Ovid, Enotrio and Diamante. Names that, once pronounced, bring to mind distant echoes of timeless myths and legends. Greek and Roman atmospheres, a taste of ancient glories that echo from Sulmona, the birthplace of the Roman poet of the "Metamorphoses", up to the noble villas whose remains we can still admire today from the coastal areas of lower Lazio to the southernmost tip of the boot.
For researchers who investigate the depths of the Mare NostrumHowever, this year the names Ovidio, Enotrio and Diamante have taken on a new, important meaning. In fact, those structures that until now were known only as underwater mountains, lying asleep on the bottom of the southern Tyrrhenian Sea, between the Aeolian arc and the Calabrian coasts, have actually turned out to be majestic extinct volcanoes formed in an as yet unspecified time between between 780.000 and 20.000 years ago.
A discovery of great scientific interest, which adds one more piece to the understanding of the geological nature of our territory and which opens up new scenarios in the study of the complex mosaic of ancient and recent volcanoes that populate the waters of the Tyrrhenian Sea. We talked about it with Riccardo De Ritis, INGV researcher and first author of the study that recently revealed the volcanic nature of these three imposing seamount.
Riccardo, the research of submarine volcanoes in the Mediterranean is a frontier of modern volcanology to which INGV has been dedicating itself for some time. Tell us something more…
Yes, indeed we have been dedicating ourselves to this work for several years: in 2008 we had already made a similar discovery in the Capo Vaticano area, near Tropea, an area not very far from the one covered by this latest publication, i.e. the marine sector in front Diamante and Scalea, in the province of Cosenza. What we are trying to do, in fact, is to analyze the seabed of the Tyrrhenian Sea close to the coast line to identify any submerged volcanic structures that have a significance in the context of the subduction system of the Calabrian arc, i.e. of that system in which the plate Ionic flows under the Calabrian arch and sinks into the mantle. We know the volcanism of the Aeolian Islands and how this fits into the context of Plate Tectonics, but we must remember that other possibilities of volcanism along the discontinuities that laterally limit the ion plate are also envisaged within the current vision of this theory. We then moved along the Palinuro chain, which a recent INGV publication from 2017 hypothesized to be the volcanic expression of one of these fractures. This chain has an extension of 90 km and our discovery shows that this is actually even more extensive in an easterly direction, reaching up to the coast of Calabria.
What did you find out exactly?
We discovered that Ovidio, Enotrio and Diamante, known to this day as simple seamount, or seamounts, are actually real volcanic structures. Although these volcanoes are part of the same geodynamic context of the Aeolian archipelago, they have different positions and geometries. We also realized that, overall, the mass of volcanic material emitted by the entire Palinuro chain is considerably more consistent than that emitted by the entire Aeolian archipelago (including its seamount): this is another important fact that gives even greater importance to the discovery.
What methods did you use to determine the volcanic nature of this submarine complex?
We became aware of the existence of these structures through an analysis of already existing data, in particular of the magnetic maps published by INGV between 2000 and 2004. Specifically, given that the area is typically characterized by an anomaly field magnetic anomaly, the fact of having identified a very extensive magnetic anomaly (about 14 km wavelength) immediately caught our eye, defining a first important indication of the presence of volcanic structures (volcanites are in fact very magnetic) , as well as the very first step of our research.
How did the investigation proceed?
At that point, aware of the result of 2008 at Capo Vaticano (there a magnetic anomaly was effectively followed by the discovery of a submarine volcano), we also looked at other geophysical data: a seismic section actually highlighted what I interpreted as an important ascent of volcanic material, only to then turn to the professionalism of Fabrizio Pepe of the University of Palermo for confirmation through other seismic sections interpreted by him; the high-resolution bathymetry carried out by a group of researchers from the CNR and Sapienza University coordinated by Francesco Chiocci, which highlighted the presence of structures with typically volcanic morphology in correspondence with the area where we had identified the first magnetic anomaly; and the seismic tomography carried out by my colleague Barbara Orecchio of the University of Messina, through which ab
We analyzed the speed of the seismic waves produced by earthquakes to reconstruct in three dimensions the properties of the materials of which the rocks crossed by the waves themselves are made. The tomography, in particular, allowed us to notice that in that area there seemed to be a degassing phase - present or past - of a cooling magmatic body. The natural next step was to join forces to interpret the data. We can therefore say that the definition of the volcanic nature of Enotrio, Ovidio and Diamante was possible thanks to the crossing of four different methods.
What do we know today about these volcanic structures?
We know that this volcanic complex, which has not shown signs of activity for at least 20.000 years, is made up of two different sectors: one near the coast, more superficial (the "peaks" of these seamounts are found at an average depth between 150 and 500 meters) and with a rounded morphology; the other further from the mainland, deeper and with steep, craggy ridges. The sector closest to the coast is the one in which Ovidio and Scalea fall (the latter unknown and "baptized" in our article). In particular, before having the high-resolution digital terrain model available, Ovid was thought to be unique seamount: We actually found it to be made up of five smaller, rounded, blunt, shallow depth seamounts. These are structures from a minimum of 200 to a maximum of 300 meters from the surrounding seabed, but with a very wide base: for example Scalea, which is one of these, is slightly larger than Vesuvius. This suggests that in the past these seamount were very large and that their vertical extension probably decreased over time due to both the erosion of currents and waves (once they lay near the surface of the sea), as well as the slow sliding down of the seabed, a phenomenon known as “subsidence”. Conversely, this fate did not happen to the other sector of the volcanic complex, ie the deepest one, which still has steep and "sharp" sections.
Along the coast of Calabria, between Diamante and Capo Vaticano, there is also a well-known thermal park, the Terme Luigiane. Is there a correlation between the discovered submarine volcanism and the hot springs themselves?
At the moment there is still no single answer to this question. Through the seismic profiles, in addition to the complex of volcanic buildings, during the research we have also identified the existence of intrusions, or processes whereby the magma that fails to reach the surface to feed the volcanic activity takes different directions, radiating along discontinuities and lines of weakness (for example faults) and cooling down inside the crust. They are therefore heat reservoirs which, as they cool, transfer heat to the hydrogeological system: this occurs along the entire Tyrrhenian coast, from the extinct volcanoes of Tuscany to Campania and the Aeolian Islands. Our seismic sections have identified about 5 km from the Calabrian coast, very close to the Terme Luigiane, heat-bearing structures deriving from this volcanic activity. So what is hypothesized is that the heat that feeds these baths derives from this volcanic complex. With the University of Calabria we are working on an investigation front to scientifically demonstrate this correlation, with the possibility of realizing an organic project aimed at investigating geothermal resources in the light of the new underwater volcanic complex discovered.