What is the key feature of a coral atoll?
The key feature of a coral atoll is that its central island is separated from the outer reef by a deep lagoon (b). Coral atolls are ring-shaped coral reefs that form around a central lagoon. The central island of a coral atoll is usually made up of coral debris and sand, and it is surrounded by a protective barrier reef. This barrier reef creates a deep lagoon between the central island and the outer reef. The lagoon is often shallow near the central island, gradually deepening towards the outer reef.
Characteristics of Coral Atolls
Coral Atolls Formation: Coral atolls are formed from the accumulation of coral debris and sand on the top of submerged volcanoes or oceanic islands. Over time, coral polyps build up reefs that encircle a central lagoon, creating the ring-like structure of a coral atoll.
Central Island Composition:
The central island of a coral atoll is typically low-lying and composed of coral debris, beach rock, and sand. It may support vegetation and sometimes human settlements. The presence of a central island is what distinguishes coral atolls from other types of coral reefs.
Barrier Reef and Deep Lagoon:
The protective barrier reef that surrounds the central island of a coral atoll creates a deep lagoon between the central island and the outer rim of the reef. This separation by a deep lagoon is a unique characteristic of coral atolls that sets them apart from other types of islands.
Comparison with Volcanic Islands:
While coral atolls can form over volcanic islands, the key feature that differentiates them from volcanic islands is the presence of the deep lagoon that separates the central island from the outer reef. Volcanic islands are typically formed by volcanic activity and do not have the same ring-like structure as coral atolls.
In summary, the key feature of a coral atoll is the presence of a central island that is separated from the outer reef by a deep lagoon. This characteristic distinguishes coral atolls from other types of islands and is essential to their formation and ecological diversity.