85% of all the world’s seismic activity occurs around the Pacific plate. To grow an island chain:
- A crack opens in the sea floor
- Hot, volcanic matter comes up through the crack
- A submarine volcano grows and grows until it breaks through the ocean surface slowly becoming an island
- Eventually it breaks away from the hot center and moves south east, and another submarine volcano grows in its place
- Someday the island with the extinct volcano will begin to sink back into the – usually around 1 cm per century. As that begins, coral reefs grow up around it, creating lagoons, which create barrier reefs which stand as the old margin of the original island.
Cite: Stanley, D., South Pacific Handbook.