MANY geography students may have come across the term, atoll.

But for those who didn't listen in their geography classes, the phenomenon may still be a mystery. Here we explain what an atoll actually is.

What is an atoll?

You may have come across an atoll on your travels and not actually known it.

An atoll is a ring-shaped coral reef, an island or a series of islets formed by coral.

It surrounds a body of water called a lagoon, which is a shallow body of water separated from the larger body of water.

Sites which include atolls have proved to be dangerous throughout history.

They are hidden by ocean waves and there have been wrecks of ancient Polynesian canoes and American warships because of them.

Kon-Tiki is one of the most famous shipwrecks in history, which was caused by the strong winds and currents that surround an atoll.

It was built and sailed by explorer Thor HeyerDahl and his crew in 1947.

It sailed a distance of 6,980km from Peru to the South Pacific before encountering difficulties in the region of Polynesia, just as they were about to reach the first island.

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The atoll prevented the Kon-Tiki from docking on the island and wrecked on the coral of the second, Raroia atoll.

Nearby islanders came to the rescue of the Europeans on board and rescued them from the washed-up wreck.

This is why most atolls are inhabitant islands as they are very difficult to reach.

One can find many shipwrecks from the eighteenth century to World War II at the bottom of the atoll sites.

Since they are deserted islands, they were a popular spot for the United States, Britain and France to test nuclear weapons.

How are atolls formed?

The process starts when an underwater volcano, also known as seamounts, erupts and pile up lava on the sea floor.

Eventually it breaks out from the water level and it becomes an oceanic island.

Then, corals start building a reef around the island and it becomes what's called a fringing reef.

It surrounds the island below the ocean surface that is what makes the water between the reef and the island, a lagoon.

It takes millions of years for the allot to fully form.

A process called subsidence takes place in which the volcanic island erodes and sinks.

The ocean waves make the top flat and turns it into what's called a guyot.

The fringing reef turns into a barrier reef which protects the lagoon from strong winds and waves.

Finally, the ocean waves start breaking some of the reef and create tiny grains of sand and other material.

These include organic matter such as plant seeds which form a ring-shaped island and create an atoll.

Where are there atolls in the world?

There are several atolls that can be found across the world, and despite its dangers they can be a sight of sheer beauty.

Atolls of the Maldives

The Maldives have 1,200 atolls and give those visiting an opportunity to perform some water-sporting activities.

The scenic beauty of these atolls provide a great experience of snorkelling and scuba diving.

Bikini Atoll

Remember when we said that some countries used atolls to test out nuclear weapons in?

Well Bikini Atoll was one of these atolls in which is located in the Marshall Islands.

The US used it to test out 23 nuclear devices between 1946 and 1958, at seven different sites in the atoll.

Now, it is used as a tourist attraction for scuba diving and have a look at the shipwrecks that piled on throughout the years.

Caroline Island

Caroline Island is one of the most clean and pure tropical islands in the world with one of the largest population of coconut crabs.

It is considered as a wildlife sanctuary because of its lack of pollution.

You might not have long to visit such island though, because it is expected to be completely underwater by 2025, as it stands six meters above sea.

Lighthouse Reef

It is one of the four atolls located in the western hemisphere and it is famous for the Great Blue Hole located in its centre.

It is considered as one of the best spots for scuba diving because as you go deeper, the more you can discover thanks to the clear water below.

There are stalactites and limestone formations which offer the diver views of exceptional beauty.

Funafuti

It is located between Hawaii and Australia in the capital of Tuvalu.

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It is only 20 metres wide at the narrowest sides and the widest sides reach 400 metres.

It is the second least populated country in the world, with 6,200 citizens after the Vatican City and it offers many activities around its sea life.

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