A volcanic eruption that occurred during a snowstorm at the end of May had generated a pyroclastic flow that remained “unnoticed” for about 10 days, until weather conditions improved and researchers were able to access the summit areas of the volcano. It might seem like literature but this is what happened last May 21, 2023 on Etna, as described in the study “A Hidden Eruption: The 21 May 2023 Paroxysm of the Etna Volcano (Italy)” created by a team of researchers from the National Institute of Geophysics and Volcanology (INGV), the Sapienza University of Rome, the University of L'Aquila and the University of Cagliari.
“Our work, in addition to scientifically describing the eruptive event that affected the South-East crater of Etna, wanted to draw attention to the importance and effectiveness of the INGV remote monitoring systems”, explains Emanuela De Beni, volcanologist at the Etna Observatory and co-author of the study.
The bad weather had obscured the video surveillance cameras installed on the volcano
“In fact – continues De Beni – despite the bad weather having obscured the video surveillance cameras installed on the volcano, the other volcanological monitoring stations worked correctly and the signals promptly reached our Operations Room in Catania, signaling to us that an eruption was underway with lava fountain and emission of two flows, one towards the South and the other towards the East”.
A week after the eruption, INGV researchers went to the summit area to carry out surveys with drones and proceed with the mapping and quantification of the erupted products. “Once we arrived on site we realized that a deposit which we had not been aware of until then had actually overlapped the southern flow”, continues De Beni: “After careful soil investigations and sedimentological analyses, we discovered that it was a 'pyroclastic density current' (PDC), that is, a flow of magmatic material mixed with gas at high temperatures that had descended at high speed from the flanks of the volcano.”
At that point, the field and drone surveys were accompanied by the analysis of satellite images and radar data provided by the airports of Catania-Fontanarossa and Reggio Calabria-Tito Minniti and by a plant on Monte Lauro (SR), as well as the study in-depth analysis of the volcanic tremor and infrasound provided by the INGV monitoring systems. All this has made it possible to reconstruct the emission of an ash column (so-called plume) with a height of between 10 and 15 kilometres, the result of an eruption divided into three phases: a first weakly Strombolian phase, a true Strombolian phase and finally, a lava fountain.
Etna is a constantly changing volcano
Etna, a continuously changing volcano, has once again made it clear how it can generate various and potentially dangerous volcanological phenomena, which must be constantly monitored. “Three drone campaigns were necessary, during which 2,311 thermal and non-thermal images were captured, then processed to create the map and quantification of the erupted products, and another field campaign aimed at sampling the current deposit pyroclastic”, adds De Beni.
“This teamwork has once again highlighted the fundamental importance of the INGV-OE remote volcanological monitoring system, but also of the still essential direct observation of the field geologist which allowed us to recognize the pyroclastic flow, otherwise not identifiable remotely”, concludes the researcher.
Here is the complete study