“Having found something that tells us, yes, if you have this kind of seismicity, viscosity is increasing, and if it’s above this threshold, it could be more explosive—that is super cool,” said Soldati. “For monitoring and hazards, this actually has the potential to be impactful now.”
Many factors influence magma viscosity. One in particular has been overlooked, mostly because it’s nearly invisible.
Danilo Di Genova, a geoscientist at the University of Bayreuth in Germany, studies nanolites—crystals about one-hundredth of the size of your average bacterium. They are thought to form at the top of the conduit as magma gushes up it. If you get enough of these crystals, they can lock up the magma, imprison trapped gas, and increase the viscosity. But unless you have very powerful microscopes to look at freshly erupted lava, they’ll be imperceptible.
Di Genova has long been interested in how nanolites form. His experiments using silicon oil—a proxy for basalt, a commonplace runny magma—showed that if just 3 percent of an oil-particle mixture is made of nano-size particles, the viscosity spikes.
He then turned to the real thing. He and his colleagues attempted to simulate what magma would experience as it rose through a conduit to the surface. They subjected lab-melted basaltic rock from Mount Etna to gradual heating, pulses of sudden cooling, hydration, and dehydration. At times, they placed the magma inside a synchrotron, a type of particle accelerator. Within this contraption, powerful x-rays interact with a crystal’s atoms to reveal their properties and—if the crystals are small enough—their existence.
As reported last year in Science Advances, the experiments gave the team a working model of how nanolites form. If an eruption begins and magma suddenly accelerates up through the conduit, it rapidly depressurizes. That lets water come out of the molten rock and form bubbles, which dehydrates the magma.
This action changes the thermal properties of the magma, making it a lot easier for crystals to be present even at extremely high temperatures. If the magma’s ascent is sufficiently rapid and the magma is speedily dehydrated, a cornucopia of nanolites comes into being, which significantly increases the magma’s viscosity.
This change doesn’t give off a noticeable signal. But merely knowing it exists, said Di Genova, may enable researchers to explain why volcanoes with otherwise runny magma, like Vesuvius or Etna, can sometimes produce epic explosions. Seismic signals can trace how quickly magma is ascending, so perhaps that may be used to forecast a last-minute nanolite population boom, one that leads to a catastrophic blast.
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 that well monitored,” said Seth Moran, a research seismologist at the US Geological Survey’s Cascades Volcano Observatory. This includes many of America’s Cascades volcanoes, several of which have a propensity for giant explosions. “It’s not easy to forecast an eruption if there are sufficient instruments on the ground,” said Roman. “But it’s very, very difficult to forecast an eruption if there are no instruments on the volcano.”