A circular coral reef could indicate the earlier existence of what?

• Correct Answer: volcano
• tsunami
• landslide
• avalanche

Explanation: Reefs can form interesting shapes in the oceans. Remember that there are many volcanoes in the ocean. Coral reefs can form on volcanoes in tropical water. Since the volcanoes are cones, the reef forms in a circle around the volcano. Eventually the volcano becomes inactive. The mountain subsides and erodes so that it is below sea level. This leaves a circular coral reef ( Figure below ).

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