book}}: CS1 maint: multiple names: authors list (link)