In geology

Geology

Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...

 (and sometimes in archaeology

Archaeology

Archaeology, or archeology , is the study of human society, primarily through the recovery and analysis of the material culture and environmental data that they have left behind, which includes artifacts, architecture, biofacts and cultural landscapes...

), a high island is an island

Island

An island or isle is any piece of sub-continental land that is surrounded by water. Very small islands such as emergent land features on atolls can be called islets, cays or keys. An island in a river or lake may be called an eyot , or holm...

 of volcanic origin. The term can be used to distinguish such islands from low island

Low island

A low island is, in geology , 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...

s, whose origin is due to sedimentation

Sedimentation

Sedimentation is the tendency for particles in suspension to settle out of the fluid in which they are entrained, and come to rest against a barrier. This is due to their motion through the fluid in response to the forces acting on them: these forces can be due to gravity, centrifugal acceleration...

 or uplifting

Tectonic uplift

Tectonic uplift is a geological process most often caused by plate tectonics which increases elevation. The opposite of uplift is subsidence, which results in a decrease in elevation. Uplift may be orogenic or isostatic.-Orogenic uplift:...

 of coral reef

Coral reef

Coral reefs are underwater structures made from calcium carbonate secreted by corals. Coral reefs are colonies of tiny living animals found in marine waters that contain few nutrients. Most coral reefs are built from stony corals, which in turn consist of polyps that cluster in groups. The polyps...

s.

Definition and origin

There are a number of "high islands" which rise no more than a few feet above sea level

Sea level

Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...

, often classified as "islet

Islet

An islet is a very small island.- Types :As suggested by its origin as islette, an Old French diminutive of "isle", use of the term implies small size, but little attention is given to drawing an upper limit on its applicability....

s or rocks", while some "low islands", such as Makatea

Makatea

Makatea, or Mangaia-te-vai-tamae, is a raised coral atoll in the northwestern part of the Tuamotus. It is located 79 km southwest from Rangiroa to the west of the Palliser group. It is surrounded by spectacular cliffs, rising to a plateau 80 meters above the sea level. This island is...

, Nauru

Nauru

Nauru , officially the Republic of Nauru and formerly known as Pleasant Island, is an island country in Micronesia in the South Pacific. Its nearest neighbour is Banaba Island in Kiribati, to the east. Nauru is the world's smallest republic, covering just...

, Niue

Niue

Niue , is an island country in the South Pacific Ocean. It is commonly known as the "Rock of Polynesia", and inhabitants of the island call it "the Rock" for short. Niue is northeast of New Zealand in a triangle between Tonga to the southwest, the Samoas to the northwest, and the Cook Islands to...

, Henderson

Henderson Island (Pitcairn Islands)

Henderson Island is an uninhabited raised coral atoll in the south Pacific Ocean, that in 1902 was annexed to the Pitcairn Islands colony, a South Pacific Dependent Territory of the United Kingdom. Measuring long and wide, it has an area of and is located northeast of Pitcairn Island at . The...

 and Banaba

Banaba Island

Banaba Island , an island in the Pacific Ocean, is a solitary raised coral island west of the Gilbert Island chain and 300 km east of Nauru. It is part of the Republic of Kiribati. It has an area of 6.5 km², and the highest point on the island is also the highest point in Kiribati, at 81...

, as uplifted coral islands, rise several hundred feet 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

Pacific Islands

The Pacific Islands comprise 20,000 to 30,000 islands in the Pacific Ocean. The islands are also sometimes collectively called Oceania, although Oceania is sometimes defined as also including Australasia and the Malay Archipelago....

, where low islands are found on the fringing reefs

Coral reef

Coral reefs are underwater structures made from calcium carbonate secreted by corals. Coral reefs are colonies of tiny living animals found in marine waters that contain few nutrients. Most coral reefs are built from stony corals, which in turn consist of polyps that cluster in groups. The polyps...

 that surround most high islands. Volcanic islands are normally made over a so called hotspot

Hotspot (geology)

The places known as hotspots or hot spots in geology are volcanic regions thought to be fed by underlying mantle that is anomalously hot compared with the mantle elsewhere. They may be on, near to, or far from tectonic plate boundaries. There are two hypotheses to explain them...

.

Habitability for humans

The differences in geology and topography between high and low islands mean a lot, in terms of habitability for humans. High islands above a certain size usually have ground water, while low islands often do not. This hampers or hinders human settlement on many low islands.

External links

• Micronesian culture: High island and low island cultures at Britannica.com. Retrieved 2011-09-22.