Which type of reef forms very closel to the shoreline of a volcanic island

They are called fringing reefs. They grow directly from shore and form borders along the shoreline. When a fringing reef continues to grow upward from a volcanic island that has sunk entirely below the sea level, an atoll is formed. Atolls are usually circular or oval in shape, with an open lagoon in the center. The fringing reef is the most common type of coral reef. They however tend to be very sensitive to human induced pollution in the water and are easily destroyed by such.

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