A supervolcano is a volcano capable of producing a volcanic eruption with an ejecta volume greater than 1,000 km3 (240 cu mi). This is thousands of times larger than normal volcanic eruptions. Supervolcanoes can occur when magma in the mantle rises into the crust from a hotspot but is unable to break through the crust. Pressure builds in a large and growing magma pool until the crust is unable to contain the pressure. They can also form at convergent plate boundaries (for example, Toba) and continental hotspot locations (for example, Yellowstone).
Although there are only a handful of Quaternary supervolcanoes, supervolcanic eruptions typically cover huge areas with lava and volcanic ash and cause a long-lasting change to weather (such as the triggering of a small ice age) sufficient to threaten species with extinction.
Read more about Supervolcano: Terminology, Large Igneous Provinces, Massive Explosive Eruptions, Ongoing Studies, Media Portrayal