Island formation. Computer illustration showing the process of island formation in the Hawaii island chain, USA. The chain was formed by molten rock (magma) erupted from volcanoes as the Pacific Plate of the Earth's crust slowly moves over a hot spot in the molten mantle below it. The arrow indicates the direction of movement. Big Island (green), the largest island in the chain, is at upper right. The plate's movement means that magma (bottom right) is now also being erupted from the submarine volcano Loihi Seamount. Loihi may one day rise above the water's surface to become the ninth main Hawaiian Island.