One area we have mostly stayed away from in this blog is volcanism around Italy. There are many reasons, most of them having to do with a whole boatload of actual experts doing actual science in the region, meaning there is a firehose of new information flow about volcanoes, earthquakes and tectonics from those experts going on all the time. Thrashing our way through that flow of great science and the mountain of papers published previously is somewhat daunting.
But Italy is important. It is a full-featured volcanic region, complete with an active supervolcano / restless caldera (Campi Flegri) populated by over 3 million, multiple active landside volcanoes (Vesuvius, Vulcano, Stromboli, Etna), a massive active stratovolcano (Etna) sitting on top of a plate tear, a line of recent calderas along the central west coast of Italy, and layer upon layer of massive ignimbrite, tephra, and ashfall deposits associated with those systems. There is even an active oceanic volcanic arc in the Aeolian Islands.
It has given us names that define the business of volcanoes: Somma, Vulcano, Stromboli, Plinian, Solfatara, among others. It is the site of the first modern description of a major eruption, that of Vesuvius in 79 AD, by Pliny the Younger.
As an active tectonic region, it is highly earthquake prone. Local buildings are a mix of very old structures hundreds to thousands of years old to relatively modern ones. And the buildings constructed of stone and masonry do not do well in larger quakes. OTOH, Roman concrete made with volcanic ash is very tough and lasts a long time, especially in seawater.
So where does all this activity come from? Specifically, why here?
Tectonics in Italy are driven by the ongoing collision between the African and European Plates. In the Mediterranean, this has been a lengthy and complex process creating the Alps, which originally extended all the way down the Iberian (Spanish) Peninsula. The second mountain range runs the length of Italy called the Apennines. These were built by the ongoing collision.
Tectonics of the eastern Mediterranean is quite complex with multiple platelets jostling in the region. To the far east, we have the Anatolian Plate (generally Turkey) being squeezed to the west by the ongoing collision into another platelet / micro plate the Aegean Sea Plate (essentially southern Greece and the Aegean Sea). The Aegean Plate is moving generally SW. The next platelet to the west is the Adriatic Plate. It runs the length of Adriatic Sea, curving down and around the end of Italy and the southern boundary of Sicily. This platelet is subducting under the main portion of the Eurasian Plate forming the Apennines and powering much of the volcanic activity and tectonic activity in Italy. Final platelet is the Ionian to the SE of the Adriatic platelet. The Ionian platelet is subducting under the Adriatic platelet in the vicinity of Sicily and the southern end of Italy. This complex collision has been taking place for tens of millions of years.
As with any complex tectonic region with multiple micro plates / platelets jostling, the farther back in time, we try to go, the less clear what was happening becomes. While the move of Africa into southern Europe has been taking place since the early Cretaceous, the vectors and rates of original motions is not well known. What we do know is that a major change in convergence rates took place in the Eocene when the convergence rate almost stopped, and the direction changed to N-NW. Around this time the microplates started rotating as they jostled against one another. The Adriatic platelet may have originally belonged to Africa but is now viewed as an independent microplate in the collision zone.
The Alps were built by a thick thrust-fold belt as the Adriatic platelet overrode the European Plate and created a vast fold and thrust belt of mountains. The Apennines were built by steep subduction of the Adriatic platelet under Italy. This subduction was so steep that plate rollback beneath Italy is thought to be taking place. In the bend around the southern end of Italy and Sicily, there is a tear in the subducting slab thought to be the location that mantle fluids are currently powering volcanism in Sicily including Etna.
There was a sharp increase in igneous activity around the Alps 33 – 29 Ma, with emplacement of multiple plutons of magma from mantle and hybrid mantle-crustal sources likely powered by dehydration of the European subducting continental segment of the slab or a possible slab detachment. Most eruptive volcanic activity was confined to Sardinia, though there was minor activity in the Apennine foreland some 30 Ma.
The Apennines are described as an accretionary wedge along the subduction hinge of the Adriatic and Ionian microplates. The subduction hinge has moved some 700 km E over the last 23 Ma via slab rollback. This eastward move also moved volcanic activity eastward from Sardinia – Corsica starting 38 Ma, some 10 Ma after subduction started. This also created an extensional basin that became the Tyrrhenian Sea.
The Sardinia – Corsica Block rotated a bit counterclockwise as the subduction hinge migrated eastward. As that rotation ended 15 Ma, the eastern extensional margin shifted SE, as did the volcanic activity. Volcanic activity migrated eastward from Corsica 10 – 5 Ma and also started at Etna. By 5 – 3 Ma, volcanic activity migrated southward along the coast toward the Roman region. Major volcanic activity broke out from the Roman Province over the course of the last 1 Ma.
