The southwestern coast of Sicily is, by every available measure of European coastal demography, one of the more densely populated coastlines on the continent. The coastline has been inhabited continuously for several thousand years. The waters off the coastline have been navigated by various commercial, military, and recreational vessels for nearly as long. The seafloor off the coastline has been, in some real way, one of the more thoroughly surveyed underwater regions of the Mediterranean, by virtue of the structural 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 wider register has not, on the available evidence, adequately registered is that the thoroughness of the surveying has been considerably less complete than the cultural framing of the region has been treating it as. A research expedition, conducted across three weeks in 2025 and the findings of which have been recently published, has identified six previously unknown volcanic structures in the Sicilian Channel, the body of water between Sicily and Tunisia. One of these structures, named Actea, sits approximately six kilometers from the southwestern coast of Sicily. The structure is, by every available measure of underwater geology, a substantial feature of the seafloor. The structure was not, until very recently, on any of the existing maps of the region.
What the expedition actually found
It is worth being precise about what the expedition actually found, because the wider register has tended to absorb the discovery in vaguer terms than the underlying findings warrant.
The expedition was called M191 SUAVE, which stands for Submarine Volcanism in the Western Sicilian Channel. The expedition was conducted aboard the German research vessel METEOR. According to the GEOMAR documentation of the mission, the expedition brought together an international team of scientists from the GEOMAR Helmholtz Centre for Ocean Research in Kiel, the Monterey Bay Aquarium Research Institute, Italy’s National Institute of Oceanography and Experimental Geophysics, Victoria University of Wellington, and the Universities of Malta, Birmingham, and Oxford. The team spent three weeks scanning the seafloor of the Sicilian Channel using a multibeam echosounder and a magnetometer, designed to map volcanic structures both exposed on the surface and buried in sediment.
The investigations revealed three volcanic centers that were at least six kilometers wide and 150 meters high. The dimensions are, on close examination, structurally substantial. A volcanic center 150 meters high is approximately the height of the Tour Montparnasse in Paris. The wider register has tended to assume that features of this scale, located in a busy and well-trafficked stretch of the Mediterranean, would have been identified long before the present. The wider register has been wrong about this.
The most striking of the individual structures is the one named Actea. According to the Daily Galaxy coverage, Actea sits approximately six kilometers off the southwestern coast of Sicily. The structure is a volcano, wrapped in a solidified lava flow that extends approximately four kilometers to the west. The structure was, until the expedition’s sonar data revealed it, not on any of the existing maps of the region.
What the lead researchers actually said
The reaction of the researchers themselves, on close examination, is worth attending to, because the reaction reveals something about how thoroughly the region had been assumed to be surveyed.
Emanuele Lodolo, a researcher at Italy’s National Institute of Oceanography and Experimental Geophysics, was on board the METEOR when the sonar data first revealed Actea. His published reaction to the discovery is straightforward and worth quoting directly. “We were quite surprised about this,” he said, “because we were really very close to the coast.” The surprise is, on close examination, the structurally interesting feature of the moment. The researchers were not, by any standard methodological framing, expecting to discover anything of this scale in a region that had been so close to one of the more populated coastlines in Europe for so long.
Dr. Jörg Geldmacher, the chief scientist of the expedition and a marine geologist at GEOMAR, has been similarly direct about the scientific significance. His published comments on the expedition’s findings note that while the surprise discoveries were interesting, the structurally more important achievement from a scientific standpoint was the retrieval of excellent igneous rock samples from the volcanic centers. The samples will, on the available scientific protocols, allow the team to conduct detailed geochemical analyses that will reveal the structural history of the volcanic activity in the region. The samples are the substantive scientific product. The surprise of the discoveries themselves is what the wider register has been responding to.
What this implies about how much we actually know about the seafloor
The structural implication of the finding, on close examination, is considerably more substantial than the wider register has been treating it as. The implication is that the wider scientific community’s confidence about how thoroughly the various coastlines of the world’s most populated regions have been surveyed is, in some real way, considerably less warranted than the standard cultural framing of the question would suggest.
