Components of archipelagoes are made up of islands. An archipelago is a group of islands, islets, and reefs that are close together and form a chain or cluster. Islands are land masses that are surrounded by water and are usually smaller than continents. They can be formed by volcanic activity, erosion, or the rising of sea levels. Islands can also be man-made, such as those created by the building of dams. Islands can provide habitats for many species of plants and animals, and can be home to unique cultures and societies.