Etna update, 18/05/2023

Accompanied by earthquakes and a strong increase of the tremor, explosive activity started today in Bocca Nuova. In the meantime, the tremor has decreased again somewhat.

During the last 14 days, dense clouds, rain and fresh snow hindered the observation of Etna's summit region very often. During the cloud-free hours, the usual gas emissions appeared, which continued to be most vigorous at Bocca Nuova and often intensified in pulses.
At Voragine and Northeast Crater, I continued to observe no significant gas emissions. At the Southeast Crater complex, some gas was persistently emitted from the area of the central crater, between old and new Southeast Crater. Gas and white steam were also persistently emitted from the upper northern flank and the upper northeastern flank of New Southeast Crater.
On the morning of 14 May, a small explosive ash emission occurred at New Southeast Crater around 08:36. The starting point was apparently again a vent on the upper northeastern flank of the cone, which had already caused a similar explosion on 06 May. I could not observe further ash emissions there.

After a series of light earthquakes that occurred this morning between 03:00 and 09:00 on the eastern flank of Etna in the area of Acireale - Santa Venerina - Linera and in the Valle del Bove, respectively, the tremor began to increase significantly from about 12:00. However, bad weather with many clouds prevented the observations at first. Later, the weather cleared up a bit and now it became obvious that a lot of gas and steam was rising from Bocca Nuova. From about 17:00, a small thermal anomaly was also visible over the central crater cone via the thermal imaging camera in Bronte, suggesting the release of hot material from Bocca Nuova. Other thermal anomalies were visible until at least 20:00, but appeared weaker than before despite better weather.

In the meantime, INGV has confirmed the explosive activity in Bocca Nuova. It is reported that the explosive activity started around 17:00. No ash has been emitted so far. The increase in tremor has continued, according to INGV. The source of the tremor was located between Bocca Nuova and Southeast Crater at about 2500 m altitude. The explosive activity could also be detected by infrasound from 17:00. As further reported, a seismic crisis started around 16:45 in the summit area of Etna. The strongest quake was recorded at 17:00 with a magnitude of 1.9. Also starting at 16:45, the clinometric stations in the summit area of Etna showed a change of two microradians. Slightly weakened, this change was also visible at lower stations [1].

In the last two weeks, small signals reminiscent of explosion signals were visible on the online seismograms of station ECNE about every 30 minutes. Due to strong tremor, the online signals were overlaid by strong noise from about 12:00 on May 18.
The tremor had increased slightly on May 12, remained at a medium level, decreased again slightly from May 16, and then began to increase significantly on May 18 at about 12:00. The tremor reached the preliminary peak around 17:00, then it decreased slightly again [2].

On 10.05. several earthquakes occurred in the Linera - San Giovanni Bosco area (eastern flank), the strongest having a magnitude of 2.4. On 13.05. an earthquake with a magnitude of 2.0 was recorded southeast of Paternò (southern flank). On 17.05. an earthquake of magnitude 1.8 occurred southwest of Monte Scorsone (eastern flank). On 18.05. several earthquakes occurred at very shallow depths in the Santa Maria Ammalati - Mangano - Santa Tecla area (southeastern flank), with the strongest shaking reaching a magnitude of 3.2. On the same day, two earthquakes occurred at Linera (eastern flank), with magnitudes of 2.2 and 2.3, respectively. Also on 18.05., an earthquake of magnitude 2.0 occurred at Monte Centenari (eastern flank), followed by two earthquakes of magnitudes 1.7 and 1.9, respectively, northeast of Monte Frumento Supino (New Southeast Crater area) [3].

My interpretation of the data and speculations about the further development:
The earthquakes on the southeast and east flanks of Etna that occurred early this morning were probably the response of a north-south trending fault to magma ascent. The magma ascent later became noticeable by significant changes in tilt of slopes at the clinometric stations. The final ascent was then also signaled by sharply increasing tremor. Apparently, the magma then found its way into Bocca Nuova, which has at least one open vent. There, strombolian explosions probably then occurred, as thermal anomalies were recorded over the summit crater. Apart from the explosive activity in Bocca Nuova, today's events remind me of November 15, 2022, when, accompanied by some earthquakes, the inclination of the mountain also changed rapidly and intense tremors started. At that time, however, there was no eruptive activity at first. However, it occurred 12 days later in the form of purely effusive activity at the Southeast Crater Complex. This activity continued until February of this year.
I think it is possible that the Southeast Crater Complex will be active again this time. There were already several light earthquakes there this afternoon. It could be that strombolian activity is starting at one of the vents, perhaps even the one that produced the two explosive ash emissions. However, it is also quite possible that an eruptive fissure, preferably on the southeast or northeast flank, opens and prolonged effusive activity resumes.
Of course, continued strombolian activity in Bocca Nuova is also conceivable, but I rather suspect that only the overpressure has discharged here and that Bocca Nuova will continue to serve for the release of the gases of the rising magma. The gas-depleted magma then slowly rises and seeks a weak spot, which as already mentioned should be found at the Southeast Crater Complex, and then generates purely effusive and longer-lasting activity. But maybe something completely different happens, because the old lady is always good for a surprise!

1 - INGV-Sezione di Catania. 2023. 2023-05-18 15:43:49 - INVIO COMUNICATO GENERICO DI ATTIVITà VULCANICA
2 - INGV-Sezione di Catania. 2023. Home. TREMORE VULCANICO. ECNE
3 - INGV. Osservatorio Etneo. Sorveglianza e Monitoraggio. DATABASE TERREMOTI. Localizzazioni di sala operativa. 2023.

Webcam photo by INGV - Bronte thermal cam (W flank):

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