Explosive Paroxysmal Events at Etna Volcano of Different Magnitude and Intensity Explored through a Multidisciplinary Monitoring System

Between 13 December 2020 and 21 February 2022, Etna volcano produced a sequence of
66 paroxysmal explosive eruptions, with Strombolian activity at the summit craters climaxing in
lava fountains and eruption columns extending several kilometers above the craters, accompanied
by minor and short-lasting lava flows from the crater rim. We selected three of these episodes that
occurred within a short space of time, between 13 December 2020 and 12 March 2021, of different
magnitude (i.e., erupted volume) and intensity (i.e., mass eruption rate or instantaneous eruption
rate), and analyzed them from a multidisciplinary perspective. The aim was to gain insights into
those parameters that mostly reveal the eruptive process for hazard assessment purposes. The multidisciplinary
data consist of calibrated visible images, thermal images, seismic and infrasound data,
ground deformation detected from the strainmeters, as well as satellite SEVIRI images. From these
data, we obtained the timing of each paroxysmal event, the erupted volume in terms of tephra and
lava flows, and the corresponding deflation of the source region, together with the development of
the lava fountains and eruption columns with time. The results enabled determining that the smallest
episode was that of 13 December 2020, which comprised three distinctive pulses but did not
produce an eruptive column detectable from either monitoring cameras or satellites. The 28 February
2021 episode was remarkable for the short amount of time required to reach the climax, and was
the most intense, whereas the 12 March 2021 event showed the longest duration but with an intensity
between that of the previous two. Our results show that these three paroxysmal events display
a typical trend, with the first event also being the smallest in terms of both erupted volume and
intensity, the second being the most intense, and the third the one of greatest magnitude but less
intense than the second. This is coherent with the end of the first paroxysmal phase on 1 April 2021,
which was followed by 48 days of eruptive pause before starting again. In this context, the end of
the paroxysmal phase was anticipated by a more effusive episode, thus heralding a temporary decline
in the gas content within the feeding magma batch.

This research was funded by the Project FIRST-ForecastIng eRuptive activity at Stromboli
volcano: Timing, eruptive style, size, intensity, and duration; INGV-Progetto Strategico Dipartimento
Vulcani 2019 (Delibera n. 144/2020). A.C. thanks the CHANCE project, II Edition, Università
degli Studi di Catania (principal investigator A.C.) and the grant PIACERI, 2020-22 programme
(PAROSSISMA project, code 22722132140; principal investigator Marco Viccaro). A.I. thanks the
IMPACT project—A Multidisciplinary Insight on the Kinematics and Dynamics of Magmatic Processes
at Mt. Etna Aimed at Identifying Rrecursor Phenomena and Developing Early Warning Systems,
funded by INGV-Progetto Strategico Dipartimento Vulcani 2019 (Delibera n. 144/2020). S.S.
thanks the ‘e-shape’ project, which receives funding from the European Union’s Horizon 2020 research
and innovation programme under grant agreement 820852.

1. Alparone, S.; Andronico, D.; Sgroi, T.; Ferrari, F.; Lodato, L.; Reitano, D. Alert system to mitigate tephra fallout hazards at Mt.
Etna Volcano, Italy. Nat. Hazards 2007, 43, 333–350. https://doi.org/10.1007/s11069-007-9120-7.
2. Calvari, S.; Salerno, G.G.; Spampinato, L.; Gouhier, M.; La Spina, A.; Pecora, E.; Harris, A.J.L.; Labazuy, P.; Biale, E.; Boschi, E.
An unloading foam model to constrain Etna's 11–13 January 2011 lava fountaining episode. J. Geophys. Res. Earth Surf. 2011, 116.
https://doi.org/10.1029/2011jb008407.
3. Calvari, S.; Cannavò, F.; Bonaccorso, A.; Spampinato, L.; Pellegrino, A.G. Paroxysmal Explosions, Lava Fountains and Ash
Plumes at Etna Volcano: Eruptive Processes and Hazard Implications. Front. Earth Sci. 2018, 6, 107.
https://doi.org/10.3389/feart.2018.0010.7.
