Difference between revisions of "Island" - New World Encyclopedia

From New World Encyclopedia
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[[Image:Mokuaeae island.jpg|right|thumb|300px|Mokuaeae Island, off Kilauea Point, Kauai, Hawaii.]]  
 
[[Image:Mokuaeae island.jpg|right|thumb|300px|Mokuaeae Island, off Kilauea Point, Kauai, Hawaii.]]  
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[[Image:Manhattan.jpg|thumb|300px|Manhattan Island, New York. One of the world's most densely populated islands at 67,000 residents per square mile.]]
 
[[Image:Manhattan.jpg|thumb|300px|Manhattan Island, New York. One of the world's most densely populated islands at 67,000 residents per square mile.]]
  
There is no standard of size which distinguishes islands from [[islet]]s and [[continent]]s. Any landmass surrounded by water could be considered an island. Under this terminology all the land masses on the [[planet]] could be considered islands.
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An island is any area of land which is smaller than a continent and is entirely surrounded by water and my occur in [[ocean]]s, [[sea]]s, [[lake]]s, or [[river]]s. Islands closely grouped together are called an archipelago.  
  
Also, when defining islands as pieces of land that are completely surrounded by water, narrow bodies of water like [[river]]s and [[canal]]s are generally left out of consideration{{Fact|date=February 2007}}. For instance, in France the [[Canal du Midi]] connects the [[Garonne]] river to the [[Mediterranean Sea]], thereby completing a continuous water connection from the [[Atlantic Ocean]] to the Mediterranean Sea. So technically, the land mass that includes the [[Iberian Peninsula]] and the part of France that is south of the Garonne River and the Canal du Midi is completely surrounded by water. For a completely natural example, the [[Orinoco]] River splits into two branches near Tamatama, in Amazonas state, Venezuela. The southern branch flows south and joins the Rio Negro, and then the Amazon. Thus, all of the Guianas (Guyana, Suriname, and French Guiana) and substantial parts of Brazil and Venezuela are surrounded by (river or ocean) water. These instances are not generally considered islands.
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There is no standard of size which distinguishes islands from [[islet]]s and [[continent]]s. Any landmass surrounded by water could be considered an island. Under this terminology all the land masses on the [[planet]] could be considered islands.
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Often when defining islands as pieces of land that are completely surrounded by water, narrow bodies of water like [[river]]s and [[canal]]s are generally left out of consideration. For instance, in France the [[Canal du Midi]] connects the [[Garonne]] river to the [[Mediterranean Sea]], thereby completing a continuous water connection from the [[Atlantic Ocean]] to the Mediterranean Sea. So technically, the land mass that includes the [[Iberian Peninsula]] and the part of France that is south of the Garonne River and the Canal du Midi is completely surrounded by water. For a completely natural example, the [[Orinoco River]] splits into two branches near Tamatama, in Amazonas state, Venezuela. The southern branch flows south and joins the Rio Negro, and then the Amazon. Thus, all of the Guianas (Guyana, Suriname, and French Guiana) and substantial parts of [[Brazil]] and [[Venezuela]] are surrounded by (river or ocean) water. These instances are not generally considered islands.
  
 
This also helps explain why Africa-Eurasia can be seen as one continuous landmass (and thus technically the biggest island): generally the [[Suez Canal]] is not seen as something that divides the land mass in two.
 
This also helps explain why Africa-Eurasia can be seen as one continuous landmass (and thus technically the biggest island): generally the [[Suez Canal]] is not seen as something that divides the land mass in two.
  