Crustal thickness in the middle of the Tyrrhenian Sea basin is less than 10 km and there is significant volcanic activity particularly in the SE part of the newly formed basin. There are active seamounts and volcanic islands present today. N and NE of Sicily are seven major volcanic islands (Aeolian Islands), a large number of volcanic seamounts, all active from 1.3 Ma. They are located on a 15 – 20 km thick continental crust above a steeply dipping crustal plate segment. There are numerous other younger volcanic islands in the Sicily Channel with new activity taking place.
While Etna is located close to the southernmost Aeolian Islands, it is erupting completely different volcanic products, which in turns means different magma sources. Etna is thought to be situated above a slab window created by differential rollback of the subducted Ionian oceanic Plate, essentially creating a tear in the subducted slab.
Anorogenic (non-subduction related) magmatism in the entire region took place in two windows – 65 – 21 Ma and 12 Ma – present, with a hiatus 51 – 12 Ma. Orogenic (subduction related) magmatism is concentrated in three periods: 33 – 27 Ma in the Alps, 22 – 18 Ma in Sardinia, and over the last 2 Ma along peninsular Italy, SE Tyrrhenian Sea (Aeolian Islands) and Sicily.
Sicily (7 Ma – present) – Etna, Iblei, Istica, Pantelleria, Linosa, Sicily Channel seamounts. Stratovolcanoes, diatremes, small plateaus, cinder cones, tuff cones, tuff rings. Active volcanism at Etna and the Sicily Channel.
Sardinia (12 Ma – 0.1 Ma) – Isola del Toro, Capo Ferrato, Moneiferro, Orosei – Dorgali, Monte Arci, Logudoro. Stratovolcanoes, basaltic plateaus, monotenetic centers.
Southern Tyrrhenian Sea Floor (7 – 0.1 Ma) – Maghaghi, Marsili, Vavilov, Aceste, Prometeo, at least 3 other sites. Seamounts and lava fields.
All listed volcanoes were active at some point in the timeframe listed for each region.
Tuscany Region (8.5 – 0.3 Ma) – Acid intrusions at Elba, Montecristo, Giglio, Campiglia, and Lardello – Amiata. Acid lavas at San Vincenzo, Roccastrada, Amiata, Cimini, and Tolfa – Cerite – Manziana. Multiple mafic centers at Carraia, Elba, Orciatico and Montecatini, Radiofani, Cimini, Torre Alfina. Mainly felsic rocks. A few ignimbrites. No pyroclastic rocks in most centers.
Intra-Apennine Province (600 – 300 ka) – San Venanzo, Cupaello, Polino, Axquasparta, Oricola. Monogenetic pyroclastic centers and rare lavas.
Roman Province (800 – 6 Ka) – Vulsini, Vico, Sabatini, Alban Hills. Large, multicenter volcanic complexes with stratovolcanoes, calderas formed by pyroclastic rocks and minor lavas.
Ernici / Mid-Latin Valley (700 – 100 ka) – Emici, Pofi, Ceccano, Particia, Roccamonfina. Monogenetic pyroclastic and lava centers. Roccamonfina is a stratovolcano with a central caldera and intra-caldera domes.
Campania (400 ka – present) – Somma – Vesuvius, Campi Flegri, Ischia, Procida, Ponza, Palmarola, Santo Stefano, Ventotene, unnamed buried calc-alkaline volcano. Stratovolcanoes and multicenter complexes mostly of pyroclastic and minor lavas. Rhyolitic lavas and pyroclastics at Ponza and Palmarola.
Vulture (700 – 100 ka) – Vulture and Melfi. Stratovolcanoes with summit caldera, intracaldera maars, some parasitic centers. Dominant pyroclastics and lavas.
Aeolian Arc (270 ka – present) – Alicudi, Filicudi, Salina, Vulcano, Lipari, Panarea, Stromboli. Large stratovolcanoes with some calderas. Alternating pyroclastics and lavas. Active volcanism in central – eastern portion of the arc.
Southern Tyrrhenian Sea Floor (12 Ma – present) – Cornacaya, Anchise, Sisfo, Enarete, Eolo, Lametini, Alcione, Palinuro, Marsili Sites. Seamounts of various ages, shapes and volumes. Marsili is a 60 km long ridge rising 3 km above actively spreading Marsili Basin.
Individual Volcanoes and Eruptions
While activity in Italy has been robust over the last million years, I wanted to touch on a few notable systems.
