Yellowstone supervolcano eruption 'would affect the world'
11 December 2013 Last updated at 09:57 GMT
Scientists are reporting that the supervolcano lying beneath Yellowstone National Park in the US is far bigger than was previously thought, stretching for more than 90km (55 miles).
Dr James Farrell from the University of Utah told the Today programme that as the last major eruption took place 640,000 years ago, "nobody's ever witnessed one of these large supervolcanic eruptions", but he added that previous examples are believed to have been 2,000 times the size of the 1980 eruption in Mount St Helens.
If an eruption did take place, he said, then "it would affect the world".
"All the material that is shot up into the atmosphere [during an eruption] would eventually circle the Earth and affect the climate throughout the world."
However, Mr Farrell explained that he was certain no imminent eruptions would take place in the near future.
First broadcast on BBC Radio 4's Today programme on Wednesday 11 December 2013.