An island is a piece of land completely surrounded by water. There are islands in every ocean and sea. Very small islands can be called islets, or cays (say keys)

There are islands in rivers and in lakes. An island in a river or an island in a lake may be called an eyot.

There are two main kinds of islands: continental and oceanic.

Continental islands

Tasmania is a continental island, high ground that rises from Australia’s continental shelf.

Tasmania is a continental island, high ground that rises from Australia’s continental shelf.

Continental islands are bodies of high ground that rise above the sea level of the continental shelf of a continent. A continental shelf is the land that extends outwards from the continent and is covered by shallow seas. Greenland and Tasmania are examples of continental islands.

Oceanic islands

Oceanic islands are not on the continental shelf. They are active or extinct volcanoes that rise above sea level from the ocean floor.

Iceland and Tonga are examples of oceanic islands. 

Watch a video here showing how a volcanic island is formed

The few oceanic islands that are not volcanic are tectonic.  This happens where plate movements have lifted up the deep ocean floor to above the surface. Macquarie Island in the Pacific is an example of an island formed by movement of tectonic plates.

Islands are the home to many rare animal species. these are proboscis monkeys on Borneo ©Getty Images

Islands are the home to many rare animal species. these are proboscis monkeys on Borneo ©Getty Images

The largest islands

The six largest islands on Earth are Greenland (it's the biggest island), New Guinea, Borneo, Madagascar, Baffin Island and Sumatra.

Go here for a map showing the location of the largest islands in the world.

http://www.worldatlas.com/aatlas/newart/locator/majorisl.htm

The island of Borneo, a continental island, is shared by two nations: Malaysia and Indonesia

The island of Borneo, a continental island, is shared by two nations: Malaysia and Indonesia

This lemur is one of many sepcies of lemur that live on Madagascar © kidcyber image

This lemur is one of many sepcies of lemur that live on Madagascar © kidcyber image

Because islands are cut off from other landmasses, they are often the home of unique plants and animals. Borneo for example, has hundreds of plants and animals that are found nowhere else on Earth. Proboscis monkeys are found only on the island of Borneo

Read about proboscis monkeys on kidcyber

http://kidcyber.com.au/topics/animals/proboscis-monkey/

 

On Madagascar, lemurs are a unique type of monkey. More than 100 species live in forest on the island.

Read about lemurs on kidcyber here.

 http://kidcyber.com.au/topics/animals/lemurs/

A large reef and lagoon in the Maldives. iStock

A large reef and lagoon in the Maldives. iStock

Indonesia is an archipeligo made up of thousands of islands iStock

Indonesia is an archipeligo made up of thousands of islands iStock

Other kinds of islands:

  • An atoll is a ring shaped island made out of coral that has a lagoon of water inside it.
  • An atoll needs coral reef building so they are found mainly in tropical waters.  Most are in the Pacific and Indian Oceans. Atolls can be quite small or be large like Kwajalein in the Marshal Islands. It is 130 kilometres long and 32 kilometres wide.
  • The reef and lagoon area in some of the atolls of the Maldives are larger than 3000 square kilometres. 
There are thousands of desert islands in the oceans.

There are thousands of desert islands in the oceans.

  • An archipelago is a group of islands in the same part of the sea. Indonesia and the Philippines are archipelagos.

  • A desert island is one where no one lives. Coral Sea Islands off the northeastern coast of Australia are an example of desert islands.