A Yellowstone volcano eruption would dwarf that of Mount St Helens

The hot molten rock beneath America's Yellowstone National Park is 2.5 times larger than previously estimated, meaning the park's supervolcano has the potential to erupt with a force about 2,000 times the size of Mount St Helens, according to a new study.

By measuring seismic waves from earthquakes, scientists were able to map the magma chamber underneath the Yellowstone caldera as 88 kilometres long, lead author Jamie Farrell of the University of Utah said.

The chamber is 29 kilometres wide and runs at depths from five to 14.5 kilometres below the earth's surface, he added.

That means there is enough volcanic material below the surface to match the largest of the supervolcano's three eruptions over the last 2.1 million years, Farrell said.

The largest blast - the volcano's first - was 2,000 times the size of the 1980 eruption of Mount St Helens in Washington state. A similar one would spew large amounts of volcanic material in the atmosphere, where it would circle the earth, he said.

"It would be a global event," Farrell said. "There would be a lot of destruction and a lot of impacts around the globe."