4. Calvari, S.; Bonaccorso, A.; Ganci, G. Anatomy of a Paroxysmal Lava Fountain at Etna Volcano: The Case of the 12 March 2021,
Episode. Remote Sens. 2021, 13, 3052. https:// doi.org/10.3390/rs13153052.
5. Andronico, D.; Corsaro, R.A. Lava fountains during the episodic eruption of South–East Crater (Mt. Etna), 2000: Insights into
magma-gas dynamics within the shallow volcano plumbing system. Bull. Volcanol. 2011, 73, 1165–1178.
https://doi.org/10.1007/s00445-011-0467-y.
6. Viccaro, M.; Garozzo, I.; Cannata, A.; Di Grazia, G.; Gresta, S. Gas burst vs. gas-rich magma recharge: A multidisciplinary study
to reveal factors controlling triggering of the recent paroxysmal eruptions at Mt. Etna. J. Volc. Geoth. Res. 2014, 278–279, 1–13.
7. Andronico, D.; Cannata, A.; Di Grazia, G.; Ferrari, F. The 1986–2021 paroxysmal episodes at the summit craters of Mt. Etna:
Insights into volcano dynamics and hazard. Earth-Sci. Rev. 2021, 220, 103686.
8. Calvari, S.; Nunnari, G. Comparison between Automated and Manual Detection of Lava Fountains from Fixed Monitoring
Thermal Cameras at Etna Volcano, Italy. Remote Sens. 2022, 14, 2392. https://doi.org/10.3390/rs14102392.
9. Scollo, S.; Coltelli, M.; Bonadonna, C.; Del Carlo, P. Tephra hazard assessment at Mt. Etna (Italy). Nat. Hazards Earth Syst. Sci.
2013, 13, 1–13.
10. Andronico, D.; Del Carlo, P. PM10 measurements in urban settlements after lava fountain episodes at Mt. Etna, Italy: Pilot test
to assess volcanic ash hazard to human health. Nat. Hazards Earth Syst. Sci. 2016, 16, 29–40. Available online: www.nat-hazardsearth-syst-sci.net/16/29/2016/ (accessed on 1 January 2022). https://doi.org/10.5194/nhess-16-29-2016
11. Horwell, C.J.; Sargent, P.; Andronico, D.; Lo Castro, M.D.; Tomatis, M.; Hillman, S.E.; Michnowicz, S.A.K.; Fubini, B. The ironcatalysed surface reactivity and health-pertinent physical characteristics of explosive volcanic ash from Mt. Etna, Italy. J. Appl.
Volcanol. 2017, 6, 12. https://doi.org/10.1186/s13617-017-0063-8.
12. Pavolonis, M.J.; Sieglaff, J.; Cintineo, J. Automated detection of explosive volcanic eruptions using satellite-derived cloud vertical growth rates. Earth Space Sci. 2018, 5, 903–928. https://doi.org/10.1029/ 2018EA000410
13. Paredes-Mariño, J.; Forte, P.; Alois, S.; Chan, K.L.; Cigala, V.; Mueller, S.B.; Poret, M.; Spanu, A.; Tomašek, I.; Tournigan, P.-Y.;
et al. The lifecycle of volcanic ash: Advances and ongoing challenges. Bull. Volcanol. 2022, 84, 51. https://doi.org/10.1007/s00445-
022-01557-5
14. Andronico, D.; Branca, S.; Calvari, S.; Burton, M.R.; Caltabiano, T.; Corsaro, R.A.; Del Carlo, P.; Garfì, G.; Lodato, L.; Miraglia,
L.; et al. A multi-disciplinary study of the 2002–03 Etna eruption: Insights for a complex plumbing system. Bull. Volc. 2005, 67,
314–330. https://doi.org/10.1007/s00445-004-0372-8.
15. Branca, S.; Del Carlo, P. Types of eruptions of Etna volcano AD 1670-2003: Implications for short-term eruptive behaviour. Bull.
Volcanol. 2005, 67, 732–742.
