Množina: archipelagos

ETYM Italian arcipelago, properly, chief sea; Greek pref archi + pelagos sea.
A group of many islands in a large body of water.
Group or string of islands.
Group of islands, or an area of sea containing a group of islands. The islands of an archipelago are usually volcanic in origin, and they sometimes represent the tops of peaks in areas around continental margins flooded by the sea.
Volcanic islands are formed either when a hot spot within the Earth's mantle produces a chain of volcanoes on the surface, such as the Hawaiian Archipelago, or at a destructive plate margin (see plate tectonics) where the subduction of one plate beneath another produces an arc-shaped island group, such as the Aleutian Archipelago. Novaya Zemlya in the Arctic Ocean, the northern extension of the Ural Mountains, resulted from continental flooding.