Identified the "beating heart" of Etna from the study of lava fountains in 2015
A feeding system with two magmatic tanks, placed at different depths, identified as the mechanism behind the lava fountains that affected Etna in 2015
[Rome, 21 May 2021]
An operation similar to that of a beating heart, with a deeper magma tank that constantly feeds a more superficial one, where the gases pressurize giving rise to the burst of lava fountains: this is the result of the model developed for Etna by a team by researchers from the National Institute of Geophysics and Volcanology (INGV), just published in the scientific journal 'Applied Sciences'.
The study, entitled "Combining high-and low-rate geodetic data analysis for unveiling rapid magma transfer feeding a sequence of violent summit paroxysms at Etna in late 2015”, focused on a series of four lava fountains that affected the Voragine crater of the Sicilian volcano in December 2015.
The scientists analyzed the deformations of the volcano to trace the magma sources of the sequences of violent eruptions, to understand their dynamics and define the power system of Etna capable of producing such a rapid accumulation and violent release of magma.
“Our analysis of ground deformation data, obtained using high-frequency tilt and Global Navigation Satellite System (GNSS) data and DInSAR (Differential Interferometric Synthetic Aperture Radar) satellite imagery, covered a 12-day period encompassing the entire sequence eruption of December 2015”, explains Alessandro Bonforte, INGV researcher and first author of the article. “These measurements allowed us to define the complex interactions between the different storage areas in which the magma erupted with the paroxysms was temporarily stored".
The study made it possible to define the dynamics and transfer rates of magma from a deep magma chamber to a more superficial one. There the magma, rich in gas, stands temporarily accumulating pressure.
"The deep pressurized source supplies gas-rich magma to a more 'shallow' reservoir located at a depth of about 1,5/2 km,” Bonforte explains. “When the gas pressure exceeds the containment pressure of the rocks, a violent eruption occurs in the form of a paroxysm. This combined mechanism of two levels of 'storage' of magma at different depths therefore represents the possible 'engine' of such rapid and violent sequences of events”.
These paroxysms drain not only the magmatic material accumulated in the most superficial reservoir, but also part of what is stationed in the rest of the volcano's feeding system, with an eruptive rate of over 300 cubic meters per second. Conversely, when the gas pressure decreases, the paroxysm stops, let's say that the valve closes, and the deeper reservoir (located about 6 km deep) starts again to recharge the superficial one, as well as the blood flow in the heart which it is pumped from the atrium to the ventricle and then from the ventricle to the outside of the heart.
“The model we proposed, therefore, suggests a mechanism similar to that of a beating heart, in which a medium depth reservoir, at about 6 km, loads a more superficial reservoir, at about 2 km; this tank is located at a depth that allows the gas to separate from the rest of the melt, thus increasing the pressure, somewhat like when you see bubbles forming in a bottle of carbonated drink. Everything is silent until the pressure exerted by the gas present inside the magma is not too high, in essence the valve opens and paroxysm occurs, which drains the magma from the most superficial source and from the rest of the system, which is continuous. Once the excess pressure is released, the valve closes and the cycle begins again, with magma once again moving from the deep to the shallow reservoir. This mechanism could represent a valid conceptual model for events of a similar nature on Etna and other volcanoes around the world”, concludes Bonforte.
A systematic review ““Combining high- and low-rate geodetic data analysis for unveiling rapid magma transfer feeding a sequence of violent summit paroxysms at Etna in late 2015” was published in the journal 'Applied Sciences' (abstract at the bottom).
Link to the article: https://www.mdpi.com/2076-3417/11/10/4630
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Abstract
We propose a multi-temporal-scale analysis of ground deformation data using both high-rate tilt and GNSS measurements and the DInSAR and daily GNSS solutions in order to investigate a sequence of four paroxysmal episodes of the Voragine crater occurring in December 2015 at Mt. Etna (Italy). The analysis aimed at inferring the magma sources feeding a sequence of very violent eruptions, in order to understand the dynamics and to image the shallow feeding system of the volcano that enabled such a rapid magma accumulation and discharge. The high-rate data allowed us to constrain the sources responsible for the fast and violent dynamics of each paroxysm, while the cumulated deformation measured by DInSAR and daily GNSS solutions, over a period of 12 days encompassing the entire eruptive sequence, also showed the deeper part of the source involved in the considered period, where magma was stored. We defined the dynamics and rates of the magma transfer, with a middle-depth storage of gas-rich magma that charges, more or less continuously, a shallower level where magma stops temporarily, accumulating pressure due to the gas exsolution. This machine-gun-like mechanism could represent a general conceptual model for similar events at Etna and at all volcanoes.
