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A supervolcano refers to a volcano that produces the largest and most voluminous kinds of eruptions on earth. The actual explosivity of these eruptions varies, but the sheer volume of extruded magma is immense enough to radically alter the landscape and severely impact global climate for years, with a cataclysmic effect on life. The term was originally coined by the producers of a BBC popular science programme in 2002 to refer to these types of eruptions. It is not a technical term used in volcanology. Though there is no well-defined minimum size for a "supervolcano", there are at least two types of volcanic eruption that have been identified as supervolcanoes.
Volcanic Explosivity Index-8 eruptions (VEI-8 for short) are mega-colossal events that extrude at least 1000 km³ of magma and pyroclastic material. Such an eruption erases virtually all life in a radius of hundreds of kilometers from the site, and entire continental regions further out can be buried meters deep in ash. VEI-8 eruptions are so great as not to form mountains, but instead circular calderas, resulting from the downward collapse of land at the eruption site to fill emptied space in the magma chamber beneath. The caldera can remain for millions of years after all volcanic activity at the site has died. VEI-8 volcanic events have included eruptions at:
- Mount Aniakchak, Alaska, United States
- Aso, Kyūshū, Japan
- Campi Flegrei, Campania, Italy
- Kikai Caldera, Ryūkyū Islands, Japan
- Long Valley Caldera, California, United States
- Mount Mazama, Oregon, United States (now Crater Lake)
- Lake Taupo, North Island, New Zealand
- Lake Toba, Sumatra, Indonesia
- Valle Grande, New Mexico, United States
- Mount Warning, New South Wales, Australia
- Yellowstone Caldera, Wyoming, United States
Basaltic floods are unexplosive volcanic eruptions that extrude enormous quantities of basaltic lava flat and deep over large areas, even covering entire sections of continent. Though not explosive, the gases and dust released by such an eruption impact global climate as much as a VEI-8, hence a supervolcano. Prehistoric basaltic floods have been suspected as causes or contributors to mass extinctions in the past, including the ultra-massive Permian extinction, which killed the majority of all then-living species, and the more famous but smaller Cretaceous extinction that extinguished most of the dinosaurs. Basaltic flood events have included eruptions at:
The two largest basaltic flood events in historic time have been at Eldgjá and Lakagigar, both in Iceland. Neither of these had an impact great enough to be considered supervolcanic events.
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