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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 and gaz 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 the BBC popular science programme, Horizon, in 2000 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 not so great as 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 the following:

  • Aira Caldera, Kyūshū, Japan
  • Aso, Kyūshū, Japan
  • Campi Flegrei, Campania, Italy
  • Kikai Caldera, Ryūkyū Islands, Japan
  • Long Valley Caldera, California, United States
  • Lake Taupo, North Island, New Zealand
  • Lake Toba, Sumatra, Indonesia
  • Valle Grande, New Mexico, United States
  • Yellowstone Caldera, Wyoming, United States
  • The most recent eruption was at Lake Toba, Sumatra, and occurred around 74,000 years ago, plunging the Earth into a volcanic winter.

A super-volcano is 12 times more likely than a large meteorite impact (0.15% probability that one will happen in our lifetime). Scientists estimate that approximately every 50,000 years the Earth experiences a super-volcano. More than 1,000 sq km of land can be obliterated by pyroclastic ash flows, the surrounding continent is coated in ash and sulphur gases are injected into the atmosphere, making a thin veil of sulphuric acid all around the globe and reflecting back sunlight for years to come. Daytime becomes no brighter than a moonlit night.

Taupo in New Zealand was the most recent super-volcano, around 26,500 years ago. However, the most damaging super-volcano in human history was Toba, on Sumatra, Indonesia, 74,000 years ago. Because it was fairly close to the equator it injected gas quickly into both hemispheres. Ice core data shows that temperatures were dramatically reduced for five to six years afterwards, with freezing conditions right down to the tropics. More recently, in 1783, the Laki volcano in Iceland erupted, spitting out three cubic miles of lava. Floods, ash, and fumes wiped out 9,000 people and 80 percent of the livestock. The ensuing starvation killed a quarter of Iceland's population. Atmospheric dust caused winter temperatures to plunge by 9 degrees in the newly independent United States.

Places to watch now are those that have erupted in the past, such as Yellowstone in the US and Toba. But, against all odds, a super-volcano could also burst out from a place with no present volcanic activity, such as under the Amazon jungle.


Large igneous provinces

Large igneous provinces are remains of mega-colossal flood basalts 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. Sulfurous volcanic gases produce acid rains. Chlorine-bearing compounds present yet another threat to the fragile ozone layer--a noxious brew all around. While they are causing short-term destruction, volcanoes also release carbon dioxide that yields long-term greenhouse-effect warming.
Prehistoric flood basalts significantly large enough to form these large igneous provinces 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. The last big pulse of flood-basalt volcanism built the Columbia River plateau about 17 million years ago. Large igneous provinces include eruption events at:

  • Brazilian Highlands, Brazil
  • Columbia River Plateau, United States
  • Deccan Traps, India
  • Siberian Traps, Russian Federation

The two largest flood basalt events in historic time have been at Eldgjá and Lakagigar, both in Iceland. Both of these altered the landscape around them, but neither of these had an impact great enough to be considered supervolcanic events.

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