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How are atolls different from barrier reefs?
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coral reef
The Great Barrier Reef, off the coast of Queensland, Australia, is the world's largest coral reef.
The primary difference between barrier reefs and atolls lies in the presence of a central landmass.
- Barrier Reefs: These reefs form offshore, separated from a mainland or island by a lagoon or channel. They are often associated with the earlier stages of reef development where a volcanic island is still present.12
- Atolls: These are essentially circular barrier reefs that lack a central landmass. According to the subsidence theory popularized by Charles Darwin, an atoll represents the final stage of development, occurring after the original volcanic island has completely subsided below sea level, leaving only the reef rim surrounding a central lagoon.132
While both structures enclose lagoons, the barrier reef is defined by its proximity to a non-reef landmass, whereas the atoll is defined by the absence of one.12