How Did Hawaii Form?

Hawaii's unusual volcanic activity, far from tectonic plate boundaries, is due to its location over a hotspot. This hotspot is fueled by a mantle plume of superheated rock rising from the Earth's core, pushing up the crust and melting into magma.

Magma seeps through cracks to the surface, becoming lava. Hawaiian volcanoes produce fluid basaltic lava, unlike the more explosive volcanoes. This creates gently sloping volcanoes, often with visible lava lakes at their summits, like Kilauea. Magma can also erupt from fissures, and when lava meets the ocean, it grows the island, though the resulting steam is a dangerous mixture of hydrochloric acid and volcanic glass shards.

The Pacific plate's movement to the northwest drags the crust over the stationary hotspot, creating a chain of islands. The oldest islands, Niihau and Kauai, are about five million years old, while the Big Island is a much younger 400,000 years old and still has four active volcanoes. Eventually, the Big Island will move off the hotspot, and a new island, like Loihi, will emerge in approximately 200,000 years.