Description from the author

An island chain is formed by the movement of oceanic crust above a lava hotspot, or magma plume. The position of the plume remains roughly the same, while the crust above is moving. The upwards movement of magma by convection leads to the magma erupting from the crust in a volcano. The magma cools, forming the land which becomes an island. Islands are gradually eroded by the ocean. Therefore, older islands who have been separated from the magma will be progressively smaller, allowing one to trace the path of the plate along the chain.