Volcano: A rupture in a planetary crust that allows magma, ash, and gases to escape from a magma chamber beneath the surface. Magma chamber: A large pool of liquid rock beneath the surface of the Earth. Tectonic plates: Massive slabs of solid rock that make up Earth's lithosphere and move 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 toward each other. Hotspot: A location in the mantle where a persistent plume of magma rises to the crust, creating a series of volcanoes. Volcanic winter: A reduction in global temperatures caused by volcanic ash and sulfuric acid droplets obscuring the Sun.