Types of Reefs
Geography: Cambridge International GCSE (2027 Exams), topic 2.5.2
Types of Coral Reef
There are three types of coral reef: fringing, barrier and atoll reefs.
Fringing reefs
- These grow from a shore/coastline or are adjacent to (next to) one.
- They are very sensitive to human activity.
- The Bahamas has one of the world’s most extensive coral reef systems with lots of fringing reefs.
Barrier reefs
- Barrier reefs are linear reefs (generally parallel to a shore).
- They are separated from the shore by a lagoon
- The Great Barrier Reef in Queensland, North East Australia is the world’s largest coral reef system and an example of a barrier reef.
- Barrier reefs are sensitive to human activity
Atoll reefs
- Atoll reefs are often circular.
- They surround deep lagoons.
- They are found mid-ocean.
- Most of the world’s atolls are found in:
- The Pacific Ocean: for example, Funafuti. Funafuti is a small coral atoll that’s only 20 meters (66 ft) wide at the narrowest parts, and about 400 meters (1300 ft) at the widest part of the island.
- The Indian Ocean: for example, The Maldives. The Maldives is made up of about 1,200 tiny coral islands grouped into 26 atolls.
How do atoll reefs form?
- Corals start to grow around a volcanic island, which forms a fringing reef.
- The reef continues to expand over hundreds of thousands of years.
- As the reef expands, the interior island starts to subside.
- The fringing reef becomes a barrier reef.
- Eventually, the island will completely subside beneath the water.
- This leaves a ring of coral with a lagoon in the centre (atoll reef).
Test yourself on Types of Reefs
Which of these statements about barrier reefs are true?
How do atoll reefs form?