Press release: Magma in motion: when is an eruption triggered?

No. 56 - 31.03.2025

International research team analyses magmatic crystals formed prior to volcanic eruption 40,000 years ago

How long before the actual volcanic eruption are there warning signals deep down inside the Earth? An international research team led by the University of Göttingen has investigated this question by analysing volcanic deposits from a volcanic eruption that occurred in the Phlegraean Fields near Naples 40,000 years ago. The team found that fresh magma rising from depths caused the volcano to erupt within around 60 years. However, according to the researchers, this “warning time” – meaning the time until rising magma triggers an eruption – depends largely on the magma temperature. The results were published in the Bulletin of Volcanology.

During a massive volcanic eruption about 40,000 years ago, known as the Campanian Ignimbrite, around 300 cubic kilometres of magma were released. This makes it one of the largest and most explosive eruptions in Europe in the past 100,000 years. The processes that can trigger such a volcanic eruption are recorded in the “growth rings” of magmatic crystals. These crystals are found in the magma reservoir, an underground chamber where liquid magma collects under a volcano. Such crystals grow until shortly before an eruption. The researchers examined the crystals in the deposits from the Campanian Ignimbrite eruption using an electron microprobe, a device that bombards samples with electrons and measures their chemical composition along a profile with accuracy to a thousandth of a millimetre. This enabled the team to chemically analyse the final growth phase of the crystals shortly before an eruption.

“The distribution of the element barium along measured profiles at the crystal edge suggests that 40,000 years ago, a fresh supply of magma from the depths of the Earth triggered this massive eruption,” explains Professor Gerhard Wörner at Göttingen University’s Department of Geochemistry and Isotope Geology. “This proves, on the one hand, that this final magma supply occurred just before the eruption. Furthermore, mathematical modelling of the measured chemical profiles shows that this process caused the much older magma already present in the Earth's crust to erupt within just 60 years or so.”

However, the timing of the advance warning for such an eruption depends largely on the temperature of the magma, which cannot be determined with certainty. “If the temperature of the magma was higher than the assumed 900 degrees Celsius, the advance warning would be significantly shorter: at around 970 degrees Celsius, most estimates range from less than four years to just one month. If the temperature was lower, for instance around 850 degrees Celsius, the advance warning time could be between eight and 380 years,” says lead author Dr Raffaella Iovine, who conducted the study as part of her PhD research at Göttingen University and in collaboration with researchers from Naples.

Earthquake activity under the Phlegraean Fields, which has increased sharply in the last four years, has fuelled fears of a renewed eruption in the Naples region. The data now published provide the first indications of how long the re-awakened magmatic activity in the subsurface could take before an eruption. “However, our results do not indicate that an eruption will actually occur in the near future,” says Wörner. “Often, underground volcanoes become restless without a subsequent eruption on the Earth's surface. On the other hand, the volcanoes in the region of the Phlegraean Fields have been repeatedly active for over 300,000 years, often only a few hundred years apart.”

The Göttingen research work was funded by the German Research Foundation (DFG) and the German Academic Exchange Service (DAAD).

Original publication: Raffaella Silvia Iovine et al. Insights into magma reactivation times prior to a catastrophic highly explosive event: the Campanian Ignimbrite eruption (Campi Flegrei, Italy). Bulletin of Volcanology (2025). DOI: 10.1007/s00445-025-01812-5

Contact

Professor Gerhard Wörner

University of Göttingen

Department of Geochemistry and Isotope Geology

Goldschmidtstraße 1, 37077 Göttingen, Germany

Email: gwoerne@gwdg.de