Campi Flegrei: Italy's active supervolcano rose 66 feet in last eruption

Researchers studied a unique dataset, including geological, archaeological, and historical data, to understand the events surrounding the 1538 eruption— the only historically analyzable eruption of the Phlegraean caldera. They analyzed ground-level changes along the coast from 1515 to 1650.

"It emerged that the eruption was preceded by an intense deformation of the ground which first concerned the area of ​​Pozzuoli, then localized in the area of ​​the future eruptive vent, reaching an elevation of 20 meters," said first author Elisa Trasatti, a researcher at the National Institute of Geophysics and Volcanology (INGV), in a press release.

Their models also showed magma transfer during the eruption from a 4 km deep source to the Monte Nuovo vent. In the subsequent period, soil uplift occurred without eruption—Mauro Antonio Di Vito, co-author and director of INGV Vesuvius Observatory explained his team called this phenomenon an 'aborted eruption.' 

What happens when Campi Flegrei erupts? 

According to an article by LiveScience, a hypothetical replication of Campi Flegrei's largest documented eruption 39,000 years ago would eject molten rock and volcanic gases into the stratosphere, generating tsunamis up to 100 feet (33.5 meters) tall. 

The eruption would also release sulfur and toxic ash plume, potentially inducing a years-long global winter, leading to crop failures and mass extinctions.

However, the researchers uncovered that eruptions from Campi Flegrei can fizzle out without the volcano unleashing its full destructive power. 

"It has been estimated that the portion of magma erupted in 1538 is about one-hundredth of that which accumulated under the volcano between 1250 and 1650," explained Valerio Acocella, professor at the Roma Tre University and co-author of the research. 

"This fact highlights the strong capacity of the Phlegrean system to retain the magma, erupting a minimal portion." 

The complete study was published in Geophysical Research Letters on June 16 and can be found here.

Study abstract:

Shallow magma transfer is difficult to detect at poorly monitored volcanoes. Magma transfer before the last 1538 eruption at Campi Flegrei caldera (Italy) was exceptionally tracked using historical, archeological, and geological data. Here, we extend that data set to 1650 to uncover any magma transfer during post-eruptive subsidence. Results show two post-eruptive subsidence phases, separated by a previously undocumented uplift during 1540–1582. Uplift highlights the pressurization of the central (∼3.5 km depth) and peripheral (∼1 km depth) pre-eruptive sources, suggesting an aborted eruption. The subsidence events mainly require the depressurization of the central source and pressurization of a deeper magmatic layer (∼8 km depth). Therefore, despite the overall post-eruptive deflation, after 1538 the deeper reservoir experienced continuous magma supply, with magma almost erupting between 1540 and 1582, challenging the common assumption of post-eruptive deflation. This underlies the importance of monitoring the deeper magmatic systems, also after eruptions, to properly assess their eruptive potential.