What is the difference between an island and an atoll?

Answer 1

An atoll is formed from an island, but it isn't entirely an island. It's a coral reef that makes the different. The reef grows in a ring around the island and the island erodes, until little if any of it is above the surface of the water and the coral reef remains.

Islands are any small body of land surrounded by water. Islands in the middle of the ocean are usually volcanic and islands in lakes and near continents are usually just areas of the continental shelf surrounding the continent with a higher elevation.

To actually answer your question, the KEY difference is the reef.

Answer 2

They are both related to volcanic activity. In the case of the Hawaiian island chain this is caused by a mantle hotspot leading to significant volcanism creating the volcanoes that form the island chain. In the case of an atoll these form around older extinct oceanic volcanoes which are subsiding. The coral forms in a fringing ring in the shallows around the volcano and as it continues to subside, the coral continues to grow upwards until eventually the volcano subsides or is eroded to a depth below the surface leaving the ring of coral with a shallow lagoon in the centre known as an atoll.

Answer 3

An atoll has a lagoon in the middle and Hawaii does not.

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