Atoll - the type of flat coral island located in the ocean, consisting of a coral reef in the shape of a ring surrounding a central depression. Depression is called the lagoon may be elected part of the island, a small but distinct body of water or be connected with the sea. The name of the atoll was popularized by Charles Darwin.
Atoll arises przyrastania coral reefs around volcanic islands. Coral reef create millions of living organisms - polyps. Polyps dying leave behind the limestone skeletons of forming a compact structure. With time, due to the weight of the ring limestone island is reduced and gradually immersed in water. Ring remaining above the surface is eroded. One of its products is sand, where they can grow plants. Remains of plants form the soil and thus island grows. On the outer side of an atoll is formed by the waves shaped beach. It descends steeply to the depths. From the lagoon beaches are much wider, and mostly shallow water.
The word atoll comes from the official language of the Maldives. The fact is that just in the Maldives, you can find the largest atolls. Their presence is limited almost exclusively to the Pacific and Indian Oceans. In the Atlantic there is little atolls.