Campi Flegrei, aka the Phlegraean Fields. This is the resident active supervolcano in Italy. The earliest known eruption took place 47 ka. The 13 km diameter caldera was formed in two explosive eruptions 36 ka and 15 ka. The first produced the massive Campanian ignimbrite. The second produced the 79 km3 Neapolitan Yellow Tuff. The Campanian Tuff eruption was classed as a VEI 7.5, producing over 320 km3 bulk volume of material, the most explosive eruption in Europe in the last 200 ka. There have been numerous subsequent eruptions from widely scattered satellite subaerial and submarine vents, 10 in the last 10 ka. The most recent eruption took place in 1538. This is officially classified as a restless caldera.
The Alban Hills (Colli Albani) is a volcanic complex SE Rome. A large stratovolcano is topped with a 10 x 12 km caldera. Seven major eruptions 560 – 350 ka ejected over 280 km3 of material. Subsequent eruptions built a new central cone in the caldera and formed multiple phreatomagmatic craters in the caldera and on its flanks. The largest of these is the 2.5 x 4 km Lake Albano. There have been recent seismic swarms.
Roccamonfina is a large stratovolcano at the northern end of the Campanian Plain north of Naples. It is topped with a 6 km diameter caldera. It produced multiple eruptions 440 – 227 ka, with the largest a VEI 6 producing nearly 14 km3 bulk volume Upper White Trachytic Tuff. Activity proceeded in three stages. Initial activity was widespread volcanic activity in a 1,000 km2 area. Effusive active concentrated in a central location building a volcanic cone. There was a sector collapse some 400 ka that formed a depression creating a lake. This was followed by explosive eruptions from the caldera. Historic activity mostly stopped nearly a quarter million years ago.
Monte Vulture is an extinct stratovolcano located mostly E of Naples. It is unique because it is located to the east of the Apennines and the volcanic arc in Italy. It is a stratovolcano topped with multiple calderas that has produced parasitic cones and pyroclastics covering 150 km2. The system was active starting 1 – 0.8 Ma. This included ignimbrite eruptions and dome emplacement. Cone-building and caldera eruptions took place until around 330 ka. This included creation of at least two small calderas and a possible flank collapse creating an amphitheater. The younger caldera is 3 km in diameter. Most recent activity 130 – 40 ka created two intra-caldera maars.
Marsili is a large seamount in the Tyrrhenian Sea, 175 km S of Naples, 80 km N of the Aeolian Arc volcanoes. It tops out 3,000 m above the sea floor, 450 m below sea level. It is one of the largest volcanoes in Europe and measures 70 x 30 km. Activity on it may date back 1 Ma, though the Wiki writeup on it suggests 200 ka. Granyia covered this seamount and its potential for collapse in 2018. There is ongoing hydrothermal activity and shallow volcano-tectonic seismicity associated with this system.
Last, but certainly not least is Etna. Etna is a massive stratovolcano located in Sicily. It is built on an older structure and is today 3,326 m tall, covering an area of nearly 460 km2. It has been active for most of the last 500 ka. It does have a history of past explosive eruptions 35 – 15 ka, producing large pyroclastic flows and extensive ignimbrite deposits. Ash from these eruptions can be found up to 800 km N. A flank collapse into the ocean some 8 ka produced a tsunami in the Eastern Mediterranean. This created a 5 x 10 km amphitheater open to the E on its flanks. The most recent flank collapse is thought to have taken place some 2 ka, creating a smaller amphitheater that has been mostly refilled with more recent lava flows. Today, it mostly erupts basalts, andesites, and trachyte variants in explosive and effusive eruptions.
As with other complex tectonic regions, Italy is quite earthquake prone. Like most regions with older buildings, the larger quakes are generally deadly as older structures are not built to modern earthquake prone standards. A M 6.2 om 2016 killed nearly 300, injuring hundreds more. There have been over 400 destructive earthquakes over the last 2,000 years documented in Italy. There have been 15 major earthquakes since 1905, the most powerful of which was a M 7.1 in 1908 that took 70,000 lives.
Generally, earthquakes don’t get much larger than M 7.1 – 7.2, though those in the M 6+ range are relatively common.
Italy is a complex and active volcanic – tectonic region with multiple large, dangerous, currently active volcanic systems (Etna, Vesuvio, Campi Flegrei, Marsili). There is active seamount construction underway in the Tyrrhenian Sea and in the Sicily Strait. Volcanic activity along the western coast of continental Italy is relatively recent and prolific. The problem with all of this are the people living right underneath or on top of the active volcanic systems. A secondary problem is the large population of buildings that tend not to tolerate seismic movement all that well (though the ancient ones seemed to so far). A truly fascinating, albeit dangerous region.