Vulcanologists closer to 'holy grail' of predicting violent eruptions through changes in magma

Violent volcanic eruptions could soon be predicted with greater accuracy following a study into how magma can suddenly explode from underground reservoirs. Scientists have analysed the chemical and physical changes in the magma of two active volcanoes and believe the analysis may soon be used to make better predictions of an impending eruption.

The new insights may be used in conjunction with existing methods of monitoring active volcanoes to produce better early-warning systems.

"We have a range of techniques for monitoring active volcanoes at the surface," Professor Jon Blundy, a vulcanologist at the University of Bristol told the British Association Festival of Science meeting at the University of East Anglia..

"In addition, petrologists look at the eruptive products of volcanoes and we try to extract information about what was going on before the eruption happened.

"They are like pathologists who work on cadavers trying to work out the cause of death. Developing links between what goes on underground prior to and during an eruption and what was measured at the surface is like the holy grail of modern vulcanology," Professor Blundy said.

The study, published in the journal Nature, analysed the liquid droplets contained in magma from the Shiveluch volcano in Russia's Kamchatka peninsula and Mount St Helens in Washington state, which erupted violently on 18 May 1980.

One of the key findings is that as crystals form in the magma - changing it from a fluid into a solid - its temperature does not fall as previously thought but rises by up to 100C. This is important because whether magma explodes from a volcano depends on a complex interaction of pressure, temperature and water content. As pressure falls, crystals form, temperature rises and water trapped in the magma turns to bubbles which propel the erupting magma. "Magma stored at high pressure contains quite a lot of water and has the potential to form a lot of bubbles, and the more bubbles, the more explosive the eruptions," Professor Blundy said.

"It's like taking a bottle of champagne and rather than removing the cork in a careful way, smashing the whole bottle after giving it a good shake first. That would be the May 18th eruption of Mount St Helens."

The findings suggest that magma ascending from deep underground reservoirs through "pipes" in the volcano may be able to heat itself up without the need of an extraneous heat source, such as a shot of hot magma from below.

The scientists believe the discovery changes what is known about the internal dynamics of a volcano and the understanding of what can trigger a violent eruption.

Mount St Helens threw out some magma a month before the eruption and this could have been analysed to assess the threat level, Professor Blundy said. "If we had available the technique we have now and been able to study that material that came out, it would have given us some clues as to what was going on underneath the volcano," he said.

"I'm not saying that we would have been able to predict that a month or so later the volcano was going to go off big time, but it would certainly have given us a clue as to what was going on underground at the time that might have helped to predict the future consequences of this magma movement," he said.

"The work we've done constitutes an important step towards understanding how magma moves beneath volcanoes."