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    Friday, December 08, 2006


    Other Lesser, Catastrophic Explosive Eruptions


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    For the docudrama, see Supervolcano (docudrama)

    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 extruded magma is enough to radically alter the landscape and severely impact global climate for years, with a cataclysmic effect on life (see also nuclear winter).



    Word origin

    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.

    Large igneous provinces

    A large igneous province (LIP) is an extensive region of basalts on a continental scale, resulting from flood basalt eruptions. When created, these regions often occupy several million km² and have volumes on the order of 1 million km³. In most cases, the majority of this is laid down over an extended but geologically sudden period of less than 1 million years.

    Massive eruptions

    Eruptions with a Volcanic Explosivity Index of 8 (VEI-8) are mega-colossal events that extrude at least 1000 km³ of magma and pyroclastic material.

    Such an eruption would erase virtually all life within 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 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.

    Known eruptions

    Satellite image of Lake Toba.
    Satellite image of Lake Toba.

    VEI-8 volcanic events have included eruptions at the following locations. Estimates of the volume of erupted material are given in parentheses.

    The Lake Toba eruption plunged the Earth into a volcanic winter, eradicating an estimated 60%[1] [2] [3] [4] [5]of the human population, and was responsible for the formation of sulfuric acid in the atmosphere and the Millennial Ice Age.

    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, which was the largest eruption in recorded history.

    For large flood basalt eruptions, see large igneous province.

    Media portrayal

    A two-part television docudrama entitled Supervolcano was shown on BBC, the Discovery Channel, and other television networks worldwide. It looked at the events that could take place if the Yellowstone supervolcano erupted. It featured footage of volcano eruptions from around the world and computer-generated imagery depicting the event. According to the program, such an eruption would have devastating effect across the globe and would cover virtually all of the United States with at least 1 cm of volcanic ash, causing mass destruction in the nearby vicinity and killing plants and wildlife across the continent. The dramatic elements in the program were followed by Supervolcano: The Truth About Yellowstone, a documentary about the evidence behind the movie. The program had originally been scheduled to be aired in early 2005, but it was felt that this would be insensitive so soon after the 2004 Indian Ocean earthquake. The program and its accompanying documentaries were released on DVD region 2 simultaneously with its broadcast.

    A National Geographic documentary called Earth Shocks portrayed the destructive impact of the rapid eruption of Lake Toba some 75,000 years ago and caused a phenomenon known as the Millennial Ice Age that lasted for 1000 years and wiped out more than 60%[7] [8] [9] [10] [11] of the global population of the time. An eruption of the Yellowstone supervolcano was originally one of the scenarios depicted in the docu-drama End Day, but was excluded from all airings to date for unknown reasons and is only presently mentioned at the show's BBC website.

    See also

    Volcanic winter

    From Wikipedia, the free encyclopedia

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    A volcanic winter is the reduction in temperature caused by volcanic ash and droplets of sulfuric acid obscuring the sun, usually after a volcanic eruption.



    Effects on life

    The causes of the bottleneck phenomenon, i.e., a sharp decrease in a species' population immediately followed by a period of great genetic divergence (differentiation) among survivors—might be attributed to volcanic winters. According to anthropologist Stanley Ambrose, such events diminish the population size to "levels low enough for evolutionary changes, which occur much faster in small populations, to produce rapid population differentiation".

    Ancient case of volcanic winters

    A terrific case of volcanic winter happened around 71,000–73,000 years ago following the supereruption of Lake Toba on Sumatra island (Indonesia). In the following 6 years there was the highest amount of volcanic sulphur deposited in the last 110,000 years, possibly causing complete deforestation in Southeast Asia and the cooling of sea temperatures by 3–3.5°C. Remarkably, the eruption almost caused an instant Ice Age on Earth by accelerating the glacial shift that already was going on, therefore causing massive population reduction among animals and human beings on Earth.

    This, combined with the fact that most human differentiations abruptly occurred at that same period, is a probable case of bottleneck linked to volcanic winters (see Toba catastrophe theory). On average, such super-eruptions and subsequent volcanic winters occur on our planet every 50,000 years.

    Recent cases of volcanic winter

    Pinatubo early eruption 1991
    Pinatubo early eruption 1991

    The scales of recent winters are more modest but their effects can be significant. A paper written by Benjamin Franklin in 1783 blamed the unusually cool summer of 1783 on volcanic dust coming from Iceland, where the eruption of Laki volcano had released enormous amounts of sulfur dioxide, resulting in the death of much of the island's livestock and a catastrophic famine which killed a quarter of the population. Temperatures in the northern hemisphere dropped by about 1°C in the year following the Laki eruption.

    The 1815 eruption of Mount Tambora, a stratovolcano in Indonesia, occasioned mid-summer frosts in New York State and June snowfalls in New England in what came to be known as the "Year Without a Summer" of 1816.

    In 1883, the explosion of Krakatoa (Krakatau) also created volcanic winter-like conditions. The next four years after the explosion were unusually cold, and the winter of 1888 was the first time snow fell in the area. Record snowfalls were recorded worldwide.

    Most recently, the 1991 explosion of Mount Pinatubo, another stratovolcano, in the Philippines cooled global temperatures for about 2-3 years, interrupting the trend of global warming which had been evident since about 1970.

    Further Reading

    See also


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