Islands

Islands 

tracts of land entirely surrounded by the waters of oceans, seas, lakes, or rivers. Islands differ from continents in that they are relatively small. They occur individually or in groups called archipelagoes.

The islands of oceans and seas are subdivided into continental islands, islands of the transitional zone, and oceanic islands. Continental islands, which rise above sea level from the underwater rim of the continents, include some of the world’s largest islands—Greenland, Kalimantan (Borneo), and Madagascar. They are usually composed of bedrock, although smaller islands may be formed through the accumulation of sediment by the action of waves and tides. Most of the islands of the transitional zones are volcanic; in some areas, however, there are mud volcano islands (for example, in the southern part of the Caspian Sea) and coral islands. Oceanic islands rise up from the ocean floor and mid-ocean ridges, and most are volcanic or coral islands.

The isolation of islands from continents determines the characteristics of their natural features, particularly their fauna and flora. Islands have fewer species than nearby continental areas lying in the same natural zone, and they have a high percentage of endemic species. This is especially true of oceanic islands.

The islands of rivers and lakes are divided into alluvial and erosion islands. The former are created through the accumulation of sediments in a channel or near the shore of a lake, and the latter are formed when river channels flow around an outlier composed of bedrock and alluvium or when a protruding segment

Table 1. The world’s largest archipelagoes and islands
			Area (sq km)
1Partly in the Pacific Ocean 2Partly in the Atlantic Ocean
	Pacific Ocean
Greater Sunda			1,485,000
Kalimantan (Borneo)			735,000
Sumatra			435,000
Sulawesi (Celebes)			179,400
New Guinea			809,000
Japan			372,200
Honshu		approx.	228,000
Hokkaido		approx.	78,000
Philippines		approx.	300,000
Luzon			105,600
Mindanao			94,600
New Zealand			268,700
South Island			150,500
North Island			115,000
Lesser Sunda			128,000
Molucca			83,700
Sakhalin			76,400
Tasmania		approx	68,000
Taiwan		approx.	36,000
Hainan	Atlantic Ocean		34,000
British Isles		approx	325,000
Great Britain			218,000
Ireland			84,000
Greater Antilles			209,000
Cuba			105,000
Hispaniola		approx.	77,000
Newfoundland			112,300
Tierra del Fuego1	Indian Ocean	approx	72,000
Madagascar			590,000
Sri Lanka (Ceylon)	Arctic Ocean		65,600
Greenland2			2,176,000
Canadian Arctic Archipelago2			1,300,000
Baffin			478,000
Victoria			221,000
Ellesmere			212,700
Iceland		approx	103,000
Novaia Zemlia			83,100
Spitsbergen		approx	62,000

of land near a lake is cut off by abrasion. (See Table 1 for the area of the world’s largest islands and archipelagoes.)