| − | An '''atoll''' is a circular ring of [[coral]] that encloses a shallow pool, it is normaly covered by a thin layer of soil. Generally, only [[tropical plant]]s, like [[palm tree]]s, can thrive on an atoll. In many cases, atolls are built up on the [[crater]] of a [[volcano]] that has sunk below the sea. On the side of the atoll that the wind usually blows against, there is a break in the circle so the pool has an opening into the surrounding sea. | + | An '''atoll''' is a circular ring of [[coral]] that encloses a shallow pool, it is normaly covered by a thin layer of soil. Generally, only [[tropical plant]]s, like [[palm tree]]s, can thrive on an atoll. In many cases, atolls are built up on the [[crater]] of a [[volcano]] that has sunk below the sea. On the side of the atoll that the wind usually blows against, there is a break in the circle so the pool has an opening into the surrounding sea. |