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This animation shows the dynamic process of how a coral atoll forms. Corals (represented in tan and purple) begin to settle and grow around an oceanic island forming a fringing reef. It can take as long as 10,000 years for a fringing reef to form. Over the next 100,000 years, if conditions are favorable, the reef will continue to expand. As the reef expands, the interior island usually begins to subside and the fringing reef turns into a barrier reef. When the island completely subsides beneath the water, it leaves a ring of growing coral with an open lagoon in its center, this is called an atoll. The process of atoll formation may take as long as 30 million years to occur. Research continues into how coral atolls form. Figure credit: NOAA
View a video animation in YouTube that explains how the Hawaiian archipelago formed.
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