The monitoring of radon emitted in the Campi Flegrei area over a long period offers new data for the evaluation of the real extent of the affected area from hydrothermal phenomena, also revealing itself as a potential indicator of the evolution of a volcanic crisis
With a study that lasted seven years, from 2011 to 2017, a team of researchers from the Department of Mathematics and Physics of the University of Campania "Luigi Vanvitelli", the National Institute of Geophysics and Volcanology (INGV) and the National Institute of Nuclear Physics (INFN) monitored the radon emitted in two sites of the Campi Flegrei caldera, the results of which have just been published in the journal Scientific Reports of Nature in the article 'Continuous radon monitoring during seven years of volcanic unrest at Campi Flegrei caldera (Italy)'.
In recent years, the interest of the international scientific community in the study of radon emissions as a tracer of natural endogenous phenomena (seismic and volcanic activity) has grown considerably. However, the radon signal monitored in soils is influenced by many environmental factors whose effects can be eliminated when recorded over a long period.
The scholars have taken into consideration the Campi Flegrei caldera which from 2004-2005 is characterized by ground uplift, seismicity, changes in the composition of fumarolic fluids and a general increase in the emission of volcanic-hydrothermal fluids.
Two measuring stations designed and built by INFN researchers were used to measure radon. As part of a collaboration with INGV, the two prototypes have been installed in Campi Flegrei in two sites 1 to 4 km away from the Solfatara and Pisciarelli areas, where the ongoing phenomenology is more evident. The instruments acquired automatically for a period of 7 years providing a unique set of radon data and environmental parameters.
"The acquired data were analyzed using innovative mathematical techniques aimed at extracting from the signal the part controlled by the endogenous processes”explains Fabrizio Ambrosino, mathematician of the University of Campania associated with INFN.
The results were then compared with the indicators of the hydrothermal activity of the caldera, including the seismic tremor generated by the Pisciarelli fumarole, the overall values of seismicity, the maximum vertical deformation of the ground acquired by the GPS networks during the current lifting. The long series of data show a strong correlation of radon with independent signals and the final results were of considerable interest.
"The data obtained from the study led us to evaluate that the area affected by the current phenomena is more extensive than the area in which seismicity occurs and where the main manifestations of hydrothermal activity are located, in Pisciarelli and Solfatara”says Flora Giudicepietro, INGV volcanologist and co-author of the study.
"In fact, the radon signals show variations over time that are well correlated with the more classic geophysical and geochemical parameters regularly monitored at Campi Flegrei" adds Giovanni Chiodini, INGV geochemist and co-author of the research.
“These results represent an absolute novelty in the study of the Flegrea caldera and mark a significant step forward in the use and interpretation of the radon signal, indicating how long time series, suitably filtered by the effects of environmental parameters, constitute an excellent additional tool in the monitoring of volcanic activity”, concludes Carlo Sabbarese physicist of the University of Campania associated with INFN, and first author of the research.
