This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Explosive volcanic eruptions can be as destructive as they are difficult to predict, launching pyroclasts—the fragments of magma and rock blasted from a volcano—into the air and surrounding areas. These particles can have wide-ranging impacts, as seen during this summer's eruption of Mount Etna in Italy, when ash fell over the nearby city of Catania and closed its international airport for weeks.
The size of erupted pyroclasts helps determine how far they travel and the hazards they pose. However, exactly how and where they form has remained poorly understood. "They disrupt air traffic, they disrupt road traffic, and then you still have to remove them, and you still need to clean up and see their effect on crops, plants, vegetation in general, and wildlife," says Jacopo Taddeucci, a volcanologist at Italy's Istituto Nazionale di Geofisica e Vulcanologia.
"It is important to understand how these particles are formed, because that controls their features." A study published in Geology, led by Taddeucci, shows that the fragmentation process that forms pyroclasts is more extensive than simplified eruption models often assume. Using scanning electron microscopy (SEM) and X-ray microtomography, the team analyzed pyroclasts from three mafic, or basaltic, volcanoes—Etna and Stromboli in Italy, and Cumbre Vieja in Spain—and linked their microscopic textures to formation conditions during different phases of eruption. By identifying and quantifying microtextures, including broken crystals, sutures and incorporated clasts, Taddeucci and colleagues found that fragmentation occurs across several stages rather than at a single depth and moment.
"This process is not occurring at a single point in space and time, but it's protracted," Taddeucci says. "It's something that covers a span of time and a span of spaces that goes from inside the volcano to outside a volcano." Scientists had already observed multiple fragmentation events outside volcanoes, including bombs and lapilli breaking apart in the air. This study provides the first microtextural evidence that fragmentation is also protracted inside a volcano, where it cannot be observed directly.
The team also showed that crack healing and the welding together of pyroclasts can be just as important as fragmentation in controlling final particle size. "We are getting more and more evidence that not only the breaking of the magma controls the size of the particles, but also the fact that different particles can stick together after they are broken," Taddeucci says. Because particle size influences how pyroclasts are dispersed, this finding could refine assumptions used in computer models of eruptions.
When asked whether the same microtextures would appear in products from Etna's eruption this summer, Taddeucci did not hesitate: "Oh, yes, of course," he says. "Most basaltic eruptions that are explosive in nature will produce these kinds of features." The microtextures can also be preserved in rocks from past eruptions, offering researchers a way to reconstruct earlier fragmentation conditions and improve models of future eruptions. "That's a big advantage we have with respect to earthquakes or other disasters that don't leave such a nice record," Taddeucci says.
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