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 atolls can be called islets, skerries, cays or keys. An isla ...
of
volcanic
A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.
On Earth, volcanoes are most often found where tectonic plat ...
origin. The term can be used to distinguish such islands from
low island
Geologically, a low island is an island of coral origin. The term applies whether the island was formed as a result of sedimentation upon a coral reef or of the uplifting of such islands. The term is used to distinguish such islands from h ...
s, which are formed from
sedimentation or the
uplifting of
coral reef
A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of Colony (biology), colonies of coral polyp (zoology), polyps held together by calcium carbonate. Most coral reefs are built from stony corals, wh ...
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 surface level of one or more among Earth's coastal bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical datuma standardis ...
, often classified as "
islets or rocks", while some low islands, such as
Banaba
BanabaThe correct spelling and etymology in Gilbertese should be ''Bwanaba'' but the Constitution of Kiribati writes Banaba. Because of the spelling in English or French, the name was very often written Paanapa or Paanopa, as it was in 1901 Ac ...
,
Henderson Island,
Makatea,
Nauru, and
Niue
Niue (, ; niu, Niuē) is an island country in the South Pacific Ocean, northeast of New Zealand. Niue's land area is about and its population, predominantly Polynesian, was about 1,600 in 2016. Niue is located in a triangle between T ...
, as uplifted
coral islands, 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 dire ...
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 present beneath Earth's surface in rock and Pore space in soil, soil pore spaces and in the fractures of stratum, rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit ...
, while low islands often do not, so high islands are more likely to be habitable.
See also
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References
External links
''Micronesian culture: High island and low island cultures'' at Britannica.com.Retrieved 2011-09-22.
{{DEFAULTSORT:High Island
Islands by type