On the other hand, an island may still be described as such despite the presence of a land bridge, e.g., [[Singapore]] and its causeway or the various Dutch delta Islands, such as [[IJsselmonde (island)|IJsselmonde]]. The retaining of the island description may therefore be to some degree simply due to historical reasons - though the land bridges are often of a different geological nature (for example sand instead of stone), and thus the islands remain islands in a more scientific sense as well.
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On the other hand, an island may still be described as such despite the presence of a land bridge, such as [[Singapore]] and its causeway or the various Dutch delta Islands, such as [[IJsselmonde (island)|IJsselmonde]]. The retaining of the island description may therefore be to some degree simply due to historical reasons - though the land bridges are often of a different geological nature (for example sand instead of stone), and thus the islands remain islands in a more scientific sense as well.
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==Types of islands==
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It is generally accepted that there are two types of islands: ''Oceanic'' and ''Continental''. Continental Islands are thought to have been connected to the nearby continent at some point in time, and separated either recently (in a geologic frame of reference) or in ancient eras. Oceanic Islands are those which were never connected to another body of land but formed in mid-ocean. However, some schools of thought break this into a further categorization, including ''Recent Continental Islands'', ''Ancient Continental Islands'' and ''Oceanic Islands''.
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With the exception of the [[Seychelles Islands]] in the [[Indian Ocean]], Oceanic Islands are always either [[coral]]line or [[volcano|volcanic]] in composition. The geological make-up of Continental Islands resembles that of continents with a variety of formations, most often comprised of varying ages of stratifed rock.
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===HERE===
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=== Continental islands ===
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Continental islands are bodies of land that lie on the [[continental shelf]] of a continent. Examples include [[Greenland]] and [[Sable Island]] off [[North America]]; [[Barbados]] and [[Trinidad]] off [[South America]]; [[Great Britain]], [[Ireland]] and [[Sicily]] off [[Europe]]; [[Sumatra]] and [[Java]] off [[Asia]]; and [[New Guinea]] and [[Tasmania]] off [[Australia]].
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A special type of continental island is the '''microcontinental island''', which results when a continent is [[rift (geology)|rift]]ed. Examples are [[Madagascar]] off [[Africa]]; the [[Kerguelen Islands]]; and some of the [[Seychelles]]. Another subtype is an island or [[shoal|bar]] formed by deposition of sediment where a water current loses some of its carrying capacity. An example is [[barrier island]]s, which are accumulations of [[sand]] deposited by sea currents on the continental shelf. Another example is islands in [[river delta]]s or in large rivers. While some are transitory and may disappear if the volume or speed of the current changes, others are stable and long-lived.
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    Recent Continental Islands are always surrounded by a shallow sea (almost always less than 100 fathoms deep), so that they are connected with the continent by a submarine bank, and an elevation of 600 feet would again join them to it. They are generally situated near to continents, but sometimes at a distance of several [[p. 5]] hundred miles, as in the case of Borneo, about 600 miles from Cambodia, the intervening sea being everywhere less than 100 fathoms deep.
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    Ancient Continental Islands are always separated from the adjacent continent by a deep sea, though they are usually no further off than the more recent islands. Thus, Madagascar is separated from Africa by a strait which is about 2,000 fathoms deep, and there is more than 1,000 fathoms between Hayti and the coast of South America.
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    Oceanic Islands are usually situated in mid-ocean and surrounded by very deep seas, examples of which are the Azores, St. Helena, and the Sandwich Islands. But there are some exceptions. Thus, the Cape de Verde Islands, the Canaries, and Madeira, are all within 400 miles of the coast of Africa, while some of the Canary Islands are only 50 miles distant from it; but even these are separated from the mainland by a depth of more than 1,000 fathoms.
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==Types==
 
=== Continental islands ===<!-- This section is linked from [[Great Barrier Reef]] —>
 
 
[[Image:Angelskyview.jpg|thumb|left|[[Angel Island, California|Angel Island]] in the San Francisco Bay]]
 
[[Image:Angelskyview.jpg|thumb|left|[[Angel Island, California|Angel Island]] in the San Francisco Bay]]
Continental islands are bodies of land that lie on the [[continental shelf]] of a continent. Examples include [[Greenland]] and [[Sable Island]] off [[North America]]; [[Barbados]] and [[Trinidad]] off [[South America]]; [[Great Britain]], [[Ireland]] and [[Sicily]] off [[Europe]]; [[Sumatra]] and [[Java (island)|Java]] off [[Asia]]; and [[New Guinea]] and [[Tasmania]] off [[Australia]].
 
