The Meteor M198 expedition, spearheaded by the Geomar oceanographic research center in Kiel, Germany, recently concluded after thirteen days of sailing off the coast of Catania. The expedition’s primary objective was to probe into the submerged sections of the south-eastern flank of Etna, which are perpetually in motion beneath the Mediterranean waters. The National Institute of Geophysics and Volcanology was also part of this scientific voyage.
Alessandro Bonforte, an INGV researcher who joined the M198 expedition, sheds light on the phenomenon they have been monitoring for years: “Etna’s slow yet progressive movements are an ongoing area of study for us. These minor movements, involving not just the emerged part of the volcano but also the submerged, are typically not dangerous. However, in certain situations and under specific conditions, they can become more significant, leading to the well-known earthquakes that periodically affect the eastern flank, and potentially even causing submarine landslides.”
The expedition incorporated a globally represented research team that attempted to fathom whether the volcano’s southeastern flank is sliding towards the Ionian as a single, uniform block or in multiple parts. The team also worked to uncover the causes behind this dynamic. Bonforte further explains, “Our most ambitious goal was to emphasize the indispensability of underwater observations and measurements in comprehending structures like Etna and complex phenomena such as the sliding of a volcano’s side into the sea, whether coastal like Etna or insular. By merging the datasets obtained from the sea with those gathered on land using structural, GNSS, and satellite surveys, we can establish a comprehensive, 360-degree monitor of the volcano.”
To garner the required data, the researchers aboard the Meteor vessel adopted a multidisciplinary approach. This included collecting rock and sediment samples, mapping the seabed using multibeam sonar and sophisticated underwater drones, and harnessing geodetic techniques. These techniques enabled them to utilize a network of acoustic sensors, which were already installed on the seabed off the coast of Catania in 2016. The propagation times of sound waves were used to calculate the relative sliding movements between the different points of the network.
This methodology has helped detect active deformation along the well-known Acitrezza fault, extending at least 1200 meters deep. Additionally, the expedition provided an opportunity to test a technique never before used on volcanoes, namely the installation of two piezometers to measure pressure and temperature variations in the water within the first 5 meters of sediment on the seabed near the fault.
The aim here is to discern whether a movement of the volcano’s flank is accompanied or can be predicted by changes in the properties of the fluids inside it, a phenomenon previously observed in some earthquakes. Bonforte adds, “The paradigm we are adopting is to ‘remove the water,’ at least conceptually. The coastline, which defines all maps, is not a geological or geodynamic boundary but merely a limit to our observational capabilities. Etna is one of the best studied volcanoes globally, serving as an open-air laboratory. While this has led to significant advances in understanding its geological phenomena, it also underscores the lack of knowledge about the mountain’s side that extends below sea level.”
Bonforte concludes that each oceanographic campaign contributes to the vast range of observations that can and should be conducted on the seabed in front of the volcano. Additionally, it raises new questions that we will strive to answer in future campaigns: “this is the essence of our work as researchers and the advancement of knowledge, a stimulating journey filled with questions waiting to be answered.”
