The southwestern coast of Sicily is, by the standards of European coastal demography, one of the more densely populated coastlines on the continent. It has been inhabited continuously for several thousand years. The waters off it have been navigated by commercial, military, and recreational vessels for nearly as long. The seafloor in the area has been, on the standard cultural framing of the region, one of the more thoroughly surveyed underwater zones of the Mediterranean, by virtue of the fact that humans have been operating in the vicinity for the entirety of the period during which underwater surveying has been technologically possible.

What the standard framing has not adequately registered is that the thoroughness of the surveying has been considerably less complete than the cultural confidence in the region would suggest. A research expedition conducted in the summer of 2023, with its detailed findings published across the years that followed, identified six previously unknown volcanic edifices in the Sicilian Channel, the body of water between Sicily and Tunisia. One of them, named Actea, sits roughly six kilometers from the southwestern coast of Sicily. It is a substantial feature of the seafloor. It was not, until very recently, on any of the existing maps of the region.

What the expedition did

It is worth being precise about what the expedition did, because the popular coverage has tended to absorb the discovery in vaguer terms than the underlying work warrants.

The expedition was designated M191 SUAVE, an acronym for Submarine Volcanism in the Western Sicilian Channel. It ran from July 16 to August 5, 2023, aboard the German research vessel METEOR. The GEOMAR Helmholtz Centre’s announcement of the initial findings identifies the participating institutions: GEOMAR (which coordinated), the Monterey Bay Aquarium Research Institute in California, Italy’s National Institute of Oceanography and Experimental Geophysics (OGS), Victoria University of Wellington, and the Universities of Malta, Birmingham, and Oxford. Jörg Geldmacher of GEOMAR served as chief scientist; Aaron Micallef of MBARI was co-chief.

The team spent three weeks scanning the seafloor of the Sicilian Channel using a multibeam echosounder and a magnetometer, instruments designed to map volcanic structures both exposed on the surface and buried in sediment. The investigations revealed three large volcanic centers that were at least six kilometers wide and 150 meters above the surrounding seabed. A feature 150 meters high is roughly the height of the Tour Montparnasse in Paris, sitting entirely underwater and entirely absent from existing geological models.

The team also collected lava samples from the new volcanoes and from several previously known submarine volcanoes that had never been sampled before. Geldmacher’s published comments on the find make clear that, for him, the rock samples were the more important scientific product. “This surprising discovery is interesting,” he said of the volcanoes and the wreck, “but as a geochemist, I am more excited about the excellent igneous rock samples that we managed to retrieve from the volcanic centres.”

What the closer analysis revealed

The detailed analysis of the multibeam data took several more years to complete. The findings, including the formal naming of the individual volcanoes, were published in 2026. Daily Galaxy’s coverage of the published findings identifies the most striking of the new edifices as Actea, named by Emanuele Lodolo of OGS, one of the researchers who had been on board the METEOR when the sonar data first revealed it.

Lodolo’s published reaction is straightforward and worth quoting directly. “We were quite surprised about this,” he said, “because we were really very close to the coast.” Actea sits on the northern sector of the Capo Granitola fault zone, at depths between 62 and 70 meters, with a summit that rises to just 34 meters below sea level. That is shallower than many recreational diving sites along the same coastline.

Actea is wrapped in a solidified lava flow that extends roughly four kilometers to the west. It carries signs of magmatic reactivation, probably occurring sometime between the Last Glacial Maximum and the early post-glacial rise in sea level. A neighboring volcano, Climene, shares an intriguing trait with Actea: bubbles stream from both of their craters. Without chemical samples of the bubbles, the source cannot be definitively identified. The bubbles could signal biogenic methane venting. They could also indicate ongoing hydrothermal circulation. Either way, the seafloor here is not dead geology.

The shipwreck on the Nameless Bank

The feature of the expedition that has received less popular attention than the volcanic discoveries, but that is similarly informative about the thoroughness of the previous surveying, is the discovery of a substantial shipwreck on the Nameless Bank.

The Nameless Bank, Banco Senza Nome in Italian, sits roughly halfway between the Italian island of Linosa and the Sicilian coast. OGS’s announcement of the find describes the wreck as 100 meters long and 17 meters wide, lying in 110 meters of water. Those dimensions are substantial — the wreck is structurally large enough that previous surveys should have been expected to identify it.

They did not. The SUAVE expedition’s high-resolution mapping did. Its position was reported to the Italian maritime authorities. The implication is similar to the implication of the volcanic discoveries: the previous surveying of the region, despite the considerable scientific attention it has received over the decades, was less complete than the cultural framing of the region had been treating it as.

What this implies for the wider seafloor

The deeper implication of the finding is worth attending to. The Sicilian Channel is, by the standards of how thoroughly the Mediterranean has been studied, one of the more well-surveyed underwater zones on the planet. It has been the subject of continuous scientific attention for several decades. It is heavily trafficked by commercial shipping. It sits within sonar range of various Italian and Tunisian coastal facilities. If a volcano six kilometers wide and 150 meters high could remain undetected six kilometers off the southwestern coast of Sicily until 2023, the implications for what else might be undetected in the less thoroughly surveyed regions of the world’s oceans are considerable.

The wider scientific community has been increasingly explicit about this. As OGS itself noted in announcing the find, the new volcanoes join a series of smaller volcanic cones the institute had already discovered in 2019 in the marine area between Mazara del Vallo and Sciacca. The picture being built up across these investigations is one in which the seafloor of even the most heavily studied waters in Europe contains features that the existing maps did not show.

The same region has form for surprise. In July 1831, a submarine cone known as Ferdinandea beg