Earth’s rocky outer shell, its crust, is actually made of dozens of huge pieces of rock known as tectonic plates. These plates ride on currents of molten rock in the upper mantle, which lies just below the crust. Activity in the mantle and crustal plates results in earthquakes and volcanic eruptions. Most of these seismic events take place where two plates come together or tear apart.

The Hawaiian Islands, however, sit in the middle of the Pacific plate. They lie over a hot spot, where magma from the mantle pushes to the surface. The Hawai'i hot spot remains in one place while the Pacific plate moves steadily northwest. Hawai'i’s “Big Island” is still being formed by Mauna Loa and Kilauea, two volcanoes currently sitting over the hot spot. Loihi, an undersea volcano, also sits above the hot spot and will likely become the next Hawaiian island.