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Source: http://pubs.usgs.gov/fs/2002/fs025-02/

Caption: Coral atolls develop from reefs fringing volcanic islands. As first hypothesized by Charles Darwin, and confirmed by ocean drilling done by British scientists a century ago, reefs fringing volcanic islands build vertically to sea level, forming steepwalled barrier reefs. As a volcanic island subsides, or sinks, with time, the growing reef keeps pace with the rising water level. When the island eventually submerges, the ring-shaped reef forms an atoll with a central lagoon.

Graphic Design By Susan Mayfield and Sara Boore

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