Italy’s Solfatara crater lies in the Phlegraean Fields caldera, near Mount Vesuvius, the volcano that buried the city of Pompeii in 79 CE. The Phlegraean Fields caldera is located inside the metropolitan area of Naples, and it is one of the largest volcanic systems on Earth. This caldera is currently showing significant volcanic unrest, mainly located around the Solfatara volcano. The crater’s boiling, sulfurous mud pools and fumaroles indicate an intense volcanic activity, which many scientists view as a serious potential threat to the roughly 3 million inhabitants of this region.
Scientists have long struggled to track Solfatara’s activity because the interactions between the gases in magma, water, and steam within volcanoes are still poorly understood. Now, however, a 3-D map of the complex water and gas-bearing tunnels and chambers within the caldera could aid that effort.
Gresse et al. used electrical resistivity tomography (ERT), a technique commonly used to study aquifers and other underground structures, to map the structure of Solfatara’s inner cracks and chambers. In ERT, researchers induce an electrical current between multiple electrodes placed on the ground and then collect profiles of the resistance it encounters as it passes through substances such as water, rock, mud, or gas. After doing this repeatedly, they can compile a 3-D picture of what lies below.
This study reveals, for the first time, the structure of a gas-filled reservoir 50 meters below the surface of the Solfatara caldera. It shows that the reservoir is attached to a 10-meter-thick channel that turns into an opening known as the Bocca Grande fumarole, a vent through which foul-smelling volcanic gases escape to the surface. It also reveals the hidden condensate water channels beneath the surface, as well as the precise dimensions of features such as the cryptodome, a body of magma that can make the surface of a volcano bulge without erupting.
Solfatara releases thousands of tons of hot carbon dioxide and water through vents such as the Bocca Grande fumarole every day. As pressure within the volcano builds over time, the ground above often rises and can cut off or change the shape of these internal release valves. Although the Phlegraean Fields caldera hasn’t erupted since 1538 CE, three ground uplift events have occurred since the 1950s, suggesting to some that the next eruption could be coming soon. (Journal of Geophysical Research: Solid Earth, https://doi.org/10.1002/2017JB014389, 2017)
—Emily Underwood, Freelance Writer