  
A special type of continental island is the '''microcontinental island''', which results when a continent is [[rift (geology)|rift]]ed. Examples are [[Madagascar]] off [[Africa]]; the [[Kerguelen Islands]]; and some of the [[Seychelles]].
 
 
Another subtype is an island or [[shoal|bar]] formed by deposition of sediment where a water current loses some of its carrying capacity. An example is [[barrier island]]s, which are accumulations of [[sand]] deposited by sea currents on the continental shelf. Another example is islands in [[river delta]]s or in large rivers. While some are transitory and may disappear if the volume or speed of the current changes, others are stable and long-lived.
 
  
 
=== Oceanic islands ===
 
=== Oceanic islands ===
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*  Human activity
 
*  Human activity
  
== See also ==
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{{commons|Island}}
 
*[[Desert island]]
 
*[[Insularity]]
 
*[[Island biogeography]]
 
*[[Island country]]
 
*[[Islescape]]
 
*[[Islomania]]
 
*[[List of artificial islands]]
 
*[[List of divided islands]]
 
*[[List of fictional islands]]
 
*[[List of islands]]
 
*[[List of islands by area]]
 
*[[List of islands by name]]
 
*[[List of islands by highest point]]
 
*[[List of islands by population]]
 
*[[Phantom island]]
 
*[[Private island]]
 
*[[Reef]]
 
*[[Skerry]]
 
*[[Small islands]]
 
*[[Tidal island]]
 
  
 
==Notes==
 
==Notes==

Revision as of 04:48, 20 April 2008


Mokuaeae Island, off Kilauea Point, Kauai, Hawaii.


An island or isle is any piece of land that is completely surrounded by water, above high tide, and isolated from other significant landmasses. Very small islands such as emergent land features on atolls are called islets. A key or cay is another name for a small island or islet. An island in a river or lake may be called an eyot, IPA [aɪət]. There are two main types of islands: continental islands and oceanic islands. There are also artificial islands. A grouping of geographically and/or geologically related islands is called an archipelago.

The word island comes from Old English ī(e)gland (literally, "watery land"). However, the spelling of the word was modified in the 15th century by association with the etymologically unrelated Old French loanword isle.[1]

Definition

A small Fijian island.
File:Island.jpg
A small island in the Adriatic Sea
File:Manhattan.jpg
Manhattan Island, New York. One of the world's most densely populated islands at 67,000 residents per square mile.

An island is any area of land which is smaller than a continent and is entirely surrounded by water and my occur in oceans, seas, lakes, or rivers. Islands closely grouped together are called an archipelago.

There is no standard of size which distinguishes islands from islets and continents. Any landmass surrounded by water could be considered an island. Under this terminology all the land masses on the planet could be considered islands.

Often when defining islands as pieces of land that are completely surrounded by water, narrow bodies of water like rivers and canals are generally left out of consideration. For instance, in France the Canal du Midi connects the Garonne river to the Mediterranean Sea, thereby completing a continuous water connection from the Atlantic Ocean to the Mediterranean Sea. So technically, the land mass that includes the Iberian Peninsula and the part of France that is south of the Garonne River and the Canal du Midi is completely surrounded by water. For a completely natural example, the Orinoco River splits into two branches near Tamatama, in Amazonas state, Venezuela. The southern branch flows south and joins the Rio Negro, and then the Amazon. Thus, all of the Guianas (Guyana, Suriname, and French Guiana) and substantial parts of Brazil and Venezuela are surrounded by (river or ocean) water. These instances are not generally considered islands.

This also helps explain why Africa-Eurasia can be seen as one continuous landmass (and thus technically the biggest island): generally the Suez Canal is not seen as something that divides the land mass in two.

On the other hand, an island may still be described as such despite the presence of a land bridge, such as Singapore and its causeway or the various Dutch delta Islands, such as IJsselmonde. The retaining of the island description may therefore be to some degree simply due to historical reasons - though the land bridges are often of a different geological nature (for example sand instead of stone), and thus the islands remain islands in a more scientific sense as well.

