atoll
An atoll forms as a coral reef builds up around an eroding volcanic island.
The American Heritage® Science Dictionary Copyright © 2010 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
atoll
An atoll is created as a coral reef builds up around an eroding volcanic island.
The American Heritage® Dictionary of the English Language, 4th edition Copyright © 2010 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

A coral atoll.
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