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Related to atoll: Midway Atoll
An atoll is created as a coral reef builds up around an eroding volcanic island.
a·toll(ăt′ôl′, -ŏl′, ā′tôl′, ā′tŏl′)
An island or chain of islets connected by a coral reef that nearly or entirely encloses a lagoon.
(Physical Geography) a circular coral reef or string of coral islands surrounding a lagoon
[C17: from atollon, native name in the Maldive Islands]
at•oll(ˈæt ɔl, -ɒl, -oʊl)
a ring-shaped coral reef or a string of closely spaced small coral islands, enclosing or nearly enclosing a shallow lagoon.
[1615–25; earlier atollon < French]
An atoll develops (from left to right) when a volcanic island erodes and a ring of coral grows up around it. The depression left by the crater of an eroding volcano fills with water, forming a lagoon.
A coral island forming a ring that nearly or entirely encloses a shallow lagoon.
A ring-shaped coral reef enclosing a lagoon.