Types of islands

It is generally accepted that there are two types of islands: Oceanic and Continental. Continental Islands are thought to have been connected to the nearby continent at some point in time, and separated either recently (in a geologic frame of reference) or in ancient eras. Oceanic Islands are those which were never connected to another body of land but formed in mid-ocean. However, some schools of thought break this into a further categorization, including Recent Continental Islands, Ancient Continental Islands and Oceanic Islands.

With the exception of the Seychelles Islands in the Indian Ocean, Oceanic Islands are always either coralline or volcanic in composition. The geological make-up of Continental Islands resembles that of continents with a variety of formations, most often comprised of varying ages of stratifed rock.


HERE

Continental islands

Continental islands are bodies of land that lie on the continental shelf of a continent. Examples include Greenland and Sable Island off North America; Barbados and Trinidad off South America; Great Britain, Ireland and Sicily off Europe; Sumatra and Java off Asia; and New Guinea and Tasmania off Australia.

A special type of continental island is the microcontinental island, which results when a continent is rifted. Examples are Madagascar off Africa; the Kerguelen Islands; and some of the Seychelles. Another subtype is an island or bar formed by deposition of sediment where a water current loses some of its carrying capacity. An example is barrier islands, which are accumulations of sand deposited by sea currents on the continental shelf. Another example is islands in river deltas or in large rivers. While some are transitory and may disappear if the volume or speed of the current changes, others are stable and long-lived.




   Recent Continental Islands are always surrounded by a shallow sea (almost always less than 100 fathoms deep), so that they are connected with the continent by a submarine bank, and an elevation of 600 feet would again join them to it. They are generally situated near to continents, but sometimes at a distance of several p. 5 hundred miles, as in the case of Borneo, about 600 miles from Cambodia, the intervening sea being everywhere less than 100 fathoms deep. 
   Ancient Continental Islands are always separated from the adjacent continent by a deep sea, though they are usually no further off than the more recent islands. Thus, Madagascar is separated from Africa by a strait which is about 2,000 fathoms deep, and there is more than 1,000 fathoms between Hayti and the coast of South America. 
   Oceanic Islands are usually situated in mid-ocean and surrounded by very deep seas, examples of which are the Azores, St. Helena, and the Sandwich Islands. But there are some exceptions. Thus, the Cape de Verde Islands, the Canaries, and Madeira, are all within 400 miles of the coast of Africa, while some of the Canary Islands are only 50 miles distant from it; but even these are separated from the mainland by a depth of more than 1,000 fathoms. 


File:Angelskyview.jpg
Angel Island in the San Francisco Bay


Oceanic islands

The islands of Hawai'i are volcanic islands.
Wake Island is a volcanic island that has become an atoll.

Oceanic islands are ones that do not sit on continental shelves. They are volcanic in origin. One type of 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 include the Mariana Islands, the Aleutian Islands, Republic of Mauritius and most of Tonga in the Pacific Ocean. Some of the Lesser Antilles and the South Sandwich Islands are the only Atlantic Ocean examples.

Another type of oceanic island occurs where an oceanic rift reaches the surface. There are two examples: Iceland, which is the world's largest volcanic island, and Jan Mayen—both are in the Atlantic.

A third type of 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 eroded down and "drowned" by isostatic adjustment, becoming a seamount. 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 then extends 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. Another hot spot in the Atlantic is the island of Surtsey, which was formed in 1963.

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 include the Maldives in the Indian Ocean and Line Islands in the Pacific.

Phantom islands

The Zeno map of 1558 showing Frisland – a phantom island in the North Atlantic

Phantom islands are islands that were believed to exist, and appeared on maps for a period of time (sometimes centuries) during recorded history, but were later removed after they proved nonexistent. In contrast, lost lands are islands or continents believed by some to have existed during prehistory, often associated with ancient myths and legends.

Phantom islands usually stem from the reports of early sailors exploring new realms. Some arose through the mislocation of actual islands, or other errors in geography. For instance, Pepys Island was actually a misidentification of the Falkland Islands. The Baja California peninsula appears on some early maps as an island but was later discovered to be attached to the mainland of North America. Thule was perhaps actually discovered in the 4th century B.C.E. but was lost, and then later reidentified by ancient explorers and geographers as Shetland, Iceland, Scandinavia, or even as nonexistent.

