According to a study, the Under the caldera of Campi Flegrei, at a depth of about 2 kilometers, there is a cylindrical volume of rock – 500 meters high and about 5 kilometers in diameter – which is playing an important role in the uplift phase of the area.
This is suggested by a study published in the “Journal of Volcanology and Geothermal Research” and carried out by scholars from the University of Bologna and the National Institute of Geophysics and Volcanology.
“This source of deformation was already known to have contributed to the ground uplift that occurred in the Campi Flegrei area between 1982 and 1984,” explains Massimo Nespoli, researcher at the Department of Physics and Astronomy “Augusto Righi” of the University of Bologna and first author of the study.
“The results of our investigation show how the time series of ground uplift observed over the last 18 years can be reproduced by assuming the reactivation of that same deformation source, located at about 2 kilometers depth”.
In these episodes of uplift – the researchers suggest – the role of the movement of magma would therefore be secondary to that of hot and pressurized fluids that move within the rocks of the hydrothermal system of the caldera.
“Even if the magmatic contribution cannot be excluded – adds Nespoli -, the results obtained with the physical modeling of this source of deformation, linked to the arrival of hot and pressurized fluids, allow to effectively explain both the rate of uplift and the trend of seismicity, without the need to invoke the ascent of magma in the superficial layers of the Campi Flegrei caldera”.
The Campi Flegrei caldera, west of the city of Naples, is one of the most populated volcanic areas in the world. It is believed – Unibo informs – that volcanic activity has been present in this area for at least 47 thousand years.
The two main eruptive episodes, which shaped the Gulf of Pozzuoli as we know it today, occurred approximately 39 thousand and 15 thousand years ago, while the last eruption occurred in 1538. Starting from the middle of the last century, the caldera then underwent several episodes of uplift and lowering of the ground, known as "bradyseism".
In recent decades there have been two major phases of ground uplift: between 1969 and 1972 and between 1982 and 1984. During this last bradyseismic crisis, the maximum ground uplift – measured in Pozzuoli – was almost 1,8 meters, and was accompanied by more than 16 thousand low-magnitude earthquakes.
After 1984, the Campi Flegrei caldera experienced a subsidence phase that lasted twenty years, interrupted every now and then by small and brief episodes of uplift. Until 2000, when the rate of subsidence slightly reversed.
While since 2005 a new phase of ground uplift has begun, with a progressive increase in the rate of seismicity, especially below the Solfatara crater: an area about 3 kilometers from the center of Pozzuoli, known for its fumaroles, high-temperature gas emissions.
To investigate the causes of the current phase, researchers have hypothesized a comparison with the previous bradyseismic crisis, the one between 1982 and 1984. The study of that phenomenon has in fact shown that a significant contribution to the large and rapid uplift of the ground had been made by a cylindrical volume of rock located at a depth of about 2 kilometers.
This volume of rock had been crossed by hot and high-pressure fluids exhaled from a deep magma chamber. And because of the high temperatures and strong pressures it had expanded: a dilation that had deformed the surrounding space, causing both the uplift of the ground and the earthquakes.
New analyses carried out by scholars have now shown that the reactivation of that same deformation source could also explain the ground uplift phenomena observed in recent years.
“The presence of this deformation source had been highlighted in the past by seismic tomography studies: further confirmation now comes from the observation of a sharp variation in the ratio between the number of earthquakes with small magnitude and the number of earthquakes with high magnitude”, confirms Nespoli.
“The low value of this parameter within the deformation source is in fact consistent with the fact that earthquakes with greater magnitude are mainly favored and induced within and nearby the same deformation source responsible for the ground uplift”.
Article published on November 8, 2023 - 14:27
