Any area of land smaller than a continent and entirely surrounded by water. Islands may occur in oceans, seas, lakes, or rivers. A group of islands is called an archipelago. Continental islands are simply unsubmerged parts of a continental mass that are entirely surrounded by water; Greenland, the world's largest island, is of the continental type. Oceanic islands are produced by volcanic activity, when lava accumulates to enormous thickness until it finally protrudes above the ocean surface. The piles of lava that form Hawaii rise as high as 32,000 ft (9,700 m) above the ocean floor.

This entry comes from Encyclopædia Britannica Concise.
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