A team led by Alberto Caracciolo of the University of Perugia examined clinopyroxene crystals erupted during the El Charco eruption of 1712, the Teneguía eruption of 1971, and the Tajogaite eruption of 2021, the destructive nine-week event that devastated parts of the island and displaced thousands of residents. Clinopyroxene is an ideal mineral archive: it crystallizes over a wide range of depths, and its slow rates of chemical diffusion preserve trace element zoning that records the temperature, pressure, and composition of the magmas through which the crystal grew. By reading these zoned crystals like tree rings, the researchers reconstructed the pre-eruptive history of each eruption in remarkable detail.

The team combined quantitative trace element mapping by laser ablation inductively coupled plasma mass spectrometry, electron microprobe analyses, clinopyroxene-based thermobarometry, and unsupervised machine learning cluster analysis. The clustering, applied to more than 316 single-spot analyses and nearly 400,000 mapped pixels, resolved six geochemically distinct populations of clinopyroxene. Two of these populations, found exclusively in resorbed crystal cores, turned out to be the smoking gun for the deep evolved reservoir: they crystallized from melts so differentiated that up to 80 to 90 percent fractional crystallization of a primitive basanite would be required to generate them, matching the degree of differentiation needed to produce phonolite from basanite beneath La Palma.

Thermobarometry told the researchers where and how hot these processes occurred. Primitive clinopyroxene cores record crystallization pressures of roughly 6 to 9 kilobars, equivalent to depths of about 22 to 32 kilometers, well below the local Moho at 10 to 14 kilometers. Evolved cores, the green, sodium-rich crystals that grew in the phonolitic mush, record the coolest temperatures in the entire dataset, between 1000 and 1025 degrees Celsius, at depths of roughly 17 to 21 kilometers. In contrast, the primitive inner rims that overgrow these cores record much hotter conditions of 1100 to 1150 degrees Celsius, the signature of fresh, mafic basanitic magma invading the reservoir from below.

The geometry of the zoning is what makes the story so compelling. In nearly every crystal examined, a chromium-rich, magnesium-rich inner rim abruptly overgrows an evolved, resorbed core, marking the moment when hot basanitic recharge disrupted the resident mush and swept its antecrysts into the ascending magma. Using measured rim thicknesses of roughly 40 to 50 micrometers and growth rates borrowed from comparable alkaline systems such as Mount Etna, the team estimated that these recharge events occurred at least four to seven days before eruption. In other words, the crystals recorded a countdown: the mush was unlocked days to weeks before magma reached the surface.

Yet the recharge was not the immediate trigger. In the early-erupted tephrites, the recharge signature is followed by a slightly more fractionated rim composition, indicating that after the mafic input the system cooled and fractionated rather than erupting immediately. The authors argue that eruption onset was more likely driven by progressive pressurization of the reservoir as volatile exsolution during continued crystallization raised the internal overpressure until the surrounding rock failed. This interpretation is consistent with independent evidence from the 2021 Tajogaite eruption, where phase equilibrium experiments and olivine zoning indicate pre-eruptive cooling of the tephritic magma.

Perhaps the most remarkable result is the temporal consistency of the system. Across eruptions separated by as much as 259 years, the same crystal populations appear, the same storage depths recur, and the same recharge-to-fractionation trends hold. The microcrystalline matrix compositions, which serve as crystal-free proxies for the carrier melts, cluster around 4.7 to 4.9 weight percent MgO in all three eruptions, and thermodynamic fractional crystallization modeling shows that the transition from basanite to tephrite within each eruption required only about 10 to 20 percent crystallization. The plumbing system beneath Cumbre Vieja, in short, has been operating in a stable configuration for centuries, with magma storage dominantly in the upper mantle and only transient stalling in the crust at depths of roughly 5 to 10 kilometers, a zone also suggested by fluid inclusion data and shallow seismicity during the 2021 eruption.

