Island
This article possibly contains original research. (December 2021) |
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 two main types of islands in the sea: continental islands and oceanic islands. There are also artificial islands (man-made islands).
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
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]
By contrast, islands are usually seen as being extensions of the oceanic crust (e.g. volcanic islands), or as belonging to a continental plate containing a larger landmass (continental islands); the latter is the case of Greenland, which sits on the North American Plate.[10]
Continental islands
Continental islands are bodies of land that lie on the
Microcontinental islands
A special type of continental island is the microcontinental island, which is created when a continent is horizontally displaced or rifted.[12][13] Examples are Madagascar and Socotra off Africa, New Caledonia, New Zealand, and some of the Seychelles.[13]
Subcontinental islands
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:
- barrier islands, which are accumulations of sand deposited by sea currents on the continental shelves[15][16]
- 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]
Oceanic islands
Oceanic islands are typically considered to be islands that do not sit on
Tectonic
The few oceanic islands that are not volcanic are tectonic in origin and arise where plate movements have lifted up the ocean floor above the surface. Examples are the Saint Peter and Saint Paul Archipelago in the North Atlantic Ocean and Macquarie Island in the South Pacific Ocean.
Volcanic islands
Arcs
One type of volcanic oceanic island is found in a volcanic island arc. These islands arise from volcanoes where the subduction of one plate under another is occurring. Examples are the Aleutian Islands, the Mariana Islands, and most of Tonga in the Pacific Ocean.[21][22] The only examples in the Atlantic Ocean are some of the Lesser Antilles and the South Sandwich Islands.
Oceanic rifts
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.
Hotspots
A third type of volcanic oceanic island is formed over volcanic hotspots. A
Atolls
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]
Tropical islands
Approximately 45,000 tropical islands with an area of at least 5 hectares (12 acres) exist.[27] Examples formed from coral reefs include Maldives, Tonga, Samoa, Nauru, and Polynesia.[27] Granite islands include Seychelles[28] and Tioman.
The socio-economic diversity of tropical islands ranges from the
De-islanding
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
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.
Artificial islands
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]
Sometimes natural islands are artificially enlarged, such as
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]
Island superlatives
- Largest island: Greenland[36]
- Largest island in a lake: Manitoulin Island, Ontario, Canada[36]
- Largest lake island within a lake island: Treasure Island, in Lake Mindemoya on Manitoulin Island[37]
- Largest island in a river: Bananal Island, Tocantins, Brazil[38]
- Largest island in fresh water: Marajó, Pará, Brazil
- Largest sand island: Fraser Island, Queensland, Australia[39]
- Largest artificial island: Flevopolder, the Netherlands (created 1969)[40]
- Largest uninhabited island: Devon Island, Nunavut, Canada[41]
- Most populous island: Java, Indonesia[42]
- Lowest island: Franchetti Island, Lake Afrera, Ethiopia
- Island shared by largest number of countries: Borneo (Brunei, Indonesia, Malaysia)
- Island with the highest point: New Guinea (Puncak Jaya, 4,884 m, 16,024 ft), Indonesia
- Northernmost island: Kaffeklubben Island, Greenland
- Southernmost island (not fully surrounded by permanent ice): Ross Island, Antarctica
- Island with the most populated city: Honshu (Tokyo), Japan
- Most remote island (from nearest land): Bouvet Island[43]
- Island with earliest known settlement: Lida Ajer cave), Indonesia
See also
- Desert island
- Great wall of sand
- Island biogeography
- Island ecology
- Island country
- Island hopping
- Lake island
- List of ancient islands
- List of archipelagos
- List of artificial islands
- List of divided islands
- List of fictional islands
- List of island countries
- List of islands by area
- List of islands by body of water
- List of islands by continent
- List of islands by country
- List of islands by highest point
- List of islands by name
- List of islands by population
- List of islands by population density
- List of islands named after people
- Phantom island
- Private island
- River island
- Rock fever
- Small Island Developing States
- Tidal island
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- ^ 形形色色的海洋岛屿 (in Chinese)
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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.
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- ^ Wolchover, Natalie (January 24, 2012). "World's Largest Island-in-a-lake-on-an-island-in-a-lake-on-an-island Seen on Google Earth". livescience.com. Archived from the original on April 7, 2022. Retrieved August 20, 2022.
- ^ "Bananal Island". Encyclopædia Britannica (Online ed.). Archived from the original on September 3, 2017. Retrieved August 20, 2022.
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External links
- Definition of island from United Nations Convention on the Law of the Sea
- Listing of islands Archived February 14, 2008, at the Wayback Machine from United Nations Island Directory.