Study says Yellowstone magma underestimated

Swirling in a semi-viscous cauldron of intense heat beneath the beauty of Yellowstone National Park is a potent chamber of molten rock, waiting to explode in a huge “supervolcano”.

Now seismologists say there is two-and-a-half the volume of magma than had previously been 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.

An eruption would be devastating, and not just locally.

“It would be a global event,” said lead study author Jamie Farrell of the University of Utah,

“There would be a lot of destruction and a lot of impacts around the globe.”

The last Yellowstone eruption happened 640,000 years ago, according to the US Geological Survey. For years, observers tracking earthquake swarms under Yellowstone have warned the caldera is overdue to erupt.

Farrell dismissed that notion, saying there wasn’t enough data to estimate the timing of the next eruption.

“We do believe there will be another eruption, we just don’t know when,” he said.

By measuring seismic waves from earthquakes, scientists were able to map the magma chamber underneath the Yellowstone caldera as 55 miles (88.5km) long and 18 miles (29km) wide.

The chamber runs at depths from three to nine miles (five to 15km) below the earth’s surface.

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.

Careful monitoring continues

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.

There are enough instruments monitoring the seismic activity of Yellowstone that scientists would likely know well ahead of time if there was unusual activity happening and magma was moving to the surface, Farrell said.

The USGS Yellowstone Volcano Observatory listed the park’s volcano alert level as “normal” for December.

Yellowstone attracts millions of visitors with its geothermal features of geysers, hot springs and bubbling mud pots, and opened its gates on Sunday for its winter season.

A large earthquake at Yellowstone is much more likely than a supervolcano eruption, Farrell said.

The 7.5-magnitude Hebgen Lake earthquake killed 28 people there in 1959.

Brigham Young University geology professor Eric Christiansen said the study by Farrell and University of Utah Professor Bob Smith was very important to understanding the evolution of large volcanos such as Yellowstone’s.

“It helps us understand the active system,” Christiansen said. “It’s not at the point where we need to worry about an imminent eruption, but every piece of information we have will prepare us for that eventuality.”