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Thanks to the very successful cooperation from previous years with scientists from the Instituto Nazionale di Geofisica e Vulcanologia, Osservatorio Etneo (INGV-OE) in Catania, Sicily, scientists from the Earth Science Institute SAS once again took part in the measurement campaign on Mount Etna at its summit parts. Etna's previous activity foreshadowed adventure and raised doubts as to whether measurements would even be possible.

At the beginning of July (4th and 7th), Etna spewed out two large, 1 km high lava fountains lasting several hours (so-called paroxysms), which dramatically changed the morphology of the summit craters. Recently, the Bocca Nuova and Voragine craters have merged into one, and today, there is talk of a central crater complex. These eruptions filled both craters and caused the cone of the central crater to rise by more than 100 m. The central crater outgrew the southeast (SE) crater (SEC) and became the current highest peak of Etna with a height of 3,369 metres above sea level.

The goal of the campaign was to supplement gravity data in the SE sector of the summit part of the volcano for the study of the construction of summit craters and their supply chimneys using gravimetric methods and 3D structural density modelling. In 2021, we measured gravity data in the northwest (NW) sector, while the SE sector was inaccessible to eruptions and the unstable terrain was covered by fresh volcanic products. In 2024, the opposite situation occurred, which actually helped us a lot. Returning to Etna to measure gravity data was made possible by the Transnational Access (TA) project with the acronym ETNAGRAV, financed by the EU through the multilateral GeoINQUIRE project. The project was awarded to the Earth Science Institute SAS, and the research team consisted of Peter Vajda (PI), Pavol Zahorec and Jaroslava Pánisová. A colleague from the Department of Theoretical Geodesy and Geoinformatics of the Slovak University of Technology in Bratislava, Juraj Papčo, also participated in the measurement campaign and was in charge of determining the exact location of the measured points using GNSS satellite methods (popularly known as GPS). We carried out the measurements with several colleagues from INGV-OE led by Filippo Greco.

Measurements during five days (July 11–15) were conducted in challenging terrain, in the relatively steep SE lower slopes of the summit craters, which were covered by the products of the 2022 and 2023 eruptions: ash, debris, and block lava flows. The terrain was unstable, the walk itself difficult. Feet dug deep into the ash that was sliding down the slope. Even worse were the broken cooled lava flows. The greatest attention had to be paid to the hidden cracks covered with ash. Going closer to the craters to the steeper slope was impossible from this side because of the risk of cracks and landslides.

The entire first day of measurements was accompanied by Stromboli activity in the central crater, which created a remarkable soundscape. The area of ​​Valle del Leone adjacent to the volcanological observatory of Pizzi Deneri (built in 1977 under the NE crater at an altitude of 2818 metres above sea level) was compared. On the second day, two half profiles were measured below the summit craters from the side of Pizzi Deneri.

On the third day, the plan was to measure the traverse from the south, from the area of ​​Torre del Filosofo (the former shelter and observatory at an altitude of approximately 2900 metres above sea level, buried by the eruptions in 2002 and 2003) to the NE, to the Pizzi Deneri observatory, and thus bridge the gap in gravity data in the SE sector. Halfway through the traverse, however, a warning came from the INGV monitoring centre in Catania of a possible eruption, which meant an immediate and rapid unavoidable escape from the traverse area vertically down the ledge directly into the Valle del Bove. The escape route led through very unstable, steep and rough lava terrain. The group had to descend1,600 meters, where we finally picked them up at the mouth of the valley with an all-terrain vehicle. This was the most demanding day of the entire campaign.

On the fourth day (July 14), we managed to do the traverse planned for the third day in parallel with the unfinished profile of the third day. As the survey team finished measurements on this traverse, approaching Pizza Deneri, located on the slope below the NE Crater (NEC), the crater emitted a relatively large cloud of volcanic ash. Although it looked ominous, the measuring party was not threatened. Satellite photos (Sentinel 2) showed that on July 17 there was already a lava lake in the NE crater. This crater also woke up during our presence.

On the fifth day, we conducted measurements on the SE side of the lower slopes of the summit craters from the Torre del Filosofo side. We finished the measurements in the afternoon and all that was left was a pleasant farewell dinner with Italian colleagues in a picturesque village on the south side of Etna. We didn't know yet what kind of surprise Etna herself was preparing for us at farewell.

During dinner in the restaurant garden, a rain of volcanic ash (fine debris) began to fall on our plates and glasses. Our hair (those of us who still have hair) was full of it. At the same time, news came that Etna spewed another 1 km high paroxysm (lava fountain mixed with volcanic clouds). Calmly but impatiently, we finished our dinner, bid farewell to our Italian colleagues, and moved on to our temporary home in Zafferana. From there, for long hours deep into the night, we gazed (and filmed) in awe at the show that "La signora", as the locals call Etna, prepared for us to say goodbye. The paroxysm lasted about seven hours. It once again covered the surrounding villages and towns with a layer of ash, so people woke up in the morning with brooms and mops in hand.

We are grateful that Etna granted us five days of measurements and waited with its paroxysm until the end of our campaign. Thanks to this, we successfully completed what we promised to deliver in the project. However, we are also grateful that we were able to experience Etna in its full beauty and power with our own eyes. It probably couldn't have been better timed. The next morning, we started our journey home, a little (or quite) overwhelmed, but full of impressions and a feeling of a job successfully completed.

Text a foto: Peter Vajda, Ústav vied o Zemi SAV, v. v. i., and team