After a few months of relative calm, in the last two weeks the typical signs of awakening of the volcano to the summit craters of Etna are again being observed. Towards mid-March 2019 there began to be heard explosions created by Strombolian explosions deep inside the conduit of the Bocca Nuova, the largest of the summit craters. From the end of March onwards, the images of the satellite thermal sensors revealed thermal anomalies (Figure 1), both in correspondence with the western crater depression of the Bocca Nuova (BN-1), and, intermittently and in any case less accentuated, to the eastern mouth of the New Southeast Crater.
Figure 1 – Images of the Sentinel-2 satellite, which highlight the thermal anomalies detected at the summit craters of Etna on 31 March and 30 April 2019. There is a clear increase in the thermal anomaly at the BN-1 (depression western crater of the Bocca Nuova crater), while the thermal anomaly at the eastern mouth of the New Southeast Crater (NSEC) is no longer seen in the image of April 30th.
During the last days of April 2019, blasts of incandescent bombs were observed, which exceeded the height of the crater rim to fall back into the mouth itself. Finally, on the morning of May 1, newly erupted waste was found outside the crater rim, as it had not been observed since the morning of December 27, 2018.
This most recent activity did not concern only the Bocca Nuova. The Voragine crater, in fact, first formed two small collapsing craters (January 12th and April 18th 2019 respectively) that started emitting incandescent gases (Figure 2). Since April 20, these two mouths have also generated sporadic, modest explosions with ash emission, which determined their progressive enlargement until the two mouths welded together forming a single larger depression.
Figure 2 – North-eastern part of the crater Voragine with the three collapsing mouths formed, respectively, on 7 August 2016 (1), 12 January 2019 (2) and 18 April 2019 (3). Bottom right, corresponding thermal image, showing higher temperatures at vent 3; while that of 7 August 2016, which for over a year has emitted gas at very high temperatures, now emits only vapors at low temperatures. The images were taken by Stefano Branca, INGV-OE, on 19 April 2019.
The Northeast Crater, which between January and February 2019 had plentifully erupted dense gaseous plumes very rich in ash, on 26 April also generated small Strombolian explosions, which shortly after (28 April) began to affect the eastern mouth too of the New Southeast Crater. From 2 May, the activity intensified slightly at the New Southeast Crater, which produced small ash puffs sometimes mixed with incandescent pyroclastic material. Some scenes of these events are shown in Figure 3.
Figure 3 – Explosive events at the summit craters of Etna in the period between late April and early May 2019, taken up by the surveillance cameras of the INGV-Osservatorio Etneo. The images of April 25 (top left) and May 5 (bottom right) were recorded by the Montagnola camera (EMOV), installed 3 km south of the summit craters. The other two images come from the high resolution camera located on Monte Cagliato (EMCH), 8.3 km to the east from the summit craters.
These phenomena mark the resumption of eruptive activity on the summit craters of Etna, after just over two months of relative calm, marked almost exclusively by gas emissions. This recalls, to a certain extent, what happened in the period from June to July 2018, when a gradual reactivation of the summit craters was noticed after about a year of quiescence. In any case, the summit eruptive activity now in progress is the most characteristic and most frequent of Etna, and therefore the current awakening of the volcano is completely normal.
Article written by Boris Behncke and Marco Neri, using data obtained from the monitoring networks of the INGV.
