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Why do many coral sand cays form on the sheltered side of a reef?
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coral reef
The Great Barrier Reef, off the coast of Queensland, Australia, is the world's largest coral reef.
Coral sand cays typically form on the sheltered, leeward side of a coral reef because of the way sediment is transported and deposited across the reef platform.12
The process occurs as follows:
- Sediment Transport: Debris and sediment are broken off from the reef, particularly from the windward slopes, and are carried across the reef platform by waves and tidal currents.12
- Deposition: As this material is transported toward the leeward side, it reaches areas where the water velocity is reduced abruptly. This loss of energy causes the sediment to settle and accumulate.2
- Wave Dynamics: The accumulation is further supported by the refraction and convergence of waves around the platform, which prevents the deposited sand from washing over the edge of the reef.1
Once these deposits accumulate, they may be stabilized by the formation of beach rock—created through the cementation of grains—and the eventual growth of vegetation.12