an island or isle is a piece of subcontinental land completely surrounded by water.very small islands such as emergent land features on atolls can be called islets, skerries, cays or keys.an island in a river or a lake island may be called an eyot or ait, and a small island off the coast may be called a holm.sedimentary islands in the ganges delta are called chars.a grouping of geographically or geologically related islands, such as the philippines, is referred to as an archipelago.there are two main types of islands in the sea: continental islands and oceanic islands.there are also artificial islands (man-made islands).there are about 900,000 official islands in the world.this number consists of all the officially-reported islands of each country.the total number of islands in the world is unknown.there may be hundreds of thousands of tiny islands that are unknown and uncounted.the number of sea islands in the world is estimated to be more than 200,000.the total area of the world's sea islands is approx.9,963,000 sq km, which is similar to the area of canada and accounts for roughly 1/15 (or 6.7%) of the total land area of earth.dutch eiland ('island'), german eiland ('small island')).however, the spelling of the word was modified in the 15th century because of a false etymology caused by an incorrect association with the etymologically unrelated old french loanword isle, which itself comes from the latin word insula.old english ieg is actually a cognate of swedish ö and german aue, and related to latin aqua (water).continents are often considered to be the largest landmass of a particular continental plate; this holds true for australia, which sits on its own continental lithosphere and tectonic plate (the australian plate).by contrast, islands are usually seen as being extensions of the oceanic crust (e.g.volcanic islands), or as belonging to a continental plate containing a larger landmass (continental islands); the latter is the case of greenland, which sits on the north american plate.examples are borneo, java, sumatra, sakhalin, taiwan and hainan off asia; new guinea, tasmania, and kangaroo island off australia; great britain, ireland, and sicily off europe; greenland, newfoundland, long island, and sable island off north america; and barbados, the falkland islands, and trinidad off south america.examples are madagascar and socotra off africa, new caledonia, new zealand, and some of the seychelles.if this island has a seashore as well as being encircled by two river systems, it becomes what might be called a subcontinental island.the one formed by wollaston lake is very large, about 2,000,000 km2 (770,000 sq mi).this includes:  barrier islands, which are accumulations of sand deposited by sea currents on the continental shelves fluvial or alluvial islands formed in river deltas or midstream within large rivers.while some are transitory and may disappear if the volume or speed of the current changes, others are stable and long-lived.other definitions limit the term to only refer to islands with no past geological connections to a continental landmass.the vast majority are volcanic in origin, such as saint helena in the south atlantic ocean.the few oceanic islands that are not volcanic are tectonic in origin and arise where plate movements have lifted up the ocean floor above the surface.examples are the saint peter and saint paul archipelago in the north atlantic ocean and macquarie island in the south pacific ocean.these islands arise from volcanoes where the subduction of one plate under another is occurring.examples are the aleutian islands, the mariana islands, and most of tonga in the pacific ocean.
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