2024-02-23 11:09:02
AGI – After thirteen days of navigation off the coast of Catania, the Meteor M198 expedition organized by the Geomar oceanographic research center in Kiel (Germany) ended. The National Institute of Geophysics and Volcanology also participated in the scientific cruise, whose main purpose was to investigate the submerged portions of the south-eastern flank of Etna in constant movement under the waters of the Mediterranean.
“The INGV has been monitoring the slow but progressive movements of Etna for several years”, explains Alessandro Bonforte, an INGV researcher who was on board the M198 expedition. “These small movements, which do not only involve the emerged part of the volcano, are not normally particularly dangerous, however – he adds – in some cases and in particular conditions they can become more substantial and give rise, in addition to the well-known earthquakes which periodically affect the eastern flank, also, for example, to submarine landslides”.
The expedition involved an international research team trying to understand whether the volcano’s southeastern flank stands sliding towards the Ionian as a single block or in several portions and what the origins of this dynamic are. “The most ambitious objective of our expedition was to highlight how underwater observations and measurements are fundamental to better understand structures such as Etna and complex phenomena such as the sliding of the side of a volcano into the sea, be it coastal such as Etna or insular. In this context, combining the datasets coming from the sea with those processed on land through structural, GNSS and satellite surveys allows us to have a real 360-degree observatory on the volcano”, continues Bonforte.
To obtain the necessary data, researchers on board the Meteor vessel took a multidisciplinary approach. In addition to the collection of rock and sediment samples and the mapping of the seabed carried out thanks to multibeam sonar and sophisticated underwater drones, geodetic techniques have made it possible to exploit a network of acoustic sensors already installed on the seabed off the coast of Catania in 2016 to calculate, based on the propagation times of sound waves, the relative sliding movements between the various points of the network.
These measurements have already made it possible to detect the active deformation on the continuation of the well-known Acitrezza fault, at least up to 1200 meters deep. Furthermore, the mission was an opportunity to experiment with a technique never before applied to volcanoes which involved the installation of two piezometers to measure the variations in pressure and temperature of the water contained in the first 5 meters of sediment on the seabed near the fault.
The objective, in this case, is to try to understand whether, as already highlighted in the case of some earthquakes, a movement of the volcano’s flank is accompanied or can be anticipated by changes in the characteristics of the fluids present inside it. “The paradigm we are adopting is to ‘remove the water’, at least as a mental limit. The coastline that delimits all the maps is in fact not a geological or geodynamic limit, but only a limit to our observation capabilities. Etna is among the best studied volcanoes in the world, an open-air laboratory, and this has allowed an enormous advancement in knowledge of the geological phenomena that characterize it; this makes the gap in knowledge on the side of the mountain that continues below even more evident of sea level”, adds Alessandro Bonforte.
Each oceanographic campaign adds a piece to the enormous spectrum of observations that can and must be conducted on the seabed in front of the volcano and poses, he concludes, new questions which we will try to answer with subsequent campaigns: “it is the essence of our work of researchers and the progress of knowledge, a stimulating journey full of questions to be answered”.
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