The Sicilian Channel is, by every available measure of how thoroughly the Mediterranean has been studied, one of the more well-surveyed underwater regions on the planet. The region has been the subject of continuous scientific attention for several decades. The region is heavily trafficked by commercial shipping. The region is 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 2025, the implications for what else might be undetected in the various less thoroughly surveyed underwater regions of the world are, on close examination, considerable.
The wider scientific community has been increasingly explicit about this implication. According to the Mongabay coverage of the wider Italian coastal mapping project that is currently underway, Italy is the 14th-longest coastline of any country in the world, and the project to comprehensively map the entire Italian coast was only begun in July 2024 and is scheduled to be completed by June 2026. The very fact that such a project is being conducted only now, in 2025 and 2026, reveals that the previous mapping of the region was considerably less comprehensive than the cultural framing of the region’s underwater geography would have suggested.
What the shipwreck on the Nameless Bank actually was
The structural feature of the expedition that has received less popular attention than the volcanic discoveries, but that is on close examination similarly informative about the thoroughness of the previous surveying, is the discovery of a substantial shipwreck on the Nameless Bank.
The Nameless Bank is located approximately halfway between the Italian island of Linosa and the Sicilian coast. The bank is, by every available measure, well-known to the various commercial and scientific vessels operating in the region. The seafloor surrounding the bank has been the subject of repeated surveying across the decades. The shipwreck the SUAVE expedition discovered there, in 110 meters of water, is 100 meters long and 17 meters wide. The dimensions are, on close examination, substantial. The wreck is, by every available measure of the standard shipwreck-detection methodologies, structurally large enough that previous surveys should have been expected to identify it.
The previous surveys did not identify it. The SUAVE expedition’s high-resolution mapping did. The wreck’s position has been reported to the Italian authorities. The implication is, on close examination, structurally similar to the implication of the volcanic discoveries. The previous surveying of the region, despite the considerable scientific attention the region has received over the decades, was considerably less complete than the wider cultural framing of the region has been treating it as.
What this implies for the wider seafloor
The wider seafloor of the planet’s oceans is, on the available estimates from the various organizations conducting seafloor mapping, considerably less comprehensively mapped than the wider cultural framing has tended to assume. Other recent expeditions in the same general region have produced similarly striking discoveries, including a 1,500-meter-tall ancient waterfall buried beneath the seafloor south of Sicily, identified by a different METEOR expedition in 2024.
The various recent discoveries are, on close examination, structurally consistent with each other. The discoveries suggest that the Mediterranean, which the wider cultural framing has tended to treat as one of the most thoroughly studied bodies of water on the planet, has been considerably less thoroughly studied than the framing suggests. The implications for the rest of the world’s oceans, which have received considerably less scientific attention than the Mediterranean, are correspondingly larger.
What is being demonstrated, by the cumulative evidence of these discoveries, is that the planet’s underwater geography remains, in some real way, considerably less well-known than the cultural framing of the question has been treating it as. The remaining unknowns are not located only in the deep ocean or in the structurally remote regions of the planet. The remaining unknowns are located, in many cases, within kilometers of some of the most densely populated coastlines on the planet.
The acknowledgment this article wants to leave
The M191 SUAVE expedition has identified, on the available evidence published in May 2025 and the months following, six previously unknown volcanic structures in the Sicilian Channel. The most striking of these, named Actea, sits approximately six kilometers off the southwestern coast of Sicily, wrapped in a solidified lava flow extending four kilometers to the west. The expedition has also identified three volcanic centers at least six kilometers wide and 150 meters high, and a previously undetected 100-meter shipwreck on the Nameless Bank between Linosa and Sicily.
The structural implication of these findings is that the seafloor of one of the most well-surveyed underwater regions in the world contained, until very recently, substantial features that the existing maps did not show. The features have been sitting where they are for considerably longer than the period in which surveying technology has been available to detect them. The features were not, in any meaningful sense, hidden. The features were, more accurately, simply not yet looked at by anyone with the equipment and the motivation to actually find them. The wider register would benefit, on the available evidence, from absorbing what this implies about how much remains unmapped in the various other regions of the planet’s oceans that have received considerably less scientific attention than the Sicilian Channel. The absorbing, modestly, is what the next several decades of seafloor mapping is going to be required to do.
