Coral Atolls

An atoll is a very special kind of island. It is shaped like a ring. In the middle is a pool of calm water called a lagoon. Atolls are made from coral, which is built by tiny sea animals.

How Atolls Form

Atolls start with a volcano in the ocean. Coral grows around the edges of the volcano's island. Over a long time, the volcano sinks back into the sea. But the coral keeps growing, leaving a ring of land behind.

An old drawing shows how coral atolls are shaped.
An old drawing shows how coral atolls are shaped. (Darwin, Charles; Williams, Joseph W. / Wikimedia Commons)

Homes for Sea Life

Atolls are full of life. The lagoons are safe homes for many fish, turtles, and sharks. Colorful coral reefs grow around them. Sea birds also nest on the sandy parts of the islands.

Fun Facts

  • Most atolls are found in the Pacific and Indian Oceans.
  • The idea of how atolls form was first explained by Charles Darwin.
  • Some people live on atolls, even though there is not much land.

Did You Know?

Kiritimati, also called Christmas Island, is one of the largest coral atolls in the world.