Developed a physical-mathematical model capable of explaining the mechanisms that regulate seismic and volcanic activity, through the measurement of the radon emitted by the soils of Etna. The study, carried out by a team of researchers from INGV and the Universities of Catania and the Azores, was recently published in Scientific Reports (Nature Publishing Group)
Understand the mechanisms that regulate seismic and volcanic activity through the measurement of radon emitted by the soils of Etna, one of the most active volcanoes in the world both in terms of frequency of eruptions and intensity of seismic and tectonic activity. This is the goal of a group of researchers from the National Institute of Geophysics and Volcanology (INGV) and the Universities of Catania and the Azores who have been exploring the potential of this gas for over ten years with a network of sensors. The research was recently published in Scientific Reports (Nature Publishing Group).
"We analyzed the radon emissions from Etna soils recorded in the period 2009-2011 by a sensor located in Piano Provenzana, about 1800 meters above sea level on the north-eastern flank of the volcano", explains Marco Neri, senior researcher at the INGV-Observatory Etna (INGV-OE). “This sector of Etna has the peculiarity of being both near a very active seismogenic fault and at the edge of the North-East Rift, which represents a volcano-tectonic structure physically connected to the central conduit of the volcano and which is of intense outgassing. A peculiarity of the site that makes the radon probe potentially sensitive both to earthquakes produced by the fault and to volcano eruptions".
As soon as the 2009 probe was installed, the fault originated an intense seismic swarm (April 2-3, 2010). A short time later, the volcano also generated three paroxysmal eruptions (from January to March 2011) which marked the beginning of the growth of a new, imposing pyroclastic summit cone, later christened the New Southeast Crater.
"Having, therefore, earthquakes and eruptions in a limited period of time and a radon probe strategically positioned to record these events, it was possible to acquire fundamental data to understand how radon varies during earthquakes and eruptions", he continues. Marco Neri.
The radon variations were statistically analysed, comparing them with the main meteorological parameters. The permeability of the soils, a characteristic that influences the release of the gas, in fact varies according to the rainy periods (the rainwater infiltrates the soil, occupying the interstitial voids and preventing the gas from escaping), causing variations in the measurement of radon . Similar effects also occur in the presence of snow and in periods of high atmospheric pressure, such as in summer. Hence the need to purify the radon signal from variations related to meteorological conditions.
"The analysis", adds the INGV-OE researcher, "revealed the existence of three periods of degassing considered anomalous from 2009 to 2011. The first, which began in February 2010, was characterized by low radon concentration values which preceded the earthquake swarm of 7-2 April 3 by about 2010 weeks. After the negative anomaly in February, radon increased steadily until it reached maximum values a couple of days before the earthquake swarm. A variation due to the progressive increase in soil permeability in correspondence with the fault plane that generated the seismic swarm. The other two periods concern positive anomalies (January and February 2011) characterized by very high values which occurred in conjunction with three paroxysmal eruptions of Etna. Also in this case, the weeks preceding the anomalies were characterized by the progressive increase in radon, but this time with decidedly greater oscillations, compatible with sudden variations in the speed of gas emissions, probably connected with volcanic activity".
To locate the source of this gas, the uranium content, from which radon is generated by radioactive decay, was analyzed in the lava of the volcano and in the rocks of its sedimentary base. The main source rock is located at a depth of 600-1400 m, from which radon rises to the surface at a rate exceeding 50 m/day.
“The study lays the groundwork for a deeper understanding of the tectonic and volcanic processes that cause variations in radon emissions, particularly in active basaltic volcanoes such as Etna. The results obtained stimulate us to continue these studies through a multidisciplinary approach integrated with the other INGV monitoring networks”, concludes Marco Neri.
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Figure 1 – Location of the radon probe (see yellow arrow) in Piano Provenzana (1800 m above sea level), a short distance from a seismogenic fault which on 2-3 April 2010 triggered an intense seismic swarm. The same fault borders the North-East Rift, a volcanic-tectonic structure connected with the central eruptive conduit of Etna and site of frequent lateral eruptions. Photo by M. Neri.
Figure 2 – Co-seismic faulting of the “Mareneve” road which occurred during the seismic swarm of 2-3 April 2010. The westernmost segment of this fault is a few tens of meters from the radon probe installed in Piano Provenzana. During the earthquake swarm, the radon probe recorded anomalous values starting a few weeks before the swarm. Photo by M. Neri.
Figure 3 - Paroxysmal eruption of the New Southeast Crater of Etna. Eruptive events of this type were analyzed in 2011 through the radon gas emissions recorded by the probe placed on the Piano Provenzana, on the high eastern flank of the volcano. Photo by M. Neri.
Figure 4 – Radon probe installed in Piano Provenzana (1800 m above sea level), north-eastern flank of Etna. The probe is located underground, about 2 meters deep, in a hole located inside the perimeter delimited by the yellow-black poles. In the background you can see the edge of the North-East Crater, which is the highest point of the volcano (3329 m). Photo by M. Neri