How do coralline islands are formed?

Coralline islands, also known as coral atolls, are formed through a process that begins with the growth of coral reefs around a volcanic island. Over time, as the volcano erodes and sinks, the coral continues to grow upwards, maintaining its structure above sea level. Eventually, the volcanic island may completely submerge, leaving a ring of coral and a lagoon in the center, characteristic of atoll formation. The continuous deposition of calcium carbonate from corals and other marine organisms contributes to the island's stability and expansion.