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Geologically, a high island or volcanic island is an
island An island (or isle) is an isolated piece of habitat that is surrounded by a dramatically different habitat, such as water. Very small islands such as emergent land features on atoll An atoll (), sometimes known as a coral atoll, i ...

island
of
volcanic A volcano is a rupture in the crust of a planetary-mass object A planet is an astronomical body orbit In physics, an orbit is the gravitationally curved trajectory of an physical body, object, such as the trajectory of a planet ar ...

volcanic
origin. The term can be used to distinguish such islands from
low island Geologically, a low island is an island upright=1.15, Great_Britain.html"_;"title="Ireland_(left)_and_Great_Britain">Ireland_(left)_and_Great_Britain_(right),_are_large_islands_of_north-west_Europe image:Small_Island_in_Lower_Saranac_Lake. ...
s, which are formed from
sedimentation Sedimentation is the deposition of sediments Sediment is a naturally occurring material that is broken down by processes of weathering Weathering is the deterioration of rocks A rock is any naturally occurring solid mass or aggreg ...
or the uplifting of
coral reef A coral reef is an underwater ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient c ...

coral reef
s (which have often formed on sunken volcanos).


Definition and origin

There are a number of "high islands" that rise no more than above
sea level Mean sea level (MSL) (often shortened to sea level) is an average In colloquial, ordinary language, an average is a single number taken as representative of a list of numbers, usually the sum of the numbers divided by how many numbers are in th ...

sea level
, often classified as "
islet An islet is a very small island An island (or isle) is an isolated piece of habitat that is surrounded by a dramatically different habitat, such as water. Very small islands such as emergent land features on atoll An atoll ( ...

islet
s or rocks", while some low islands, such as
Banaba BanabaThe correct spelling and etymology in Gilbertese Gilbertese or taetae ni Kiribati, also Kiribati (sometimes ''Kiribatese''), is an Austronesian language The Austronesian languages (, , , ) are a language family A language is a ...

Banaba
, Henderson Island,
Makatea Makatea, or Mangaia-te-vai-tamae, is a raised coral atoll A raised coral atoll or uplifted coral atoll is an atoll An atoll (), sometimes known as a coral atoll, is a ring-shaped coral reef A coral reef is an underwater ecosystem ...

Makatea
,
Nauru Nauru ( or ; na, Naoero), officially the Republic of Nauru ( na, Repubrikin Naoero) and formerly known as Pleasant Island, is an island country An island country or an island nation is a country A country is a distinct territory, t ...

Nauru
, and
Niue Niue ( or ; niu, Niu─ô) is an island country An island country or an island nation is a country A country is a distinct territory, territorial body or political entity. It is often referred to as the land of an individual's birth, r ...

Niue
, as uplifted
coral island A coral island is a type of island formed from coral detritus and associated organic material. It occurs in tropical and sub-tropical areas, typically as part of a coral reef which has grown to cover a far larger area under the sea. Ecosystem ...
s, rise over above sea level. The two types of islands are often found in proximity to each other, especially among the islands of the South Pacific Ocean, where low islands are found on the
fringing reef A fringing reef is one of the three main types of coral reef. It is distinguished from the other main types, barrier reefs and atolls, in that it has either an entirely shallow backreef zone (lagoon) or none at all. If a fringing reef grows direct ...
s that surround most high islands. Volcanic islands normally arise above a hotspot.


Habitability

High islands above a certain size usually have fresh
groundwater Groundwater is the water Water (chemical formula H2O) is an , transparent, tasteless, odorless, and , which is the main constituent of 's and the s of all known living organisms (in which it acts as a ). It is vital for all known form ...

groundwater
, while low islands often do not, so high islands are more likely to be habitable.


See also

* * * * * * *


References


External links


''Micronesian culture: High island and low island cultures'' at Britannica.com.
Retrieved 2011-09-22. {{Earth's landforms Islands by type