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An artificial island or man-made island is an island that has been constructed by people rather than formed by natural means. They are created by expanding existing islets, construction on existing reefs, or amalgamating several natural islets into a bigger island.
Early artificial islands included floating structures in still waters, or wooden or megalithic structures erected in shallow waters (e.g., crannógs and Nan Madol discussed below). In modern times artificial islands are usually formed by land reclamation, but some are formed by the incidental isolation of an existing piece of land during canal construction (e.g. Donauinsel and Dithmarschen), or flooding of valleys resulting in the tops of former knolls getting isolated by water (e.g. Barro Colorado Island). The largest artificial island, René-Levasseur Island, was formed by flooding of two adjacent reservoirs.
Artificial islands may vary in size from small islets reclaimed solely to support a single pillar of a building or structure, to those that support entire communities and cities.
Despite a popular image of modernity, artificial islands actually have a long history in many parts of the world, dating back to the crannogs of prehistoric Scotland and Ireland, the ceremonial centers of Nan Madol in Micronesia and the still extant floating islands of Lake Titicaca. The city of Tenochtitlan, the Aztec predecessor of Mexico City that was home to 500,000 people when the Spaniards arrived, stood on a small natural island in Lake Texcoco that was surrounded by countless artificial chinamitl islands.
Many artificial islands have been built in urban harbors to provide either a site deliberately isolated from the city or just spare real estate otherwise unobtainable in a crowded metropolis. An example of the first case is Dejima (or Deshima), created in the bay of Nagasaki in Japan's Edo period as a contained center for European merchants. During the isolationist era, Dutch people were generally banned from Nagasaki and Japanese from Dejima. Similarly, Ellis Island, in Upper New York Bay beside New York City, a former tiny islet greatly expanded by Land Reclamation, served as an isolated immigration center for the United States in the late 19th and early 20th century, preventing an escape to the city of those refused entry for disease or other perceived flaws, who might otherwise be tempted toward illegal immigration. One of the most well-known artificial islands is the Île Notre-Dame in Montreal, built for Expo 67.
The Venetian Islands in Miami Beach, Florida, in Biscayne Bay added valuable new real estate during the Florida land boom of the 1920s. When the bubble that the developers were riding burst, the bay was left scarred with the remnants of their failed project. A boom town development company was building a sea wall for an island that was to be called Isola di Lolando but could not stay in business after the 1926 Miami Hurricane and the Great Depression, dooming the island-building project. The concrete pilings from the project still stand as another development boom roared around them, 80 years later.
Largest artificial islands according to their size (reclaimed lands)
|2||Yas Island||25||Abu Dhabi, UAE||Racing circuit|
|3||Hong Kong International Airport||9.4||China||Airport|
|4||Kansai International Airport||8.1||Japan||Airport|
|5||Palm Jebel Ali||8||Dubai, UAE||on hold|
|6||Chūbu Centrair International Airport||6.8||Japan||Airport|
|7||Palm Jumeirah ||6.5 ||Dubai, UAE||Housing|
|10||Kansai International Airport||4.0||Japan||Airport|
In 1969, the Flevopolder in the Netherlands was finished, as part of the Zuiderzee Works. This island consists of the polders Eastern Flevoland and Southern Flevoland, and has a total land surface of 970 km², which makes it by far the largest artificial island in the world.
Dubai is home to several artificial island projects. They include the Palm Islands projects (Palm Jumeirah, Palm Jebel Ali, and Palm Deira); and The World, The Universe and the Dubai Waterfront. Of all these, only the Palm Jumeirah is complete and inhabited so far. Also, the Burj Al Arab is on its own artificial island.  The Universe, Palm Jebel Ali, Dubai Waterfront, and Palm Deira are on hold.
Kansai International Airport is the first airport to be built completely on an artificial island in 1994, followed by Chūbu Centrair International Airport in 2005 and the New Kitakyushu Airport and Kobe Airport in 2006. When Hong Kong International Airport opened in 1998, 75% of the property was created using Land reclamation upon the existing islands of Chek Lap Kok and Lam Chau.
Under the United Nations Convention on the Law of the Sea treaty (UNCLOS), artificial islands are not considered harbor works (Article 11) and are under the jurisdiction of the nearest coastal state if within 200 nautical miles (370 km) (Article 56). Artificial islands are not considered islands for purposes of having their own territorial waters or exclusive economic zones, and only the coastal state may authorize their construction (Article 60); however, on the high seas beyond national jurisdiction, any "state" may construct artificial islands (Article 87).
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