16. Spampinato, L.; Calvari, S.; Oppenheimer, C.; Lodato, L. Shallow magma transport for the 2002–2003 Mt. Etna eruption inferred
from thermal infrared surveys. J. Volcanol. Geotherm. Res. 2008, 177, 301–312. https://doi.org/10.1016/j.jvolgeores.2008.05.013.
17. Bonaccorso, A.; Bonforte, A.; Calvari, S.; Del Negro, C.; Di Grazia, G.; Ganci, G.; Neri, M.; Vicari, A.; Boschi, E. The initial phases
of the 2008–2009 Mt. Etna eruption: A multi-disciplinary approach for hazard assessment. J. Geophys. Res. 2011, 116, B03203.
https://doi.org/10.1029/2010JB007906.
18. Bonaccorso, A.; Calvari, S. Major effusive eruptions and recent lava fountains: Balance between erupted and expected magma
volumes at Etna volcano. Geophys. Res. Lett. 2013, 40, 6069–6073. https://doi.org/10.1002/2013GL058291.
19. Wadge, G.; Walker, G.P.L.; Guest, J.E. The output of the Etna volcano. Nature 1975, 255, 385–387.
https://doi.org/10.1038/255385a0.
20. Wadge, G.; Guest, J.E. Steady-state magma discharge at Etna 1971–1981. Nature 1981, 294, 548–550.
https://doi.org/10.1038/294548a0.
21. Harris, A.J.L.; Steffke, A.; Calvari, S.; Spampinato, L. Thirty years of satellite-derived lava discharge rates at Etna: Implications
for steady volumetric output. J. Geophys. Res. 2011, 116, B08204; Erratum in J. Geophys. Res. 2012, 117, B08207.
22. Alparone, S.; Andronico, D.; Lodato, L.; Sgroi, T. Relationship between tremor and volcanic activity during the Southeast Crater
eruption on Mount Etna in early 2000. J. Geophys. Res. 2003, 108, 2241. https://doi.org/10.1029/2002JB001866.
23. Cannata, A.; Montalto, P.; Privitera, E.; Russo, G.; Gresta, S. Tracking eruptive phenomena by infrasound: 13 May 2008 eruption
at Mt. Etna. Geophys. Res. Lett. 2009, 36, 5.
24. Spampinato, L.; Sciotto, M.; Cannata, A.; Cannavò, F.; La Spina, A.; Palano, M.; Salerno, G.G.; Privitera, E.; Caltabiano, T. Multiparametric study of the February–April 2013 paroxysmal phase of Mt. Etna New South-East crater. Geochem. Geophys. Geosyst.
2015, 16, 1932–1949. https://doi.org/10.1002/ 2015GC005795.
25. D’Agostino, M.; Di Grazia, G.; Ferrari, F.; Langer, H.; Messina, A.; Reitano, D.; Spampinato, S. Volcano Monitoring and Early
Warning on Mt Etna Based on Volcanic Tremor—Methods and Technical Aspects; Nova Science Publishers: New York, NY, USA,
2013; Volume 4, pp. 53–92.
26. Patanè, D.; Di Grazia, G.; Cannata, A.; Montalto, P.; Boschi, E. Shallow magma pathway geometry at Mt. Etna volcano. Geochem.
Geophys. Geosyst. 2008, 9, Q12021. https://doi.org/10.1029/2008GC002131.
27. Cannavò, F.; Sciotto, M.; Cannata, A.; Di Grazia, G. An integrated geophysical approach to track magma intrusion: The 2018
Christmas eve eruption at Mt. Etna. Geophys. Res. Lett. 2019, 46, 8009–8017. https://doi.org/10.1029/2019GL083120.
28. Sciotto, M.; Cannata, A.; Prestifilippo, M.; Scollo, S.; Fee, D.; Privitera, E. Unravelling the links between seismo-acoustic signals
and eruptive parameters: Etna lava fountain case study. Sci. Rep. 2019, 9, 16417. https://doi.org/10.1038/s41598-019-52576-w
29. Bonaccorso, A.; Currenti, G.; Linde, A.T.; Sacks, S. New data from borehole strainmeters to infer lava fountain sources (Etna
2011–2012). Geophys. Res. Lett. 2013, 40, 3579–3584.
