The volcanism of Italy is due chiefly to the presence, a short distance to the south, of the boundary between the Eurasian Plate and the African Plate. Italy is a volcanically active country, containing the only active volcanoes in mainland Europe (while volcanic islands are also present in Greece, in the volcanic arc of the southern Aegean). The lava erupted by Italy's volcanoes is thought to result from the subduction and melting of one plate below another.
Three main clusters of volcanism exist: a line of volcanic centres running northwest along the central part of the Italian mainland (see: Campanian volcanic arc); a cluster northeast of Sicily in the Aeolian Islands; and a cluster southwest of Sicily around the island of Pantelleria, in the Mediterranean's Strait of Sicily. Sardinia has had a totally separate geological history from that of the rest of Italy, where several cycles of volcanic activity occurred, the last of which ended at the beginning of the Pleistocene, but currently hosts only permanently extinct volcanoes.[1]
Due to their position within densely populated areas, Etna and Vesuvius have been included in the list of "Volcanoes of the Decade", a global list of volcanoes to be kept under closer surveillance.[2] In particular, the "Volcanoes of the Decade" is a list drawn up by International Association of Volcanology and Chemistry of the Earth's Interior, as part of a United Nations project, which includes, overall, 16 volcanoes distributed all over the world.[2]
Italy was the first country to exploit geothermal energy to produce electricity.[3] The high geothermal gradient that forms part of the peninsula makes it potentially exploitable also in other regions; research carried out in the 1960s and 1970s identified potential geothermal fields in Lazio and Tuscany, as well as in most volcanic islands.[3]
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Four of Italy's volcanoes have erupted in the last one hundred years:
At least 10 other volcanic centres have seen eruptions in historic times. In order of the most recent eruptions, they are:
In addition to the volcanoes on land, there are three submarine volcanoes in the seas surrounding Italy, in particular in the south-eastern Tyrrhenian and in the Strait of Sicily:
In Italy there is also a large number of geological structures due to extinct volcanic centres. It is possible to group these volcanoes into various categories:
The volcanic system of Somma-Vesuvius is generally characterized by explosive eruptions. The most widely-known is the one that destroyed the Roman cities of Pompeii, Herculaneum, Stabiae and Oplontis in 79 AD, causing thousands of victims. It is estimated that this eruption had a Volcanic Explosivity Index (VEI) equal to 5, and is considered the archetype of Plinian eruptions, which are named after Pliny the Younger, an eyewitness of the event.[30][31]
Scholars have discovered that previously Vesuvius had given rise to even more violent Plinian eruptions,[32] the last of which was that of the pumice of Avellino about 3,900 BP (estimated to have a VEI of 6). After 79 AD there were no more plinian eruptions, but at most sub-plinian. The most important were that of 472 AD[33] (whose ash reached Constantinople) and that of 1631, which killed thousands of people (due to pyroclastic flows and lahars),[34]) and which was taken as a reference by Protezione Civile for the drafting of evacuation plans in the event of future eruptions.[35] Due to this eruptive history, and the very high population density in the Metropolitan City of Naples, Vesuvius is considered one of the most dangerous volcanoes in the world.[36]
Unlike Vesuvius, the nearby Phlegraean Fields are not made up of a single large volcanic edifice, but are a vast volcanic field within which numerous eruptive vents have opened, often different from eruptions.[37] The only eruption in historical times, which generated Monte Nuovo and Lake Avernus, was of low intensity, and was preceded by a period of quiescence that lasted more than 3,000 years (before which there was a long sequence of close eruptions).[38] However, the Phlegraean Fields are capable of producing violent eruptions, which earned them the title of supervolcano.
The most famous was that of the Campanian Ignimbrite eruption, which occurred about 40,000 BP, considered the most severe ever to occur in the Mediterranean area, having a VEI equal to 7, and which probably had effects on the climate worldwide.[39] Only slightly less intense was that of the Neapolitan yellow tuff, which occurred about 15,000 BP.[40] There are also indications of a third large-magnitude eruption, which probably occurred 29,000 BP.[41] For this reason, the Phlegraean Fields are also closely monitored by the Vesuvius Observatory.
They are also characterized by numerous secondary volcanic phenomena, of which the best known is the Phlegraean bradyseism, which in the second half of the 1900s led to the evacuation of entire districts of the city of Pozzuoli.
Etna is characterized by an almost continuous eruptive activity, and, unlike Vesuvius, the eruptions of Etna tend to be effusive, with lava flows that can come from both the summit craters and side openings. These eruptions almost always do not cause high damage, but there are exceptions. The largest effusive eruption of Etna in historical times took place in 1669, when the lava buried numerous villages reaching the sea near Catania, with a flow up to 17 km long. This eruption completely changed the landscape of the area, but due to its effusive nature there were no victims associated with the eruption.[42]
Another eruption of similar magnitude occurred in 396 BC, when the lava flows, reaching the sea, hindered the advance of the Carthaginian army of Himilco during the Greco-Punic wars (as described by Diodorus Siculus).[43] A few dozen deaths were recorded in Bronte in the eruption of 1843, due to a phreatic explosion due to contact between the lava and a source of water. The last highly destructive eruption occurred in 1928, when the lava buried the town of Mascali.[44] In the 1979 eruption, a sudden explosion caused nine deaths and 23 injuries in a group of tourists on excursion, and in that same eruption the last official order to evacuate an inhabited centre was issued due to an eruption of Etna.[45]
The great explosive eruption of 122 BC, a Plinian event, which caused serious damage to the Roman city of Catania, which for this reason was exempt from paying taxes to Rome for a decade, was completely different. A further explosive eruption, of a sub-Plinian type, occurred in 44 BC. This eruptive history, associated with the high population density of the Metropolitan City of Catania (but with a less problematic situation than that of Naples), therefore requires continuous surveillance of the volcano.
Stromboli is one of the most active volcanoes in the world, with almost persistent activity for at least 2,000 years, which is why it was nicknamed the "lighthouse of the Mediterranean". Usually this activity consists of a continuous degassing, interspersed with small bursts of low intensity, at temporal distances that can vary from a few minutes to a few hours, a type of eruption that is defined precisely as Strombolian.[6]
About 1–2 times per decade, lava can overflow from the summit craters, forming flows that can also reach the sea. These flows usually go towards the north-western area of the island, in the so-called Sciara del Fuoco (a depression shaped like a horseshoe, formed about 6,000 BP,[46]) away from the inhabited settlements. At irregular intervals, Stromboli can give rise to much more violent explosions than normal, called paroxysms,[47] which can instead cause damage to the population.
On 11 September 1930, what is considered the most violent eruptive event of the volcano in the last 13 centuries,[48] occurred with a massive fallout of volcanic material on the inhabited centre of Ginostra and the formation of a pyroclastic flow outside the Sciara del Fuoco. In total, there were four deaths and numerous buildings destroyed. The most recent paroxysmal events occurred on 3 July and 28 August 2019,[49] with the former explosion causing the death of a hiker.[50] In these eruptions, pyroclastic flows able to flow over the sea for a few hundred meters have also been observed.[51]
A further source of danger about Stromboli is the risk of landslides (often in correspondence with the paroxysms), both aerial and submarine, capable of causing tsunami waves. The last event of this type occurred on 30 December 2002, when the wave did damage to coastal buildings.[52] An underwater landslide event of greater proportions could have caused the tsunami in the Gulf of Naples in 1343.[53]
