PLZ READ THIS SHORT PASSAGE An island is an area of land that is surrounded by water. Islands can be found in all bodies of water, from streams and rivers to lakes and oceans. There are two main types of islands. They are oceanic islands and continental islands.

Oceanic Islands
Oceanic islands are the tops of underwater volcanoes. An oceanic island forms when a volcano erupts deep under the ocean. This pushes the ocean floor upward into a mountain. The island is the top of that mountain. The Hawaiian Islands are examples of oceanic islands.

Atolls are another category of island in the ocean. An atoll is a ring of land around a shallow body of water called a lagoon. Atolls form when corals build a reef around the top of a volcanic island. Over time, the reef grows until it reaches the surface of the water. Then it becomes land. The volcanic island may sink, leaving a lagoon in its place. Atolls make up the country of the Marshall Islands.

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A satellite picture of the Atafu atoll in the Pacific Ocean. The water in the center is called a lagoon. Photo: NASA Johnson Space Center.

Continental Islands
Continental islands are close to the continents. They are parts of the same land that makes up the continents. One way that continental islands form is by the flooding of valleys near the coast. Once the valleys fill with seawater, the tops of nearby hills become islands. One example of a continental island is Long Island. It lies off the coast of New York State.

The islands in rivers and lakes are also continental islands. The most famous river island is probably Manhattan, part of New York City. West of Manhattan is the Hudson River. East of Manhattan is the East River. The island has a total area of 22 square miles.

The largest river island is much bigger. It is Ilha de Marajo in the Amazon River in Brazil. It is 183 miles long and 124 miles wide. The island has an area of 18,900 square miles.

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Manhattan is a famous river island. It is also an example of a continental island. Photo: Anthony Quintano, Wikimedia Commons.

Archipelagoes
An archipelago is a group of islands. The islands in archipelagoes may be oceanic or continental. Japan and the Aleutian Islands in Alaska are archipelagoes. The country of Indonesia is the largest archipelago in the world.

Island Life
The plants and animals on continental islands are usually similar to those on the continents nearby. Oceanic islands tend to be further away from other land. As a result, fewer animals usually inhabit these islands. Oceanic islands are often covered with lush plants. The seeds for these plants are carried by wind and birds. But the variety of plants is not usually great.

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