Supervolcano eruption mystery solved

Supervolcanoes like Yellowstone can explode without an earthquake or other external trigger, experts have found.

The sheer volume of liquid magma is enough to cause a catastrophic super-eruption, according to an experiment at the European Synchrotron Radiation Facility (ESRF) in Grenoble.

Simulating the intense heat and pressure inside these "sleeping giants" could help predict a future disaster.

The study by a Swiss team from ETH Zurich appears in Nature Geoscience.

Lead author Wim Malfait, of ETH Zurich said: "We knew the clock was ticking but we didn't know how fast: what would it take to trigger a super-eruption?

"Now we know you don't need any extra factor - a supervolcano can erupt due to its enormous size alone.

"Once you get enough melt, you can start an eruption just like that."

There are about 20 known supervolcanoes on Earth - including Lake Toba in Indonesia, Lake Taupo in New Zealand, and the somewhat smaller Phlegraean Fields near Naples, Italy.

Super-eruptions occur rarely - only once every 100,000 years on average. But when they do occur, they have a devastating impact on Earth's climate and ecology.

When a supervolcano erupted 600,000 years ago in Wyoming, in what today is Yellowstone National Park, it ejected more than 1,000 cubic km of ash and lava into the atmosphere - enough to bury a large city to a depth of a few kilometres.

Lake Toba in Sumatra was formed during the eruption of a supervolcano 74,000 years ago

This ejection was 100 times bigger than Mount Pinatubo in the Philippines in 1992 and dwarfs even historic eruptions like Krakatoa (1883).

"This is something that, as a species, we will eventually have to deal with. It will happen in future," said Dr Malfait.

"You could compare it to an asteroid impact - the risk at any given time is small, but when it happens the consequences will be catastrophic."

Being able to predict such a catastrophe is obviously critical. But the trigger has remained elusive - because the process is different from conventional volcanoes like Pinatubo and Mount St Helens.

One possible mechanism was thought to be the overpressure in the magma chamber generated by differences between the less dense molten magma and more dense rock surrounding it.

"The effect is comparable to holding a football under water. When you release it, the air-filled ball is forced upwards by the denser water around it," said Wim Malfait, of ETH Zurich.

But whether this buoyancy effect alone was enough was not known. It could be that an an additional trigger - such as a sudden injection of magma, an infusion of water vapour, or an earthquake - was required.

More Information: dx.doi.org/10.1038/ngeo2042