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

Early Warning System for Super Volcano Eruptions

Scientists can't predict the exact time when a volcano will erupt but clues from an ancient super-volcano explosion could reveal ways to calculate when the next massive eruption.

Earth is littered with roughly one dozen super-volcanoes that can cause more havoc than ordinary volcanoes.

For example, Mount Toba on the Indonesian island of Sumatra released 700 cubic miles of magma and a thick layer of ash over South Asia when it erupted 74,000 years ago.

Compared to the largest eruption in recorded history, the explosion of Krakatoa in 1883 which only released 3 cubic miles of volcanic material, super-volcano eruptions are more devastating.

When a super-volcano erupts it has the potential to trigger global catastrophic events so predicting when one is about to erupt is vital.

Unfortunately, super-volcanoes can lie dormant for thousands of years before blowing so scientists haven't been able to monitor the pre-eruption events as closely as they have with volcanoes.

"When volcanoes awaken and when the magma starts to ascend to the surface, cracking rock as it does, it sends out signals," Professor Tim Druitt, a volcanologist at France's Blaise Pascal University and lead researcher stated.

"You get seismic signals, you get deformation of the surface, increasing gas emission at the surface - and this can be detected.

"The question we're addressing here is what's going on at depth prior to these big eruptions. The classical view was that during long repose periods over thousands of years, magma slowly accumulates a few kilometers below the volcano and finally it blows."

To learn more about super-volcanoes and the signs leading up to an eruption, the researchers studied the remnants of another cataclysmic volcanic explosion, the Santorini eruption 3,600 years ago that may have inspired the legend of the lost city of Atlantis.

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