Illustration depicting the formation of the Samoan Islands chain

Like Hawaii, the Samoan Islands form over a hotspot–a plume of hot, buoyant magma that rises from deep within Earth’s mantle and through its crust and erupts to form volcanic islands. The Samoan chain formed as the overlying Pacific Plate moved over the stationary hotspot. (Illustration by Jayne Doucette, © Woods Hole Oceanographic Institution)