Volcanoes under the Mediterranean surface may surprise many, and Europe’s largest is Marsili. Located off the northern Sicilian coast in the Tyrrhenian Sea, it remains quiet for long spans yet is not fully inactive. Its very existence hints at a dynamic underwater landscape that holds many of the region’s unanswered questions.
Marsili was first identified around 1920 by Italian scientist Luigi Ferdinando Marsili, which explains its name. Beginning in 2005, researchers used advanced techniques to study the cone in greater detail. Even with these efforts, numerous aspects of Marsili still resist complete explanation, inviting ongoing scientific curiosity.
The sheer scale is striking: the volcanic cone rises approximately 3,000 meters from the seafloor, with its summit about 450 meters below the surface. The base stretches roughly 70 kilometers, and the total area covers about 2,100 square kilometers, a size comparable to the island of Tenerife. Marsili is not alone. It sits among a cluster of volcanoes off the northern edge of Sicily and along Italy’s west coast. Many volcanic formations began shaping the present-day land, such as the Aeolian Islands—Stromboli, Lipari, Salina, Filicudi, Alicudi, Panarea, and Vulcano. For every visible island, there are ten more volcanoes hidden beneath the sea.
Experts classify Marsili as potentially dangerous because it could trigger a tsunami reaching about 20 meters in height, with impacts along the Tyrrhenian shoreline. In fact, Marsili is regarded as an active volcano, accompanied by several smaller satellite cones in the vicinity.
Possible landslide generating a tsunami
Research indicates the last eruption occurred several thousand years ago. Today, activity is still detectable in the form of gas emissions, minor tremors, and faint roars, but at low energy. Like Magnaghi, Vavilov, and Palinuro, Marsili is considered one of the most hazardous cones in this region of the Mediterranean. The volcano shows clear signs of instability, particularly near its summit, where the rock is low density and weakened by hydrothermal activity. This instability leaves room for the possibility of massive submarine landslides that could unleash a tsunami.
Radar imagery highlights the surrounding area as a zone of interest, underscoring the vulnerability of nearby underwater structures and the potential for sudden shifts.
These strong waves could affect coastal communities in Campania, Calabria, and Sicily, especially during peak tourist season. Seismologist Enzo Boschi, a former head of Italy’s National Institute of Geophysics and Volcanology, notes that Marsili is active and could erupt at any time. Yet the most dangerous scenario is not a surface eruption but a collapse of submerged rocks, which would displace large volumes of water and generate extreme waves. The level of explosiveness remains debated among scientists, and the deep location complicates research efforts.
Boiling water as a surface sign
The main surface indicator in the event of an explosion would be boiling water. Gas emissions from the cone, similar to what was observed on El Hierro in the Canary Islands in 2011, would accompany this sign. According to the Italian volcanic institute, visible surface markings would likely consist of boiling water, degassing, and buoyant volcanic material such as pumice remaining suspended for weeks. While the possibility of eruption cannot be ruled out, INGV offers a cautious assessment: the risk of surface eruptions affecting sea routes is extremely low, and a strong explosion would be noticed mainly as a temporary disruption of sea traffic. Still, a portion of the volcanic cone collapsing could produce a tsunami due to the large displaced water volume. Deformations from magma uplift could drive instability in parts of the cone, a scenario that cannot be completely excluded in advance. Given the limited data, researchers continue monitoring Marsili to build a clearer picture of its behavior.
While this article cannot provide a definitive forecast, ongoing studies aim to improve risk understanding and early warning capabilities for the Mediterranean seabed area. More data and analysis are needed to refine models and ensure robust preparedness for coastal populations and maritime activities.