Atoll Lesson for Kids: Definition, Formation & Facts

Instructor: Jennifer Farrell

Jen has taught Science in accredited schools in North & South America for thirteen years and has a degree in Sociology (Epidemiology & Aids Research).

Need a tropical vacation? Take an adventure to a special type of remote island called an atoll. In this lesson, we will investigate what is an atoll, how does an atoll form, and some interesting facts.

What is an Atoll?

Have you ever closed your eyes and dreamt you were relaxing on a tropical island, surrounded by a stunning turquoise sea? You may have unknowingly been daydreaming of an atoll. An atoll is a coral reef island shaped like a doughnut. The coral surrounds a lagoon. A lagoon is an area of shallow sea that is separated from the open ocean by a reef. Atolls can be made up of several small islands, which are called islets, and they may also have a larger central island.

Grab your passport and bags; we are diving in!

An atoll has a doughnut shape and is made out of coral.

Atoll Formation

To understand the process involved in the formation of these picture-perfect islands, we will divide what would normally take 30 million years into three main stages:

  1. Underwater volcanoes erupt, and lava builds up on the sea floor. Over time, this creates underwater mountains and eventually islands. The underwater mountains are called seamounts.
  2. A coral reef forms around the island just below the surface of the water.
  3. Erosion from the natural forces of water and wind wear away the volcanic island. Over the course of millions of years:
  • the island shrinks deep into the sea.
  • over time, the coral changes into tiny pieces of sand.
  • the sand forms a doughnut-shaped island.
  • eventually, the coral also begins to erode.

The image below shows the steps of how an atoll forms. The pink and purple around the island represent coral.

Formation of an atoll.
atoll formation

Scientific Research on Formation

Scientists have been researching atolls since Charles Darwin explored the seas in the mid-1800s. To this day, scientists are fascinated by the erosion of the coral reef once an atoll is already formed. Some scientists believe the temperature of the ocean is the number one factor causing the coral reef's erosion around an atoll, while others think the waves and currents are the reason for eroding and reshaping atolls. It is hard to figure out the reason since most atolls are situated in faraway regions that are difficult to reach.

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