The Birth of an Atoll

Before his famous theory of evolution, naturalist Charles Darwin proposed a theory about the formation of coral reefs and atolls. An underwater volcano (called a seamount) erupts. Over time, and with additional eruptions, the seamount grows.

The seamount rises above the surface of the ocean, creating an island. The volcano goes dormant and a coral fringing reef forms around the island.

You Can Help

By limiting our use of fossil fuels, we can slow the rate of climate change, including slowing its cascading impacts, like rising sea levels. You can help protect these ecosystems by making lifestyle changes, like carpooling or riding a bicycle when possible, turning off lights when you leave a room, and voting for policies that help curb carbon emissions.

Over hundreds of thousands of years, the island gradually sinks into the ocean as it is weighed down by the heavy reef and rock. This is called “subsidence.”

As the island sinks, the corals continue to grow upward. Eventually, a wide band of water called a lagoon forms between the land and the reef, creating a barrier reef.

The extinct volcano becomes completely submerged. As the corals keep growing and break the water’s surface, they turn into sand and rubble. Now, a coral rim surrounds a central lagoon, forming an atoll. This process can take up to 30 million years.

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