How are islands formed? What are archipelagos and coral reefs?

How are islands formed? What are archipelagos and coral reefs?

Some islands are the tops of undersea volcanoes. Others are pushed up by a volcano. Islands like the British Isles are formed when a continent breaks up and a part of it is cut off by water. A chain or group of islands is called an archipelago. The world’s biggest archipelago is Indonesia, which is made up of more than 13, 000 islands!

Coral reefs are made up of the limestone bodies of tiny coral animals. They are usually round in shape, and have a lagoon in the centre.