With very high precision instruments, micro deformations of the volcanic edifice were recorded in the period 2020-2021. By evaluating the data, the researchers identified the phase that anticipates the onset of the eruptive sequence and modeled the effects recorded during the lava fountain eruptive phase.
In the short period from 13 December 2020 to 31 March 2021, Etna erupted around 60 million cubic meters of magma mainly through particularly energetic lava fountains. Considering the volume of volcanic material accumulated over time and that erupted in the four months, it can be seen that lava fountains can represent an effective way of emitting magma capable of replacing the more dangerous and traditional effusive eruptions on the side of the volcano.
Furthermore, the detection of micro-deformation of the volcanic edifice has made it possible to identify precursory signals that anticipate the occurrence of an eruptive sequence. These are some of the results of the study Magma Migration at Shallower Levels and Lava Fountains Sequence as Revealed by Borehole Dilatometers on Etna Volcano edited by a team of researchers from the National Institute of Geophysics and Volcanology - INGV (A. Bonaccorso, G. Currenti, L. Carleo, A. Sicali) and recently published in the journal 'Frontiers in Earth Sciences'
“In open vent volcanoes like Etna”, explains Alessandro Bonaccorso, INGV volcanologist and first author of the study, “a major challenge is to detect and interpret even ultra-small energy variations associated with minor but critical events such as lava fountains. This objective is potentially achievable with extremely precise recordings of deformations (so-called "strain") induced in the volcanic edifice and detectable, even at distances of several kilometers from the crater area, by dilatometers installed in deep drilling hundreds of meters deep. In the four months considered, the INGV dilatometer network installed on Etna recorded precise variations”.
"In particular”, continues Bonaccorso, “micro variations, observed in correspondence with the seismic swarms that occurred in December 2020, made it possible to highlight the migration of magma to the surface which anticipated the start of the eruptive sequence. Furthermore, the signal from the dilatometers showed clear short-term strain micro-variations associated with the "recharges" that preceded the lava fountains and the subsequent fast decompressions produced by them".
"Subsequently”, continues the researcher “a numerical model of the most superficial source that generated the lava fountains of the South East Crater of Etna has been proposed. In this way we had confirmation that it is the same source located between 0 and 1 km below sea level that generated the lava fountain events of the period 2011-2013. This spring can be interpreted as a sort of valve connected to the deepest main reservoir, located between 6 and 8 km below sea level, which modulates the repeated sudden decompression capable of generating lava fountains".
"In the study", adds Bonaccorso "parameters were also evaluated which provide useful information for understanding the state of an explosive sequence with characteristics similar to that of February - March 2021. This in order to understand when the activity of an eruptive sequence, characterized by a frequent repetition of events explosives, is being phased out.”
"In the end”, concludes the researcher, “the datum of the dilatometric signal allowed the estimation of the total volumes erupted in the single fountains allowing, during a sequence, to follow the value accumulated over time by these close eruptive events. This element highlights how the balance between the accumulated material and the erupted material can also take place through sequences of numerous lava fountains which, therefore, represent an effective method of magma emission capable of replacing the more dangerous and traditional eruptions on the side of the volcano ”.
Link: https://doi.org/10.3389/feart.2021.740505
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Etna, micro-deformations monitoring to reveal the beginning of an eruptive sequence
By using very high precision instruments, micro deformations of the volcanic building were recorded in the period 2020-2021. By evaluating the data, the researchers identified the phase that anticipates the start of the eruptive sequence and modeled the effects recorded during the eruptive phase of lava fountains.
In the short period from 13 December 2020 to 31 March 2021, Etna erupted about 60 million cubic meters of magma, especially through particularly powerful lava fountains. Considering the volume of volcanic material accumulated over time and that erupted over four months, it can be seen that lava fountains can represent an effective mode of magma emission capable of replacing the more dangerous and traditional effusive eruptions on the volcano flanks.
Furthermore, the detection of micro deformations of the volcanic edifice allowed to create a numerical model capable of predicting the occurrence of an eruptive sequence.
These are some of the results of the study Magma Migration at Shallower Levels and Lava Fountains Sequence as Revealed by Borehole Dilatometers on Etna Volcano, conducted by a team of researchers from the Italian Istituto Nazionale di Geofisica e Vulcanologia (INGV) (authors A. Bonaccorso, G. Currenti, L. Carleo and A. Sicali) and recently published in the journal 'Frontiers in Earth Sciences'.
"In open conduct volcanoes like Etna", explains Alessandro Bonaccorso, INGV volcanologist and first author of the study, "an important challenge is to detect and interpret even ultra-small energy variations associated with minor but critical events such as lava fountains. This objective is potentially achievable with extremely precise recordings of the strain induced in the volcanic edifice and detectable, even at distances of several kilometers from the crater area, by dilatometers installed in deep drillings hundreds of meters deep.The network of INGV dilatometers installed on Etna has recorded precise changes"
"In particular", continues Bonaccorso, " micro variations, observed in correspondence with the seismic swarms that occurred in December 2020, allowed to highlight the migration of magma to the surface that anticipated the start of the eruptive sequence. Furthermore, the signal of the dilatometers showed clear micro-variations in stress in the short term associated with the "recharges" that preceded the lava fountains and the subsequent fast decompressions produced by them"
"Subsequently", continues the researcher, "a numerical model of the shallower source that originates the lava fountains of the South East Crater of Etna was proposed. In this way we have had confirmation that it is the same source located between 0 and 1 km below the sea level that generated the lava fountain events of the period 2011-2013. This source can be interpreted as a sort of valve connected to the deeper main reservoir, located between 6 and 8 km below sea level, which modulates the repeated abrupt decompression capable of generating the lava fountain”.
"In the study", Bonaccorso adds, "were also evaluated parameters that provide further information on the state of an explosive sequence with the characteristics of that of February - March 2021. This in order to understand when the activity of an eruptive sequence, characterized by a frequent repetition of explosive events is in the phase of attenuation”.
“Finally”, concludes the researcher, “the data of the dilatometric signal allowed the estimation of the total volumes erupted in the individual fountains allowing, during an eruptive sequence, to follow the cumulative value over time by these close eruptive events. This element highlights how the balance between the accumulated magma and the erupted one can also occur through sequences of numerous lava fountains which, therefore, represent an effective mode of magma emission capable of replacing the more dangerous and traditional effusive eruptions on the volcano flanks”.
Link: https://doi.org/10.3389/feart.2021.740505
Fig. 1 – a) Detail of the strain recorded during the earthquake swarm of 19 December 2020 that accompanied the final intrusion of magma and during the subsequent first lava fountains of 21-22 December 2020. b) Detail of the strain variations recorded during the lava fountaining sequence from February 16 to March 31, 2021.
Fig 1. - a) Detail of the strain recorded during the 19 December 2020 swarm accompanying the intrusion and during the following first lava fountains on 21-22 December 2020. B) Detail of the strain changes recorded during the lava fountains sequence from 16 February to 31 March 2021.
Fig. 2 - Lava fountain on March 12, 2021. Strain signal measured at the DRUV station installed in a borehole at a depth of 200 m, and at a distance of 10 km from the central craters.
Fig. 2 - Lava fountain of 12 March 2021. Strain signal measured at the DRUV station installed in a borehole at a depth of 200 m, and at a distance of 10 km from the central craters.