30. Bonaccorso, A.; Linde, A.T.; Currenti, G.; Sacks, S.; Sicali, A. The borehole dilatometer network of Mount Etna: A powerful tool
to detect and infer volcano dynamics. J. Geophys. Res. 2016, 121, 4655–4669.
31. Bonaccorso, A.; Carleo, L.; Currenti, G.; Sicali, A. Magma Migration at Shallower Levels and Lava Fountains Sequence as Revealed by Borehole Dilatometers on Etna Volcano. Front. Earth Sci. 2021, 9, 740505.
32. De Gori, P.; Giampiccolo, E.; Cocina, O.; Branca, S.; Doglioni, C.; Chiarabba, C. How Long Re-pressurized Magma Can Feed
Eruptions at Mt. Etna. Commun. Earth Environ. 2021, 2, 216. https://doi.org/10.1038/s43247-021-00282-9.
33. Scollo, S.; Prestifilippo, M.; Spata, G.; D’Agostino, M.; Coltelli, M. Monitoring and forecasting Etna volcanic plumes. Nat. Hazards
Earth Syst. Sci. 2009, 9, 1573–1585.
34. Scollo, S.; Prestifilippo, M.; Bonadonna, C.; Cioni, R.; Corradini, S.; Degruyter, W.; Rossi, E.; Silvestri, M.; Biale, E.; Carparelli,
G.; et al. Near-real-time tephra fallout assessment at Mt. Etna, Italy. Remote Sens. 2019, 11, 2987.
35. Ganci, G.; James, M.R.; Calvari, S.; Del Negro, C. Separating the thermal fingerprints of lava flows and simultaneous lava fountaining using ground-based thermal camera and SEVIRI measurements. Geophys. Res. Lett. 2013, 40, 5058–5063.
36. Ganci, G.; Harris, A.J.L.; Del Negro, C.; Guéhenneux, Y.; Cappello, A.; Labazuy, P.; Calvari, S.; Gouhier, M. A year of lava
fountaining at Etna: Volumes from SEVIRI. Geophys. Res. Lett. 2012, 39, L06305.
37. Walker, G.P.L. Explosive volcanic eruptions—A new classification scheme. Geol. Rundsch. 1973, 62, 431–446.
38. Harris, A.J.L.; Dehn, J.; Calvari, S. Lava effusion rate definition and measurement: A review. Bull. Volcanol. 2007, 70, 1–22.
https://doi.org/10.1007/s00445-007-0120-y.
39. Bonaccorso, A.; Calvari, S. A new approach to investigate an eruptive paroxysmal sequence using camera and strainmeter
networks: Lessons from the 3–5 December 2015 activity at Etna volcano. Earth Plan. Sci. Lett. 2017, 475, 231–241.
https://doi.org/10.1016/j.epsl.2017.07.020.
40. Scollo, S.; Prestifilippo, M.; Pecora, E.; Corradini, S.; Merucci, L.; Spata, G.; Coltelli, M. Eruption column height estimation of
the 2011–2013 Etna lava fountains. Ann. Geophys. 2014, 57, S0214.61.
41. Corradini, S.; Montopoli, M.; Guerrieri, L.; Ricci, M.; Scollo, S.; Merucci, L.; Marzano, F.; Pugnaghi, S.; Prestifilippo, M.; Ventress,
L.; et al. A Multi-Sensor Approach for Volcanic Ash Cloud Retrieval and Eruption Characterization: The 23 November 2013
Etna Lava Fountain. Remote Sens. 2016, 8, 58.
42. Corradini, S.; Guerrieri, L.; Lombardo, V.; Merucci, L.; Musacchio, M.; Prestifilippo, M.; Scollo, S.; Silvestri, M.; Spata, G.; Stelitano, D. Proximal Monitoring of the 2011–2015 Etna Lava Fountains Using MSG-SEVIRI Data. Geosciences 2018, 8, 140.
