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A small international team of volcanologists has built a more detailed picture of the Campi Flegrei caldera's internal structure using high-resolution seismic imaging and results from rock physics experiments conducted on core samples collected from deep wells.

In their study in the journal Nature Communications, the group reconstructed the fine-scale structure of the Campi Flegrei caldera down to a 250 m grid size, and studied physics experiments to provide a more realistic image of the true nature of the caldera and any threats it may pose.

The Campi Flegrei caldera, which is part of the Phlegraean Fields, is a large caldera situated west of Naples, Italy. Prior research has shown that it has a long and active history. Its last major eruption was approximately 109,000 years ago, and it was massive, accounting for much of the makeup of the caldera, which is roughly 15 km wide.

A less-forceful eruption occurred in 1538—recent enough that evidence provided by locals survives. Many reported that significant ground uplift had occurred leading up to the eruption. Over the past 75 years, researchers have noted episodic uplift, suggesting another eruption may be imminent.

To find out if that might be the case, the research team conducted a deep and thorough analysis of the caldera to learn more about its underground structure.

In analyzing their high-resolution imaging and data from physics experiments that have been conducted on core samples over time by various researchers, the research team discovered that the caldera is made up of three layers.

They describe the top layer as fibrous caprock, made of volcanic products and approximately 1 to 2 kilometers deep. As its name implies, it serves as a cap on top of the caldera. The next layer down is a steam-filled chamber with water pooling at the bottom—it extends down 2 to 4 kilometers. Below that, they found what they describe as the caldera's basement—a dense rock formation that the research team suggests serves as the backbone of the caldera.

In their work, the researchers found no evidence of a magma buildup, suggesting an eruption any time soon appears unlikely. Instead, blasts of steam will likely occasionally make their way to the surface as pressure builds in the steam chamber, perhaps at times allowing the uplift to recede.

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