A supervolcano is a volcano that can make a volcanic eruption where the things being thrown out of the volcano have a volume bigger than 1,000 km3 (240 cu mi), which is a Volcanic Explosivity Index (VEI) of 8. If the definition is expanded, supervolcanoes also include volcanoes that have volcanic eruptions with a volume bigger than 100 km3 (24 cu mi), which is a Volcanic Explosivity Index (VEI) of 7. This is thousands of times bigger than most volcanic eruptions which happened a long time. Supervolcanoes can occur when magma in the Earth rises into the crust from a hotspot, but can not break through the crust. More and more pressure builds up in a large and growing magma pool until the crust can no longer take the pressure.
Although there are not many Quaternary supervolcanoes, supervolcanic eruptions usually cover very big areas with lava and volcanic ash. They can also cause a long-lasting change to weather (such as the triggering of a small ice age), enough to possibly make species extinct.