Volcano: A rupture in the crust of a planetary-mass object that allows hot lava, ash, and gases to escape from below the surface. Plate tectonics: A scientific theory describing the large-scale motion of Earth's lithosphere. Hotspot: A location on Earth's surface that has experienced volcanism for a long period, often attributed to a mantle plume. Mantle plume: A proposed upwelling of abnormally hot rock within the Earth's mantle. Supervolcano: A volcano that has had an eruption with a Volcanic Explosivity Index (VEI) of 8, the largest recorded value on the index. Submarine volcano: A volcanic formation located beneath the ocean surface. Subglacial volcano: A volcanic formation that exists beneath a glacier or ice sheet. Mud volcano: A geological formation created by the eruption of mud or slurries, gases, and water.