The Atlantic has large stretches of open water without islands. There are no archipelagoes consisting of thousands of islands, such as those found in the Pacific. Most of the large islands, such as the British Isles, Greenland, Newfoundland, and the main islands of the Greater Antilles, were once connected with the continents.
Other islands, especially those far out at sea, were formed by successive eruptions of volcanic material far below the water's surface. Only the tops of these underwater mountains and high plateaus are exposed as islands. Examples of such islands in the North Atlantic are the Faeroe Islands, the Azores, Madeira, the Canary Islands, the Cape Verde Islands, and São Tomé. Volcanic islands of the South Atlantic include St. Helena, Ascension, the Tristan da Cunha group, and the South Sandwich Islands. In contrast to these usually high-peaked islands, Bermuda and some of the West Indies are flat coral islands.
The world's largest volcanic island is Iceland. It has many signs of continuing volcanic activity, such as hot springs, geysers, and active volcanoes. Another volcanic island, Surtsey, emerged off the coast of Iceland in 1963.