To test whether this deep-mush model applies beyond La Palma, the team compiled clinopyroxene major element data from low-flux ocean island basalt volcanoes around the world, including the Canary Islands, Cape Verde, the Azores, and the Galápagos, and projected the data into principal component space. The analysis revealed that volcanoes in the early, high-flux stage of island evolution, such as La Palma, El Hierro, Fogo, and Pico, commonly preserve clinopyroxene compositions consistent with recycling of evolved mush in their mafic lavas. Mature islands with waning magma flux, such as Tenerife and Gran Canaria, lack this signature in their mafic rocks, suggesting that as a volcanic system ages and its magma supply declines, the deep evolved mush solidifies between recharge events and its record is erased.

The implications for hazard assessment are significant. Because a large share of magma evolution at low-flux ocean island volcanoes occurs at depths of 18 to 25 kilometers or deeper, much of the pre-eruptive process may be poorly resolved by conventional geophysical monitoring, which is most sensitive to shallower crustal signals. The 2021 Tajogaite eruption did produce deep seismicity at 20 to 25 kilometers in the days before magma broke the surface, and the new petrological evidence suggests that such deep signals may mark the critical moment when basanitic recharge begins to evacuate the mantle mush. Recognizing that evolved, potentially more explosive melts can be generated and stored near the Moho without prolonged shallow accumulation, and that their mobilization may precede eruptions by only days to weeks, gives monitoring networks a clearer target: the deep, hidden reservoirs where La Palma’s eruptions, and perhaps those of many ocean island volcanoes, truly begin.

Subject of Research: Magma storage and mush evacuation in the ocean island volcano La Palma revealed by clinopyroxene chemistry

Article Title: Recurrent evacuation of mantle mush in ocean islands revealed by clinopyroxene from La Palma

Article References: Caracciolo, A., Ubide, T., Ágreda-López, M., Herrera, R., Marquez, A., González-García, D., Huertas, M. J., Ancochea, E., Chicharro, N., Coello-Bravo, J. J., & Petrelli, M. (2026). Recurrent evacuation of mantle mush in ocean islands revealed by clinopyroxene from La Palma. Nature Communications, 17(1), Article 9362. https://doi.org/10.1038/s41467-026-77213-9

Image Credits: AI Generated

DOI: 10.1038/s41467-026-77213-9

Keywords: La Palma, Cumbre Vieja, clinopyroxene, crystal mush, magma recharge, thermobarometry, ocean island basalt, phonolite, Canary Islands, volcanology, Tajogaite eruption, magma plumbing system

The size of the particles an eruption produces is not a trivial detail. It is the single most important factor controlling how far pyroclasts travel, how long they remain aloft, and what hazards they pose once they land. Coarse bombs and lapilli fall close to the vent, while fine ash can drift for hundreds or thousands of kilometers, fouling jet engines, coating crops, and settling into water supplies. Yet despite decades of study, volcanologists have lacked a complete picture of exactly how and where these particles form inside and around an erupting volcano. A new study published in Geology, led by Jacopo Taddeucci, a volcanologist at Italy’s Istituto Nazionale di Geofisica e Vulcanologia, now offers the most detailed microtextural evidence yet that the answer is far more complicated than simplified eruption models have assumed.

The stakes are easy to underestimate. As Taddeucci explains, volcanic ash and larger pyroclasts interfere with nearly every aspect of life downwind of an eruption. They disrupt air traffic and road traffic, and once the eruption is over the work has only begun: the material must be removed, and its effects on crops, plants, vegetation in general, and wildlife must be assessed. Understanding how these particles are formed, he argues, is essential precisely because the formation process controls their features—their size, shape, density, and ultimately their behavior in the atmosphere and on the ground.

To interrogate that process, the research team turned to techniques more often associated with materials science than with volcanology. Using scanning electron microscopy and X-ray microtomography, they analyzed pyroclasts collected from three mafic, or basaltic, volcanoes: Etna and Stromboli in Italy, and Cumbre Vieja in Spain. These instruments allowed the researchers to peer inside individual particles at microscopic scales, resolving features far too small to see with the naked eye but large enough to record the physical history of the magma that produced them. Scanning electron microscopy reveals surface textures and fine-scale fractures, while X-ray microtomography builds three-dimensional images of a particle’s interior without cutting it open, preserving the spatial relationships between crystals, voids, and welded fragments.

