Island

An island is an area of land surrounded by water. It can occur in an ocean, a sea, a lake, or a river. Islands have different origins. Some form when volcanic activity brings rock and other materials above the water’s surface. Others are pieces of continents separated by a rise in sea level or by movements of Earth’s crust.

Some islands are also made mainly of sediment, especially in rivers and near coasts. Their size ranges from tiny islets to very large landmasses such as Greenland, which is generally regarded as the world’s largest island. An island environment depends on its climate, geology, and location.

A tropical island may have coral reefs, mangroves, and vegetation adapted to warm conditions, while an island at high latitudes may have rocky or glacial landscapes. Isolation can sometimes lead to species found nowhere else, especially when populations remain separated for long periods.

Islands are also exposed to changes in sea level, storms, and coastal erosion. Some are densely populated and heavily developed, whereas others remain almost uninhabited. They therefore form highly diverse environments in which geology, climate, and living organisms interact in distinctive ways.