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PRESS RELEASE
Identified the "beating heart" of Etna from the 2015 lava fountains
A feeding system with two magmatic reservoirs, located at different depths, identified as the mechanism underlying the lava fountain episodes occurred on Etna in 2015
[Rome, May 21, 2021]
An operation similar to a beating heart, with a deeper magma reservoir that constantly feeds a shallower one, where the gas pressurizes, giving rise to the burst of lava fountains: it is the result of the model developed for Etna by a team of researchers of the National Institute of Geophysics and Volcanology (INGV), just published in the scientific journal 'Applied Sciences'.
The study, entitled "Combining high-and low-rate geodetic data analysis for unveiling rapid magma transfer feeding a sequence of violent summit paroxysms at Etna in late 2015”, focused on a series of four lava fountains produced by the Voragine crater of the Sicilian volcano in December 2015.
Scientists analyzed the deformation of the volcano to trace the magmatic sources of the sequence of violent eruptions, in order to understand their dynamics and to define the feeding system of Etna capable of producing such a rapid accumulation and violent release of magma.
“Our analysis of the ground deformation data, obtained using high-rate tilt and GNSS (Global Navigation Satellite System) data and DInSAR (Differential Interferometric Synthetic Aperture Radar) satellite images, covered a period of 12 days encompassing the entire eruptive sequence in December 2015 ”, explains Alessandro Bonforte, INGV's researcher and first author of the article. “These measurements allowed us to define the complex interactions between the different storage volumes where the magma, erupted during the paroxysms, was temporarily stored”.
The study made it possible to define the dynamics and transfer rates of magma from a deep magma storage to a shallower one. There the magma, rich in gas, temporarily settles, building up pressure.
“The deeper storage supplies gas-rich magma to a more 'superficial' reservoir located at a depth of about 1.5 / 2 km”, explains Bonforte. “When the gas pressure exceeds a threshold pressure, a violent eruption occurs in the form of paroxysm. This combined mechanism of two levels of 'storage' of magma at different depths therefore represents the possible 'engine' of such rapid and violent sequences of events”.
These paroxysms drain not only the magma accumulated in the most superficial reservoir, but also part of the magma stationing in the rest of the volcano's feeding system, with an eruptive rate of more than 300 cubic meters per second. Conversely, when the gas pressure decreases, the paroxysm stops, let's say that the valve closes, and the deeper reservoir (located about 6 km deep) begins to refill the superficial one again, like the flow in the heart, pumping the blood from the atrium to the ventricle and then from the ventricle to outside the heart.
“The proposed model, therefore, suggests a mechanism similar to that of a beating heart, in which a medium depth storage, at about 6 km, feeds a shallower one, at about 1.5 / 2 km; this shallower reservoir is located at a depth that allows the gas to separate from the rest of the melt, thus increasing the pressure, like when you see bubbles forming in a bottle of a fizzy drink. Everything is quiet until the pressure exerted by the gas inside the magma is too high, essentially the valve opens and paroxysm occurs, draining the magma from the most superficial tank and from the rest of the system, which is continuous. Once the excess pressure has been released, the valve closes and the cycle begins again, with the magma starting again to move from the deep reservoir to the superficial one. This mechanism could represent a valid conceptual model for events of a similar nature on Etna and on other volcanoes in the world”, concludes Bonforte.
The work Combining high-and low-rate geodetic data analysis for unveiling rapid magma transfer feeding a sequence of violent summit paroxysms at Etna in late 2015 has just been published in 'Applied sciences
Figure 1 The variations in ground inclination in the tilt sensor traces record and clearly show the pulsations of the surface source with the impulsive emptying for each of the 4 lava fountains and the slow replenishment in the intervals
Figure 2 The integration of the various measurements (GNSS and satellite Radar) over the entire 12-day period highlights the rapid contraction of the building, due to the overall emptying of Etna's deepest supply system
Figure 3 Simplified scheme of the final model, with the deepest storage zone (the atrium), at 6 km, feeding the shallowest one (the ventricle) where the magma pressurizes to be erupted episodically as soon as the pressure exceeds the threshold