Magma, the molten rock found beneath the Earth's surface, undergoes a complex process of breaking and healing during volcanic eruptions, new research suggests. This process was revealed through microscopic analysis of fragments known as pyroclasts—pieces of magma and rock expelled during eruptions. A recent example of this was the summer eruption of Mount Etna in Italy, where ash blanketed the nearby city of Catania, forcing the closure of its international airport for weeks. The size of these pyroclasts determines how far they travel and the dangers they pose, but the exact conditions under which they form have remained unclear. A study published in the journal Geology sheds new light on this phenomenon. Led by Jacopo Taddeucci, a volcanologist at Italy's Istituto Nazionale di Geofisica e Vulcanologia, the research examined pyroclasts from three mafic (basaltic) volcanoes: Etna and Stromboli in Italy, and Cumbre Vieja in Spain. Using advanced imaging techniques like scanning electron microscopy (SEM) and X-ray microtomography, the team analyzed the microscopic textures of these fragments, linking them to the conditions under which they formed during various stages of the eruptions. The study found that the process of fragmentation—where magma breaks into pyroclasts—is not a single event but occurs over multiple stages and locations. "This process is not occurring at a single point in space and time, but it's protracted," Taddeucci explains. "It spans a range of times and spaces, from inside the volcano to outside." While scientists had previously observed fragmentation events in the air, such as when volcanic bombs and lapilli break apart, this study provides the first evidence that the process also continues inside the volcano, where it can't be directly observed. The research also highlights the importance of crack healing and the welding of pyroclasts together, which can be just as significant as fragmentation in determining the final size of the particles. "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. This finding could improve computer models used to predict how pyroclasts are dispersed during eruptions. Taddeucci notes that the microtextures observed in the study would likely be present in pyroclasts from Etna's recent eruption. "Oh, yes, of course," he says. "Most basaltic eruptions that are explosive in nature will produce these kinds of features." These textures can also be preserved in rocks from past eruptions, giving researchers a way to reconstruct past fragmentation conditions and improve models for future eruptions. Taddeucci emphasizes that such research is only possible through international collaboration, working with colleagues across different observatories and institutions.