Understanding the Campi Flegrei supervolcano: Rupture risks and eruption uncertainties

A new in-depth study reveals the potential eruption risk at Italy’s Campi Flegrei, also known as the ‘supervolcano’, has increased. The research, published on June 9, 2023, shows that the volcano has been showing signs of increased activity, raising both concerns and interest among scientists.

• As per a study published on June 9, 2023, researchers from University College London (UCL) and Italy’s National Research Institute for Geophysics and Volcanology (INGV) predicted in 2016 that the approach to rupture would continue after an additional uplift of 30 – 40 cm (11.8 – 15.7 inches) at the location of largest movement.
• The researchers have now updated their analysis with new data on changes in the numbers of local earthquakes with amounts of ground movement and showed that subsequent events have confirmed their prediction and that the unrest has been changing the structure of Campi Flegrei’s crust. The results provide new constraints for evaluating the volcano’s potential to erupt or to subside without eruption.

The Campi Flegrei, located near Naples in southern Italy, has a crust that is weakening and becoming more prone to rupturing, making an eruption increasingly likely. If the volcano erupts, it would be its eruption since 1538.

Over 1.5 million people live above this vast underground volcano complex, with half a million residing within its 11.3 km (7-mile) long caldera, which was formed after an enormous eruption 39 000 years ago.

If Campi Flegrei were to repeat its most significant previous eruption, it could cause severe environmental damage. The eruption would expel molten rock and volcanic gases high into the stratosphere, potentially causing 30 m (100 feet) high tsunamis. A plume of sulfur and toxic ash could spread across the globe, potentially causing a global winter for several years, leading to crop failure and mass extinctions.

Though Campi Flegrei is often referred to as a supervolcano, this categorization is not yet definitive. Supervolcanoes are capable of producing eruptions of the highest magnitude, an 8 on the Volcano Explosivity Index, expelling more than 1 000 cubic kilometers (240 cubic miles) of material. However, Campi Flegrei’s most significant eruption to date ejected up to 285 cubic kilometers (70 cubic miles) of material, classifying it as a category 7 eruption. The eruption would also release hazardous chemical elements, such as fluorine, which in large amounts can be harmful to plants and animals.

The volcano has been showing increased activity since the mid-20^th century, with increased activity periods in the 1950s, 1970s, and 1980s. A period of unrest that began in the last decade is still ongoing. The town of Pozzuoli, located on the volcano’s roof, has seen an elevation change of 4 m (13 feet) since the 1950s, with the ground rising by 10 cm (4 inches) each year. Over 600 small earthquakes were detected in April, marking a record-breaking monthly total for the region.

The increased activity is likely caused by volcanic gas seeping into the crust 3 km (1.86 miles) beneath Campi Flegrei’s surface, causing it to stretch, warp, and slip, leading to the occurrence of earthquakes. If enough volcanic gas enters the crust, the heat and pressure it provides can push the rocks beyond their “critical degassing pressure,” rupturing them and opening up a pathway for the magma beneath to burst outwards in an eruption.

The research team combined seismic readings with measurements of ground uplift to estimate the changing tensile strength of the region’s crust (the maximum stress a material can take before breaking) and its proximity to rupture.¹

Their model suggests that the crust beneath Campi Flegrei is breaking and not bending under pressure. The underground gas and magma have been slowly flexing and weakening the volcano’s crust since the 1950s, reducing its tensile strength to just a third of what it was in 1984. This means that even though the earthquakes in the region are not as powerful as they were in the 1980s, the weaker rock has the potential to rupture under smaller strains, giving seismologists fewer detectable earthquakes and people less notice to evacuate.

However, the researchers caution that these findings do not guarantee a catastrophic eruption. For an eruption to occur, gases must build up faster than they can escape, and magma also needs to be able to move rapidly through the crust where a crack has formed. These conditions cannot be definitively known until an eruption takes place.

Despite these alarming findings, it’s important to remember that the future behavior of the volcano remains uncertain. “It’s the same for all volcanoes that have been quiet for generations. Campi Flegrei may settle into a new routine of gently rising and subsiding, as seen at similar volcanoes around the world, or simply return to rest. We can’t yet say for sure what will happen. The important point is to be prepared for all outcomes,” study co-author Dr. Stefano Carlino from the Vesuvius Observatory concludes.

Geological summary

Campi Flegrei is a 13 km (8 miles) wide caldera that encompasses part of Naples and extends to the south beneath the Gulf of Pozzuoli. Episodes of significant uplift and subsidence within the dominantly trachytic caldera have occurred since Roman times.

The earliest known eruptive products are dated 47 000 years BP. The caldera formed following two large explosive eruptions, the massive Campanian ignimbrite about 36 000 BP, and the over 40 km³ Neapolitan Yellow Tuff (NYT) about 15 000 BP.

Following the eruption of the NYT a large number of eruptions originated from widely scattered subaerial and submarine vents.

Most activity occurred during three intervals: 15 000 – 9 500, 8 600 – 8 200, and 4 800 – 3 800 BP. The latest eruption was in 1158 CE at Solfatara and activity in 1538 CE that formed the Monte Nuovo cinder cone.²

References:

¹ Potential for rupture before eruption at Campi Flegrei caldera, Southern Italy – Christopher R. J. Kilburn et al. – Nature – June 9, 2023 – DOI https://doi.org/10.1038/s43247-023-00842-1 – OPEN ACCESS

² Campi Flegrei – Geological summary – GVP

Featured image credit: Copernicus EU/Sentinel-2, EO Browser, The Watchers. Acquired on June 1, 2023