43. Ganci, G.; Vicari, A.; Fortuna, L.; Del Negro, C. The HOTSAT volcano monitoring system based on a combined use of SEVIRI
and MODIS multispectral data. Ann. Geophys. 2011, 54, 5. https://doi.org/10.4401/ag-5338. 2011
44. Ganci, G.; Bilotta, G.; Cappello, A.; Hérault, A.; Del Negro, C. HOTSAT: A multi-platform system for the satellite thermal monitoring of volcanic activity. Geol. Soc. Lond. Spec. Publ. 2016, 426, 207–221. https://doi.org/10.1144/SP426.21.
45. Di Grazia, G.; Falsaperla, S.; Langer, H. Volcanic tremor location during the 2004 Mount Etna lava effusion. Geophys. Res. Lett.
2006, 33, 4.
46. Cannata, A.; Di Grazia, G.; Aliotta, M.; Cassisi, C.; Montalto, P.; Patanè, D. Monitoring seismo-volcanic and infrasonic signals
at volcanoes: Mt. Etna case study. Pure and Applied Geophysics 2013, 170, 1751–1771.
47. Cannata, A.; Montalto, P.; Privitera, E.; Russo, G. Characterization and location of infrasonic sources in active volcanoes: Mount
Etna, September–November 2007. J. Geophys. Res. 2009, 114, B8.
48. Johnson, J.B.; Aster, R.C.; Ruiz, M.C.; Malone, S.D.; McChesney, P.J.; Lees, J.M.; Kyle, P.R. Interpretation and utility of infrasonic
records from erupting volcanoes. J. Volcanol. Geoth. Res. 2003, 121, 15–63.
49. Cannata, A.; Sciotto, M.; Spampinato, L.; Spina, L. Insights into explosive activity at closely-spaced eruptive vents using infrasound signals: Example of Mt. Etna 2008 eruption. J. Volcanol. Geoth. Res. 2011, 208, 1–11.
50. Currenti, G.; Zuccarello, L.; Bonaccorso, A.; Sicali, A. Borehole Volumetric Strainmeter Calibration From a Nearby Seismic
Broadband Array at Etna Volcano. J. Geophys. Res. 2017, 112, 7729–7738.
51. Currenti, G.; Bonaccorso, A. Cyclic magma recharge pulses detected by high-precision strainmeter data: The case of 2017 intereruptive activity at Etna volcano. Sci. Rep. 2019, 9, 1–7.
52. Tamura, Y.; Sato, T.; Ooe, M.; Ishiguro, M. A procedure for tidal analysis with a Bayesian information criterion. Geophys. J. Int.
1991, 104, 507–516.
53. Ichihara, M. Seismic and infrasonic eruption tremors and their relation to magma discharge rate: A case study for sub-Plinian
events in the 2011 eruption of Shinmoe-dake, Japan. J. Geophys. Res. 2016, 121, 7101–7118.
54. Barth, A.; Newcombe, M.; Plank, T.; Gonnermann, H.; Hajimirza, S.; Soto, G.J.; Saballos, A.; Hauri, E. Magma decompression
rate correlates with explosivity at basaltic volcanoes—Constraints from water diffusion in olivine. J. Volcanol. Geoth. Res. 2019,
387, 106664.
55. Mastin, L.G.; Guffanti, M.; Servranckx, R.; Webley, P.; Barsotti, S.; Dean, K.; Durant, A.; Ewert, J.W.; Neri, A.; Rose, W.I.; et al.
A multidisciplinary effort to assign realistic source parameters to models of volcanic ash-cloud transport and dispersion during
eruptions (Book review). J. Volcanol. Geotherm. Res. 2009, 186, 10–21.
56. Andronico, D.; Scollo, S.; Cristaldi, A. Unexpected hazards from tephra fallouts at Mt Etna: The 23 November 2013 lava fountain.
J. Volcanol. Geotherm. Res. 2015, 304, 118–125.
57. Patanè, D.; Aiuppa, A.; Aloisi, M.; Behncke, B.; Cannata, A.; Coltelli, M.; Salerno, G. Insights into magma and fluid transfer at
Mount Etna by a multiparametric approach: A model of the events leading to the 2011 eruptive cycle. J. Geophys. Res. 2013, 118,
3519–3539.