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 ...
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 ...
origin. The term can be used to distinguish such islands from low island
Geologically, a low island is an island
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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 ...
s (which have often formed on sunken volcanos).
Definition and origin
There are a number of "high islands" that rise no more than abovesea 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 ...
, 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 ( ...
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 ...
, 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
...
, 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 ...
, and Niue
Niue ( or ; niu, Niuē) 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 ...
, 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 freshgroundwater
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 ...
, 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