The
Yellowstone Super Volcano
A Guest Document from BBC
February 3, 2000
INTRODUCTION
The threat of climate change caused by human activity could turn out to
be a minor problem by comparison with a scarcely acknowledged natural
hazard.
Geologists say there is a real risk that sooner or later a supervolcano
will erupt with devastating force, sending temperatures plunging on a
hemispheric or even global scale.
A report by the BBC Two programme Horizon on one supervolcano, at
Yellowstone national park in the US, says it is overdue for an eruption.
Yellowstone has gone off roughly once every 600,000 years. Its last
eruption was 640,000 years ago.
Professor Bill McGuire, of the Benfield Greig Hazard Research Centre at
University College, London, told BBC News Online: "We're getting ready
for another eruption, unless the system has blown itself out.
"But the ground surface deformation and other signs measured by
satellite suggest it's still active, and on the move."
DETAILS
Molten rock
Typically, supervolcanoes are not mountains but depressions, huge
collapsed craters called calderas, which are hard to detect.
The Yellowstone caldera is 70 kilometres long and 30 km wide. Eight km
beneath the Earth's surface lies a huge magma chamber, containing vast
amounts of molten rock.
As pressure rises in the chamber, the surface is also rising and there
is a measurable increase in heat. But vulcanologists do not know when
Yellowstone will blow.
Supervolcanoes are relate to giant
calderas
Professor McGuire, whose book, Apocalypse! A natural history of global
disasters, portrays a possible Yellowstone explosion in 2074, says
there have been two such events every 100,000 years for the last two
million years.
The areas where supervolcanoes are most likely to be found, he says,
are subduction zones, where the Earth's plates are dipping below one
another. The Pacific Rim and southeast Asia are especially vulnerable.
But there is a caldera in the Phlegraean Fields near Naples in southern
Italy. Dr Ted Nield, of the Geological Society of London, told BBC News
Online: "It could do the same as Yellowstone, though on a smaller
scale".
Nuclear winter
"When a supervolcano goes off, it is an order of magnitude greater than
a normal eruption. It produces energy equivalent to an impact with a
comet or an asteroid.
"You can try diverting an asteroid. But there is nothing at all you can
do about a supervolcano.
"The eruption throws cubic kilometres of rock, ash, dust, sulphur
dioxide and so on into the upper atmosphere, where they reflect
incoming solar radiation, forcing down temperatures on the Earth's
surface. It's just like a nuclear winter.
"The effects could last four or five years, with crops failing and the
whole ecosystem breaking down. And it is going to happen again some
day."
Ice-core records show that the eruption of Toba in Sumatra about 74,000
years ago may have caused global cooling of from three to five degrees
Celsius, and perhaps as much as 10 degC during growing seasons in
middle to high latitudes.
Even ordinary volcanoes can affect the climate.
Published in 2000
The M+G+R Foundation
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