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The Formation of an Atoll

Amita Vadlamudi

A computer systems engineer by profession, Amita Vadlamudi appreciates Earth’s natural wonders as well. Amita Vadlamudi enjoys learning about landforms and marine biology.

An atoll is a unique ringed landform that forms over millions of years. It begins as an undersea volcano known as a seamount. As the volcano erupts and lava hardens under the water, the elevation of the seamount increases until it breaches the surface of the ocean and becomes an island.

After the volcano goes dormant, corals colonize the rock formation just below the water’s surface to create a fringe reef. Between the reef and the island is a shallow border of water called a lagoon. The volcanic island eventually the roads and sinks below the water’s surface, becoming a flat structure known as a guyot.
The guyot continues to sink into the ocean floor, but the coral reef remains as a barrier reef. The ocean-facing coral thrives while the coral on the inside of the lagoon dies off and causes the lagoon water to turn bright turquoise. The ocean erodes the dead coral into sand, which builds up on the ring-shaped reef. Seeds and other organic matter can also wash up on the reef with the sand to sustain life on the new, ringed island, now known as an atoll.

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