Volcano: A rupture in a planetary crust that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. Tectonic Plates: Massive slabs of solid rock composing the Earth's lithosphere, moving over the asthenosphere. Divergent Boundary: A tectonic boundary where two plates move away from each other. Convergent Boundary: A tectonic boundary where two plates move towards each other, often causing one to subduct beneath the other. Hotspot: A volcanic region thought to be fed by underlying mantle that is anomalously hot compared with the surrounding mantle. Mantle Plume: A proposed mechanism of convection within the Earth's mantle that pushes up the crust, forming hotspots and volcanic activity. Volcanic Arc: A chain of volcanoes formed above a subducting plate. Supervolcano: A volcano that has had an eruption with a Volcanic Explosivity Index (VEI) of 8, the largest recorded value on the index.