Photomicrograph of a clinopyroxene crystal. This mineral formed in a magma chamber. Melt Inclusions (in black) are present in these crystals. (Credit: Corin Jorgenson, University of Strathclyde)
More than 800 million people live near an active volcano. Some of these volcanoes still defy existing models, making the exact prediction of their eruptions impossible. This is the case for Colli Albani in Italy which has produced major explosions in the past despite its magma being normally associated with mild effusive eruptions. An international team led by the University of Geneva (UNIGE) and including researchers from DESY and Helmholtz-Zentrum Hereon is shedding light on this mystery using an innovative approach: analysing crystals that retain traces of the last eruption using PETRA III. Published in the Journal of Petrology, this study paves the way for new analytical methods in volcanology and strengthens hazard mitigation.
Monitoring volcanoes to anticipate their potentially devastating effects requires a detailed understanding of the signals that precede an eruption. However, this task becomes challenging when a volcano defies predictive models—such as Colli Albani, located just 20 kilometres from Rome. In theory, its magmatic composition should result in low-intensity eruptions. Yet, its past eruptions tell a different story.
Magma contains volatiles (mainly water and carbon dioxide), like opening the cap of a bottle of soda, when the magma rises toward the surface, it releases the volatiles, and the more viscous the magma, the more difficult it is for the gas to escape. The retention of gas results in a progressive increase of pressure which eventually leads to violent explosive eruptions. In theory, Colli Albani should not pose this risk as its magma is not very viscous. Yet, it has produced several violent and large volume explosive eruptions, the most recent occurring 355,000 years ago, when it spewed up to 30 km³ of scorching ash and molten rock into the atmosphere.
To learn more, the research team analysed ‘‘melt inclusions’’ from the magma of the last eruption with the help of synchrotron radiation. These tiny droplets of magma, measuring just one-hundredth of a millimetre, were sealed inside crystals before the explosion, preserving valuable clues about the magma’s chemistry, its water and carbon dioxide content—key factors in its explosiveness—as well as its temperature and pressure. In total, the researchers studied 35 crystals containing 2,000 inclusions.
An Innovative Approach to Probing Magma
Scientists from UNIGE collaborated with several institutions, including DESY, the University of Rome Tre, the University of Bristol and the Helmholtz-Zentrum Hereon. Using PETRA III, the team was able to obtain high-resolution 3D X-ray images of magma inclusions.
“This approach is innovative in volcanology, particularly in the study of melt inclusions. It opens up new perspectives in the field,” explains Corin Jorgenson, first author of the study and a doctoral student at the Department of Earth Sciences of the UNIGE Faculty of Science at the time of the research, now a postdoctoral researcher at the University of Strathclyde in Scotland.
Valuable Results for Risk Prevention
One of the major discoveries was the presence of numerous large-volume bubbles of water and carbon dioxide within the inclusions. This indicates that, when they were trapped, the Colli Albani reservoir already contained significant amounts of gas. “The excess gas made the magma similar to a sponge, compressed when additional magma accumulated in the reservoir, and rapidly expanding at the onset of eruption, both essential ingredients for the unexpectedly large and highly explosive eruption of Colli Albani,” explains Luca Caricchi, professor of Petrology and Volcanology at the Department of Earth Sciences of the UNIGE Faculty of Science, who led the research.
These results shed light on the mechanism behind the Colli Albani eruptions and highlight the importance of 3D imaging techniques in volcanology using synchrotron radiation. This approach, applicable to other volcanoes, will deepen our understanding of magma storage and degassing while improving volcanic hazard mitigation.
“What is particularly nice about this work is the truly interdisciplinary and international collaboration,” says Michael Stückelberger, scientist at DESY and co-author of the study. “There were also challenges, such as the huge amount of data. In this sense, this study is also methodologically groundbreaking: While traditionally single-case studies are often carried out at synchrotrons, the massive increase in throughput makes new scientific fields of geology, biology and also materials science accessible, where statistical significance requires the measurement of many samples.”
(from DESY News)
Reference:
C Jorgenson, M Stückelberger, G Fevola et al., A Myriad of Melt Inclusions: A 3D Analysis of Melt Inclusions Reveals the Gas-Rich Magma Reservoir of Colli Albani Volcano (Italy), Journal of Petrology (2025), DOI:10.1093/petrology/egaf012