What the team found inside these particles was a record of violence and repair. By identifying and quantifying characteristic microtextures—including broken crystals, sutures, and incorporated clasts—the researchers demonstrated that fragmentation does not occur at a single depth and a single moment, as many simplified eruption models assume. Instead, the process is protracted, unfolding across several distinct stages. As Taddeucci puts it, this is not a process occurring at a single point in space and time; it covers a span of time and a span of spaces that reaches from inside the volcano to outside it. The particles that rain down on cities like Catania are, in effect, archives of a prolonged sequence of breaking and healing events that began deep within the plumbing system.

Some of this protracted behavior had already been documented in the open air. Volcanologists have long observed bombs and lapilli breaking apart in flight, shattering into smaller fragments as they arc away from the vent. What has remained invisible is everything that happens before the magma exits the volcano, where direct observation is impossible. The new study provides the first microtextural evidence that fragmentation is also protracted inside a volcano, extending the known sequence of breaking events from the observable exterior into the hidden interior of the edifice. The microscopic scars preserved in pyroclasts—fractured crystals, sutured contacts, embedded fragments of earlier generations of magma—now serve as a proxy for processes no camera can reach.

Perhaps the most consequential finding concerns the opposite of breaking. The team showed that crack healing and the welding together of pyroclasts can be just as important as fragmentation in controlling the final particle size distribution. Taddeucci notes that researchers are accumulating 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. In other words, an eruption’s ash output is not simply the residue of how thoroughly the magma shattered; it is the net result of a dynamic competition between fracturing and reassembly. Cracks can close, and fragments that separate can fuse back together, particularly in hot, low-viscosity basaltic systems where freshly exposed surfaces remain plastic enough to weld.

This reframing has direct implications for hazard modeling. Particle size governs how pyroclasts are dispersed through the atmosphere, and computer models of eruptions rely on assumptions about that size distribution to forecast ash cloud trajectories, ground deposition, and aviation impacts. If fragmentation is protracted and healing is significant, then models that treat fragmentation as a single instantaneous event at a fixed depth may systematically misestimate the grain size of the erupted material—and with it, the reach of the hazard. Incorporating the full break-and-heal history into eruption models could therefore sharpen forecasts of how far ash will travel and how long airports, roads, and agricultural areas will remain affected.

The microtextures identified in the study are not unique to the three volcanoes examined. Asked whether the same features would appear in material from Etna’s eruption this summer, Taddeucci did not hesitate: yes, of course, he says, adding that most basaltic eruptions that are explosive in nature will produce these kinds of features. That generality is what makes the finding powerful. Rather than a quirk of one volcano or one eruption, the break-and-heal signature appears to be a common feature of explosive basaltic volcanism worldwide, from the pulsing fountains of Stromboli to the sustained activity of Cumbre Vieja on La Palma.

There is also a retrospective dimension to the work. Because these microtextures can be preserved in rocks from past eruptions, researchers can use them to reconstruct the fragmentation conditions of events that occurred centuries or millennia ago, extending the observational record far beyond the era of modern monitoring. Taddeucci highlights this as a significant advantage volcanology holds over other geophysical hazards: unlike earthquakes, which leave no comparable physical archive of their internal dynamics, eruptions preserve a durable record of the conditions under which their products formed. Reading that record could improve models of future eruptions at well-studied volcanoes and at sites whose behavior is known only from ancient deposits. Taddeucci also emphasizes that the research depended on collaboration, comparing eruptions across different volcanoes and countries—a scope possible only through cooperation with colleagues at observatories and institutions, including researchers beyond the paper’s official list of co-authors. As ash clouds continue to test the resilience of aviation and communities, the microscopic scars inside volcanic particles are proving to be one of the most informative records science has of what really happens when magma comes apart.

Subject of Research: Microtextural evidence for protracted magma fragmentation and healing during basaltic explosive eruptions

Article Title: Scientists find microscopic evidence that magma repeatedly breaks and heals during eruptions

Article References: Scientists find microscopic evidence that magma repeatedly breaks and heals during eruptions. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: volcanology, pyroclasts, magma fragmentation, Mount Etna, Stromboli, Cumbre Vieja, scanning electron microscopy, X-ray microtomography, volcanic ash, basaltic eruptions, Geology journal, eruption modeling