Italy is a land of volcanoes: spectacular but also potentially dangerous, they have always attracted man's curiosity, fascinating and intimidating him at the same time. But how many volcanoes are there in our country? How many are active? To answer these and many other curiosities, we interviewed Guido Ventura, an INGV volcanologist.
How many volcanoes are there in Italy?
in Italy we are used to considering volcanoes by referring to the most famous ones such as Etna, Vesuvius, Campi Flegrei and Colli Albani. As a consequence, many think that there are around ten Italian volcanoes. In reality we have counted as many as seventy of them, many of them are submarines and cover the seabed from Tuscany to Sicily; some are located in the Strait of Sicily, the arm of the sea that separates the island from North Africa. This number should not surprise because it is due to the particular geodynamic context in which our country is located, characterized by a so-called subduction area in which the Ionian Sea and the Adriatic Sea merge below the Apennines and the Calabro Arc and by an area in extension in which the crust thins (the Tyrrhenian Sea). The subduction and extension processes are responsible for the melting of rocks at depth and therefore for the formation of magmas. These go back to the top giving life to volcanoes. This is why the high number of Italian volcanoes shouldn't surprise us: it is the result of a typical condition of Italy and also common to high places such as Japan, the Pacific Ocean, New Zealand, where there are thousands of submarine volcanoes.
How many of these underwater volcanoes have had activity in historical times?
We know with certainty that the Marsili, which is located in the center of the southern Tyrrhenian Sea, and La Ferdinandea in the Sicilian Channel erupted in historical times while the Palinuro, located near the Calabrian coast, shows secondary volcanic activity, i.e. with low energy earthquakes and gaseous emanations. For the others, we don't actually know if and which ones are more or less active, we are carrying out research on the matter. However, we must bear in mind that with each new oceanographic campaign in the Tyrrhenian Sea we discover new volcanoes, the number is destined to grow!
How can we tell if a submarine volcano is active?
There are several methods, an example are the direct ones through which it is possible to carry out coring thus taking samples which will subsequently be dated. If, following the dating, a time range is returned to us that goes from the present to about ten thousand years ago, we can assume that they are active. Through submarine seismic stations and sampling the gases emitted, we are also able to define the state of activity of the volcano.
What do these submarine instruments consist of?
These are OBS (Ocean Bottom Seismometer) and are useful for defining the internal dynamics of the volcano, for understanding if there are fracturing processes and if these processes are due, for example, to the ascent of fluids and/or magma. In this way they give us a measure of the internal dynamics of the volcano.
And what about the volcanoes on the surface?
As it is easy to imagine working on land is easier. In Italy we have volcanoes such as Campi Flegrei, Vesuvius, Ischia, Etna and Stromboli which are absolutely among the most monitored in the world. In fact, they are equipped with permanent monitoring networks and instrumentation that allows the measurement of different geophysical, geochemical and geological parameters. In this way it is possible to study its dynamics with a certain detail.
How many volcanoes are there on the surface in Italy? Where are?
About twelve that extend from Tuscany to the Neapolitan area. In Basilicata we have Monte Vulture and in Sicily the Aeolian Islands, Etna, the Iblei Mountains and the island of Pantelleria. Even Linosa, an island belonging to the archipelago of the Pelagie Islands, in Sicily, is of volcanic origin, just as we find very ancient volcanism also on the western side of Sardinia, especially in the Campidano area. Studying this type of ancient activity is very important for understanding the evolution of the western Mediterranean.
Which ones are active?
The active volcanoes are Campi Flegrei, Ischia, Vesuvius, Vulcano, Lipari, Panarea, Colli Albani, Stromboli, Etna, Pantelleria, Marsili and Ferdinandea. Many of these are currently in a resting phase while Etna and Stromboli are characterized by an almost persistent activity.
Many are used to thinking of these volcanoes as smoking hills but is it really like that?
This is not always the case, in reality they have an extremely variable morphology. Many of these classic cones have a depression inside them, called a caldera, which is formed by the emptying of the magma chamber following large eruptions. While cones are "positive" shapes, calderas are "negative" shapes. These calderas themselves can look very different. For example, the Colli Albani caldera, near Rome, is occupied by a lake: it is the famous lake of Castel Gandolfo, also known as Lake Albano. The Iblei Mountains, a mountainous plateau of tectonic origin located in the south-eastern part of the, were in the past a partly submarine volcanic complex whose activity dates back to millions of years. Well, in this case there are no cones but fissures from which the magma came out. At Campi Flegrei instead we see a series of small cones inside a large circular caldera and each of these has given rise to one or more eruptions.
We know that volcanic earthquakes exist, how do they differ from normal earthquakes?
Volcanic earthquakes are related to the dynamics of fluids and magmas present inside the building while earthquakes in non-volcanic areas are generally related to crustal billing processes.
Finally, is it possible to predict eruptions?
Predicting a natural event essentially means establishing where it will happen, when it will happen, and with what intensity. This is what we call "hazard". For volcanoes, where it will be is relatively easy to figure out since we know where they are. As for when and what kind of eruption will happen, things get complicated. Alert levels have been established which are essentially based on monitoring data and which allow us to evaluate when a volcano enters a 'critical' state and therefore close to a potential eruption. However, each volcano has its own behavior, often not unique and therefore, as regards the type of expected eruption, monitoring data can be integrated with those based on probability estimates to evaluate the type of eruption. For some volcanoes there are also maps of exposure to different types of hazards (lava, ashes, pyroclastic flows, etc.). However, in Italy we have very advanced monitoring systems and hazard maps that allow us to evaluate and manage critical situations.