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Will a Volcanic Eruption Be a Burp or a Blast?

“Having found something that tells us, yeah, if you have that kind of seismicity the viscosity goes up, and if it goes over that threshold it could be more explosive, that’s super cool,” Soldati said. “For surveillance and hazards, it actually has the potential to have an impact now.”

Nanoscopic nuisances

Many factors influence the viscosity of magma. One in particular has been overlooked, mainly because it’s almost invisible.

Danilo Di Genova, a geoscientist at the University of Bayreuth in Germany, studies nanolites, crystals about a hundredth the size of an average bacteria. They are believed to form at the top of the conduit when magma spurts out there. If you get enough of these crystals, they can trap magma, trap trapped gas, and increase viscosity. But unless you have very powerful microscopes to look at the freshly erupted lava, they will be imperceptible.

Di Genova has long been interested in the formation of nanolites. His experiments using silicon oil – a substitute for basalt, a common flowing magma – showed that if only 3 percent of an oil particle mixture is made up of nano-sized particles, the viscosity increases.

Researchers have studied nanolites in the laboratory by melting basalt rock into magma. The rock is heated inside a platinum crucible.Courtesy of Danilo Di Genova

He then turned to reality. He and his colleagues attempted to simulate what magma would feel as it rose through a conduit to the surface. They subjected Etna’s laboratory-molten basalt rock to gradual warming, pulses of sudden cooling, hydration, and dehydration. Sometimes they put the magma inside a synchrotron, a type of particle accelerator. In this craft, powerful X-rays interact with the atoms of a crystal to reveal their properties and, if the crystals are small enough, their existence.

As reported last year in Scientists progress, the experiments gave the team a working model of nanolite formation. If an eruption begins and the magma suddenly accelerates through the duct, it quickly depressurizes. This allows the water to come out of the molten rock and form bubbles, which dehydrates the magma.

This action changes the thermal properties of magma, which greatly facilitates the presence of crystals even at extremely high temperatures. If the ascent of the magma is fast enough and the magma is quickly dehydrated, a cornucopia of nanolites is formed, which greatly increases the viscosity of the magma.

This change does not give a noticeable signal. But just knowing it exists, Di Genova said, may allow researchers to explain why otherwise flowing magma volcanoes, like Vesuvius or Etna, can sometimes produce epic explosions. Seismic signals can trace the rate at which magma is rising, so perhaps this can be used to predict a last minute nanolite population boom, which leads to a catastrophic explosion.

Sweeping away the fog

These advances aside, scientists are still a long way from replacing eruption probabilities with certainties.

One reason is that “most of the world’s volcanoes are not very well monitored,” said Seth Moran, a seismologist researcher at the US Geological Survey’s Cascades Volcano Observatory. This includes many American Cascade volcanoes, several of which have a propensity for giant explosions. “It’s not easy to predict an eruption if there are enough instruments on the ground,” Roman said. “But it is very, very difficult to predict an eruption if there are no instruments on the volcano.”

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