A supervolcano refers to a volcano that produces the largest and most voluminous kinds of eruption on Earth. The actual explosivity of these eruptions varies, but the sheer volume of ejected tephra is enough to radically alter the landscape and severely impact global climate for years, with a cataclysmic effect on life (see also volcanic winter).
The term was originally coined by the producers of the BBC popular science program, Horizon, in 2000 to refer to these types of eruption. That investigation brought the subject more into the public eye, leading to further studies of the possible effects.
At first, supervolcano was not a technical term used in volcanology, but more recently, in 2003 and 2004, the term has been used in articles.
Though there is no well-defined minimum explosive size for a "supervolcano", there are at least two types of volcanic eruption that have been identified as supervolcanoes: massive eruptions and large igneous provinces.
Eruptions with a Volcanic Explosivity Index of 8 (VEI-8) are mega-colossal events that eject at least 1000 km³ of pyroclastic material.
VEI-8 eruptions are so powerful that they form circular calderas rather than mountains because the downward collapse of land at the eruption site fills emptied space in the magma chamber beneath. The caldera can remain for millions of years after all volcanic activity at the site has ceased.
VEI-8 volcanic events have included eruptions at the following locations. Estimates of the volume of erupted material are given in parentheses.
Lake Taupo, North Island, New Zealand - Oruanui eruption 26,500 years ago (1,170 km³)
Lake Toba, Sumatra, Indonesia - 75,000 years ago (2,800 km³)
Yellowstone Caldera, Wyoming, United States - 2.2 million years ago (2,500 km³) and 640,000 years ago (1,000 km³)
La Garita Caldera, Colorado, United States - Source of the truly enormous eruption of the Fish Canyon Tuff 27.8 million years ago (~5,000 km³)
The Lake Toba eruption plunged the Earth into a volcanic winter, eradicating an estimated 60%[1] [2] [3] [4] [5]of the human population (although humans managed to survive even in the vicinity of the volcano[6] ), and was responsible for the formation of sulfuric acid in the atmosphere.
Many other supermassive eruptions have also occurred in the geological past. Those listed below measured 7 on the VEI scale. Most of these were larger than Tambora's eruption in 1815 (160 km³), which was the largest eruption in recorded history.
Aira Caldera, Kyūshū, Japan - 22,000 years ago (110 km³)
Aso, Kyūshū, Japan - four large explosive eruptions between 300,000 to 80,000 years ago (Total volume 600 km³)
Kikai Caldera, Ryukyu Islands, Japan - 6,300 years ago (150 km³ (bulk volume))
Lake Taupo, North Island, New Zealand - 181 AD (100 km³)
Long Valley Caldera, California, United States - 760,000 years ago (600 km³)
Valle Grande, New Mexico, United States - 1.12 million years ago (~600 km³)
Yellowstone Caldera, Wyoming, United States - 1.3 million years ago (280 km³)
Bennett Lake Volcanic Complex, British Columbia/Yukon, Canada - 50 million years ago (850 km³)
Bruneau-Jarbidge, Idaho, United States - 10-12 million years ago (>250 km³) (responsible for the Ashfall Fossil Beds 1,600 km to the east[7])
Campi Flegrei, Naples, Italy - 12,000 years ago (Could be as much as 300 km³)
http://en.wikipedia.org/wiki/Supervolcano