Scientists have identified a heat-driven process inside magma that could help explain why volcanoes with similar characteristics sometimes erupt in very different ways.
An international research team led by The University of Manchester analyzed magma from the 2021 Tajogaite eruption on La Palma, Spain. The scientists found that “superheating,” which occurs when magma becomes hotter than the temperature at which crystals remain stable, can postpone crystal formation as the magma moves toward the surface.
Superheating Removes Crystal Seeds
The study, published in Nature Communications, found that intense heat can dissolve tiny existing crystals that normally act as “seeds” for the growth of new crystals.
Superheating also reorganizes the magma at a microscopic level, making its internal structure more uniform and less favorable for new crystals to develop. These changes can affect both the speed at which magma rises and the ease with which volcanic gases escape. Together, those factors can strongly influence whether an eruption produces dramatic lava fountains or a slower release of lava.
The results provide new insight into a long-running scientific question about how magma’s temperature history affects crystallization before and during an eruption.
Lead author, Dr. Barbara Bonechi, Research Associate at The University of Manchester, said: “The history of crystal and bubble growth can dramatically control how a magma erupts; in particular, as more crystals grow, they eventually have a dramatic effect on magma viscosity. Until now, we did not fully understand the dynamics of crystal growth for magmas that received an injection of superheat just before ascent. But using our exciting and newly developed X-ray transparent pressure vessel combined with synchrotron X-ray microtomography, we can actually observe these processes ‘in situ’.”
Recreating Volcanic Conditions in the Laboratory
To investigate the process, the researchers recreated conditions found inside a volcano using magma collected from the Tajogaite eruption. That magma may have been superheated before the eruption and while it was rising through the crust.
At Diamond Light Source, the team used synchrotron X-ray microtomography to watch crystals form inside the magma in real time. They also conducted complementary ex-situ experiments in Prague, which made it possible to observe the samples over longer periods.
Together, the experiments allowed the scientists to follow crystallization under carefully controlled conditions of intense heat and pressure.
Crystal Growth Delayed for More Than Eight Hours
The difference between the samples was striking. Magma that had not been superheated began forming crystals after about 20 minutes.
By comparison, strong superheating prevented crystal formation for more than eight hours.
The researchers used these experimentally measured nucleation delays in numerical models of magma ascent. These simulations were designed to show how magma moves and changes as it travels upward through Earth’s crust.
How Heat Can Change an Eruption
The models indicated that a long delay in crystallization can keep magma relatively fluid, allowing it to rise rapidly toward the surface. This fast-moving magma could help generate dramatic lava fountains.
When crystals begin forming earlier, however, the magma becomes thicker and more viscous. It then rises more slowly, giving volcanic gases additional time to escape and making a gentler, effusive eruption more likely.
The researchers say this newly recognized role of superheating could help volcanologists better interpret monitoring data and improve forecasts of eruption behavior.
Co-author Dr. Margherita Polacci, Senior Lecturer in Volcanology at The University of Manchester, said: “Current volcanic hazard models typically focus on magma chemistry, gas content and pressure changes. This work suggests that pre-eruptive thermal history and crystallization kinetics may also play an important role in controlling magma ascent and eruptive behavior, with implications for volcanic hazard assessment.”
