New technology to provide better monitoring of the Campi Flegrei supervolcano

Seismic noise provides information on the inner structure of the volcano near Naples

17 July 2019

The Phlegraean Fields – or Campi Flegrei in native Italian – is one of the most dangerous sites in Europe. This caldera region near Naples was formed some 40,000 years ago by the eruption of a supervolcano. Today several hundred thousand people live in the nearby coastal strip alongside the Mediterranean and, thus, in the immediate vicinity of the volcano. The Campi Flegrei area experienced innumerable micro-earthquakes in 1983 and 1984. Since then, things have been suspiciously quiet. "This apparent tranquility might be deceptive," as Professor Luca De Siena pointed out. "We do not know exactly what is actually going on inside this supervolcano." De Siena is a volcanologist and himself grew up in Naples. In March 2019, he transferred from the University of Aberdeen in Scotland to Johannes Gutenberg University Mainz (JGU), where he now heads the Volcano Seismology group at the Institute of Geosciences.

Analyzing occurrences in a volcano using seismic methods is only possible when related earthquakes can be measured. As there have been no such tremors for roughly 35 years, very little is known about the current status of the subterranean structure of this volcano. The Phlegraean Fields are situated just 20 kilometers to the west of Vesuvius and it is assumed that the two share a common magma chamber. Using a technique that is relatively new in seismology, De Siena has managed to identify the route taken by the molten materials that supply the Campi Flegrei supervolcano. "This new method allows us to look inside the volcanic system and obtain a better picture of its interior." The corresponding images are generated by sounds known as seismic noise, a kind of vibration that in this case occurs when waves break on the coast near Campi Flegrei. "The noises tell us the way the volcano is breathing." De Siena has located a channel that links lower sources of magma, probably active since the 1980s, with the upper sections of the volcano, and through which molten rock is fed into the hydrothermal system. Toxic gases flow from this main channel to the Solfatara and Pisciarelli fumeroles.

Internal structure of the caldera mapped for the first time since the earthquakes of the early 1980s

"We are now able to better understand how magma and other molten materials reach the surface from the depths of the volcano," explained De Siena, who had the opportunity to become familiar with the new technique during a research stay in Tokyo. It involves the use of a seismometer that records the very low frequency signals that are generated by the interaction of sea waves with the volcanic rock. "In effect, this enables us, in a manner of speaking, to x-ray the volcano."

One of the future applications of this recently tested technology will be its use to monitor volcanic activity in the area and, for this purpose, De Siena will be collaborating with the National Institute of Geophysics and Volcanology (INGV) in Naples. While the recording of seismic noise is a technique widely used by researchers, this is the first time it has been employed in a densely populated region like that around the Phlegraean Fields. The last major eruption here occurred nearly 500 years ago, creating a new volcanic cone with a height of more than 100 meters. "The whole area is like a powder keg waiting to go off. But once we comprehend in more detail the character of the volcano, we should be able to improve our monitoring of it so that we can give the local population a sufficiently early warning in emergencies," said De Siena. He and other geoscientists at JGU will continue to work on enhancing their ability to do this in future.