The world's biggest bang
A global disaster never witnessed by modern man may one day mushroom above the pine forests and hot springs of Yellowstone National Park in the United States.
While ordinary volcanoes can kill thousands of people and destroy entire cities, it's thought a supervolcano could claim up to a billion lives and devastate continents.
"A super-eruption is the world's biggest bang", says Prof. Bill McGuire of the Benfield Greig Hazard Research Centre at the University of London. "It's a volcanic explosion big enough to dwarf all others and with a reach great enough to affect everyone on the planet".
Heavy stuff: Ash from the 1991 eruption of Mount Pinatubo in the Philippines settles on the tail section of a World Airways DC-10, causing it to tilt onto its rear wheels.
It's very likely a super-eruption would shutdown airports worldwide.
Considering their destructive potential, it's a good thing super-eruptions are so rare – the last one happened in Toba, Indonesia, about 74,000 years ago. Geologists think these eruptions take place about every 50,000 years, which suggests one is overdue.
About 40 supervolcanoes are dotted across the globe. There are two in Britain – one in Glencoe, Scotland, the other in Scafell in the Lake District. However, most supervolcanoes, including those in Britain, burned out long ago.
Yellowstone, located in the western state, Wyoming, is a dormant supervolcano, which means a major eruption could happen in the future. But before you get worried, it's important to remember that most volcano experts say a Yellowstone super-eruption is probably a long way off, or it may never happen at all.
Super size: About 2.1 m years ago the Yellowstone supervolcano erupted 2,500 times more ash than Mount St Helens (pictured).
Read about the 1980 Mount St Helens eruption on BBC On This Day.
"It's far more likely, if there is an eruption, it'll be on a small scale, perhaps comparable to Mt St Helens," says volcano expert Prof. Steve Sparks of the University of Bristol.
Although they're called 'super', most people would have trouble spotting a supervolcano. Their main feature is a large magma chamber, which is an underground reservoir filled with flowing, hot rock under huge pressures.
Some stats on the Yellowstone supervolcano:
- A super-eruption would equal the force of 1,000 Hiroshima atomic bombs exploding every second.
- You could fit Tokyo, the world's biggest city, in Yellowstone's super-volcanic crater.
- Three super-eruptions at Yellowstone appear to have occurred on a 600,000-700,000 year cycle starting 2.1 million years ago. The most recent took place 640,000 years ago – suggesting Yellowstone is overdue for an eruption.
Continue to page two and find out how much volcanic ash it takes to collapse a roof.
The US Geological Survey has more information about the Yellowstone supervolcano.
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