atoll: Quick Facts

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Last updated

Oct. 18, 2026

Photos

Diagram showing the stages of atoll formation: a volcanic island forms above a mantle plume, then gradually sinks to become a sinking island, guyot, barrier reef, and eventually an atoll or seamount, with cross-sections illustrating magma movement, oceanic crust, and plate tectonics.

A three-part diagram shows the formation of a coral atoll: first, a volcanic island with a surrounding coral reef; next, the island sinks as the coral reef grows upward; finally, the island disappears below the surface, leaving a ring-shaped atoll of coral with a central lagoon. Both top and side views are provided for each stage.

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Topics

coral-reef lagoon mountain glacier glacial landform valley coastal landforms Desert coral reef Grassland plateau playa