Other phantom islands are probably due to navigational errors, the misidentification of icebergs, fog banks, or to optical illusions.

While many phantom islands appear never to have existed, a few (such as, perhaps, Thompson Island) may have been actual islands subsequently destroyed by volcanic explosions, earthquakes or submarine landslides, or low-lying lands such as sand banks that are no longer above water.


Island biogeography

The theory of island biogeography holds that the number of species found on an island (the equilibrium number) is determined by two factors, the effect of distance from the mainland and the effect of island size. These would affect the rate of extinction on the islands and the level of immigration.

Islands closer to the mainland are more likely to receive immigrants from the mainland than those farther away from the mainland. The equilibrium number of an island close to Africa is going to be larger than that of one found in the mid-Atlantic. This is the distance effect. The size effect reflects a long known relationship between island size and species diversity. On smaller islands the chance of extinction is greater than on larger ones. Thus larger islands can hold more species than smaller ones. The play between these two factors can be used to establish how many species an island can hold at equilibrium.

The theory of island biogeography was tested by Wilson and his student Daniel Simberloff in the mangroves off Florida. Small islands of mangroves were surveyed then fumigated with methyl bromide to clear their insect and arthropod communities. The islands were then monitored to study the immigration of species to the islands (the experimental equivalent of the creation of new islands). Within a year the islands had been recolonized, and had reached equilibrium, with islands closer to the mainland having more species, as predicted.

Research conducted at the rainforest research station on Barro Colorado Island has yielded a large number of publications concerning the ecological changes following the formation of islands, such as the local extinction of large predators and the subsequent changes in prey populations.


Factors that Influence Island Communities

  • Degree of isolation (distance to nearest neighbor, and mainland)
  • Length of isolation (time)
  • Size of island (larger area usually facilitates greater diversity)
  • Climate (tropical versus arctic, humid versus arid, etc.)
  • Location relative to ocean currents (influences nutrient, fish, bird, and seed flow patterns)
  • Initial plant and animal composition if previously attached to a larger land mass (e.g., marsupials, primates, etc.)
  • The species composition of earliest arrivals (if always isolated)
  • Serendipity (the impacts of chance arrivals)
  • Human activity


Notes

  1. Island. Dictionary.com. Retrieved October 6, 2007.

References
ISBN links support NWE through referral fees

Print sources
  • Firestone, Clark Barnaby. 1924. The Coasts of Illusion: A Study of Travel Tales, Harper Books.
  • Gaddis, Vincent. 1965. Invisible Horizons, Chilton Books. New York.
  • Larson, Edward J. 2001. Evolution's workshop: God and science on the Galápagos Islands. New York: Basic Books. ISBN 0465038107
  • MacArthur, R. H. and Wilson, E. O. 1967. The Theory of Island Biogeography. Princeton, N.J.: Princeton University Press.
  • Menard, Henry W. 1986. Islands. Scientific American Library series, no. 17. New York: Scientific American Library. ISBN 0716750171
  • Newmark, W. D., A land-bridge island perspective on mammalian extinctions in western North American parks, Nature, 325, 430 - 432 (29 January 1987)
  • Nunn, Patrick D. 1994. Oceanic islands. The Natural environment. Oxford, UK: Blackwell. ISBN 0631178112
  • Pilkey, Orrin H., and Mary Edna Fraser. 2003. A celebration of the world's Barrier islands. New York: Columbia University Press. ISBN 9780231119702
  • Quammen, David. 1997. The Song of the Dodo: Island Biogeography in an Age of Extinctions. Scribner. ISBN 0684827123
  • Stommel, Henry. 1984. Lost Islands: The Story of Islands That Have Vanished from Nautical Charts, University of British Columbia Press. ISBN 0774802103
  • Allan A. Schoenherr, C. Robert Feldmeth, Michael J. Emerson. 2003. Natural History of the Islands of California. University of California Press.
Online sources

External links

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Wikisource has an original article from the 1911 Encyclopædia Britannica about:
Island

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