Amazing as it sounds, there are volcanoes buried beneath the Mediterranean, and among them is a true giant: Marsili, Europe’s largest submarine volcano, located to the north of Sicily in the Tyrrhenian Sea. Quiet for thousands of years, its presence remains far from inactive.
The volcano traces its name to the Italian explorer Luigi Ferdinando Marsili, who identified it in the 18th century but it has only yielded to modern study since 2005 thanks to advanced oceanographic techniques. Even today many of its inner workings resist full scientific revelation.
The cone rises about 3,000 meters from the seafloor, with the summit lying roughly 450 meters below the surface. Its base spans about 70 kilometers, giving it a total area around 2,100 square kilometers, a size comparable to Tenerife itself. Marsili is just one member of a family of volcanic systems scattered off the northern Sicilian coast and the western coast of southern Italy. While the Aeolian islands like Stromboli, Lipari, Salina, Filicudi, Alicudi, Panarea and Vulcano are visible above water, there are many more volcanoes hidden beneath the sea that outnumber them in abundance by a wide margin.
Experts categorize Marsili as potentially dangerous because it could generate a tsunami reaching up to twenty meters in height, capable of impacting shores around the Tyrrhenian Sea. In fact, Marsili remains active and is accompanied by numerous small volcanic satellites in its vicinity.
Possible landslide generating a tsunami
Research indicates that the last eruption occurred several thousand years ago. Today the volcano still exhibits activity, but in limited form, marked by minor rumblings, gas emissions and low-energy tremors.
Marsili, Magnaghi, Vavilov and Palinuro are regarded as among the most hazardous mafic structures in this part of the Mediterranean. The risk of collapse is comparable to nearby Vavilov, with serious implications for coastal regions. Current data show significant instability, especially near the summit where weak, low-density rocks have been altered by surrounding hydrothermal processes. The possibility of massive landslides remains on the table and could drive a hypothetical tsunami when combined with displacement of submerged rock.
This instability could affect densely populated sectors in Campania, Calabria and Sicily, particularly during peak tourist seasons. Seismologists stress that the event could involve an explosive release, though this is a matter of debate among experts, and it remains difficult to study at the depths where Marsili sits.
Boiling water as a surface sign
In the event of a major explosion, the surface may reveal only boiling water caused by degassing and the buoyancy of volcanic materials, such as pumice, which could stay afloat for weeks. The Italian volcanic institute notes that surface signs would be limited, while gas emissions from the cone would be monitored from below the water surface.
While the possibility of an eruption cannot be ruled out entirely, official assessments emphasize calm about surface risk: the chance of a sea eruption is considered very low, and an explosion surpassing five hundred meters in scale would likely result in only temporary diversions of transport routes. Yet, a consequential displacement of submerged rock could still trigger a tsunami, depending on how the structure deforms and magma movements unfold. Scientists caution that ongoing deformation and magma inflation could change the risk profile, and more studies are essential to form clearer predictions.
Given the lack of conclusive data about Marsili, researchers—along with national institutions like the Italian National Institute of Geophysics and Volcanology (INGV)—continue to monitor the system. The goal is to improve understanding of its behavior and potential impacts on nearby populations, while balancing scientific curiosity with public safety.
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