A crystal no wider than a human hair may hold clues to what happens just before a volcano erupts. In a study of rocks from the Central Andes, researchers found a shared chemical pattern in some of the tiniest plagioclase crystals, offering a new way to investigate how eruptions begin.
Plagioclase is a common white mineral found in volcanic rocks. It forms in magma a few kilometers below the surface, where it responds to changes in heat, water, and the mixture of materials in the magma. By studying individual crystals, scientists can look for details that whole-rock samples may blur together. Those details can record different stages in a volcano’s past, including the conditions shortly before an eruption.
Daniela Parra-Encalada, a Ph.D. candidate at the University of Queensland’s School of the Environment, led the analysis. Her team examined thin sections from 28 rocks representing seven volcanoes, along with rocks from two ancient super-eruptions. The samples came from a 230-kilometer stretch of the Central Andes in Chile and Argentina, and included volcanoes with different ages, eruption styles, and activity levels.
Under special microscopes, the researchers mapped the chemistry of tiny plagioclase crystals, known as microcrysts. They found that the smallest crystals across the Andean volcanoes shared the same chemical signature. These newest crystals, about the width of a human hair, formed during the final stages of an eruption. Parra-Encalada said every volcanic rock sample collected on the field trip carried evidence of the same process.
The team also compared its findings with studies from other parts of the Pacific Ring of Fire. Similar patterns in the smallest crystals there suggested that eruptions in those separate regions may have been set off by a common process. The researchers used computer modeling to connect the chemical signature to very hot magma rising from deeper underground and entering a shallower magma reservoir. That fresh heat and material can unsettle the volcano’s underground system, eventually helping trigger an eruption.
The researchers call the pattern the “plagioclase eruptibility field.” The name describes a promising clue, not a ready-made eruption forecast. More work is needed to learn whether the signature can reliably identify volcanoes that deserve closer monitoring. Senior author Terese Ubide, an associate professor, said the team plans to test whether the pattern appears in volcanoes formed in different settings, including oceanic volcanoes.
If the signal holds up across more volcanoes, crystal chemistry could add a useful line of evidence for scientists studying volcanic risk. The same crystals may also help researchers understand how magma systems gather valuable metals such as copper and gold, linking volcano research with the search for critical minerals. For now, the study shows that small mineral grains can preserve a surprisingly detailed record of forces moving deep beneath the surface.