the island is seven separate shield volcanos that erupted more or less one at a time, one partly covering the other. these are (from oldest to youngest): kohala (extinct), mauna kea (dormant), hualalai (dormant), mauna loa (active), kulani (extinct, mostly buried), and kilauea (very active). the volcanos were caused by the pacific oceanic tectonic plate moving over a hotspot. there lava from the earth's lower mantle or upper core is close to the surface.