Italy is a country whose population has to live with active geological processes. Some of
these are more gradual, such as the orogenic (mountain-building) processes that have led
to the construction of the Alps and the Apenninic chain. Others, which are to be placed into
the same geodynamic framework, are more dramatic, and at times pose serious hazards
to people living nearby. These are earthquakes, flooding, landslides, and volcanoes. Of all
these, the latter constitute one of the most famous features of this country, along with good
food, a wonderful climate and a number of clichés which will not be further treated here. A
closer look reveals that the Italy's volcanoes are strikingly different. Students of geology
learn that they produce a number of highly different types of magmas, and most of them
are alkalic, which means that they contain higher proportions of chemical elements such
as potassium and sodium than many other volcanoes on Earth.
Italy is a small country, and yet it unites virtually all types of volcanoes that can be found in
other areas of the world at distances of thousands of kilometers. They represent a
constant threat to hundreds of thousands of Italians, but at the same time they bring
benefits to many more of them, such as fertile soils, favorable climatic conditions, beautiful
landscapes, and tourism. They also contributed much to the evolution of the science of
volcanology since they were easily accessible to early European scientists and other
educated persons and two of them, Vesuvius and Etna, erupted frequently when modern
science and philosophy began to evolve. But volcanology is often said to have begun
much earlier, still at an Italian volcano: Vesuvius. The devastating eruption of this volcano
in A.D. 79 was so accurately described by a young Roman, Pliny the Younger, that this
description is used in virtually all text books on volcanology. The name of its author has
also inspired to name a type of violently explosive volcanism after him: Plinian. Two other
types of volcanic activity are named after Italian volcanoes, Stromboli (Strombolian
activity) and Vulcano (Vulcanian activity). And last but not least, the word volcano itself
derives from Vulcano, which in ancient times impressed people living nearby with its thenfrequent and violent eruptions.
Why are there volcanoes in Italy? And why are they so different? Many sources say that
most Italian volcanoes are related to subduction, that is, where one plate of the earth's
crust (or better say lithosphere) is pushed under another, causing its partial melting and
thus generating the magmas that feed the volcanoes. Once one begins to read carefully in
the extensive literature that exists on the geodynamics of Italy and the surrounding region,
a very complicated picture emerges. The central Mediterranean - of which Italy is part belies the common notions about plate tectonics, the processes believed to shape the
surface of our planet. All the theories that easily explain volcanism in most parts of the
globe seem to fail to supply good arguments for volcanism in Italy. In this country, geology
is fooling the geologists.
Yet the volcanoes are there, and many of them are active or potentially active. These
volcanoes are principally linked to five different tectonic environments: subduction, backarc rifting, continental rifting, sea-floor spreading, and a fourth one that is very poorly
understood. Generally Italy's volcanism is a result of the collision of two plates of the
Earth's lithosphere (that is the solid outer portion of the planet) - the African plate to the
south, and the European (or Eurasian) plate to the north. This collision is complicated by
the complicated physical characteristics of the colliding plate margins - rather than being
homogeneous over a wide area, these are extremely heterogeneous. In some places,
there is some oceanic lithosphere left at the north margin of the African plate, which is
consumed by subduction benath the adjacent European plate. Elsewhere, no oceanic
lithosphere is left and the colliding plate margins consist entirely of continental lithosphere,
which resists subduction and rather leads to mountain building, as is the case in the Alps
and in the Apenninic mountain chain that runs along nearly all of the Italian peninsula. The
presence of rigid crustal blocks that also resist largely to mountain building (they simply do
not deform) in between the two colliding plates renders the situation more complicated. In
the case of the Hyblean-Maltese block it is believed that the counterclockwise rotation of
this block causes oblique-rifting in its rear (that is, to the southwest).
Subduction seems to be the main cause (though possibly not the only one) for the
volcanism in the Aeolian Islands - some of it is calc-alkaline, typical for subduction-related
volcanism. But the same volcanoes that have periodically produced calc-alkaline magmas
have also produced more alkalic magmas, and sometimes emitted both simultaneously,
which is not all that typical for subduction-related volcanoes. To explain this peculiarity,
some scientists have invoked a nearly vertical lithospheric slab in subduction below the
Aeolian volcanoes, which would allow the generation of calc-alkaline and alkalic magmas
at different depths and pressures at the same time. Another hypothesis places the Aeolian
Islands in an oblique-rifting context, and yet another one explains the different magmas
emitted from the Aeolian volcanoes simply with heterogeneous mantle sources below the
area.
Subduction is also assumed by some scientists to be responsible for the volcanism along
the Tyrrhenian coast of central-southern Italy (the volcanoes of southern Tuscany, Latium,
and Campania, including the Colli Albani and Vesuvius). However, these volcanoes are
even less typical of subduction-related volcanoes than their Aeolian companions; their
magmas are extremely potassic. In the past, this has been explained with the interaction of
magmas with carbonatic crustal rocks during their ascent to the surface. More recently it
has become common to favor a back-arc rifting setting for these volcanoes - while crustal
contamination of the magmas is not excluded.
In the case of the volcanoes in the Strait of Sicily (the sea channel separating Sicily from
northern Africa) the case seems to be fairly clear: continental rifting, although
geographically, the site of this rifting lies not where most people would expect it. It lies
below the sea. In the Strait of Sicily, the seafloor is constituted by continental lithosphere,
which is affected by oblique-rifting. The volcanoes born from this process are typical of
continental rift settings, because their magmas are similar to those along the Great East
African Rift. The most peculiar of these magmas are called peralkaline magmas, or
pantellerite - after the volcano of Pantelleria in the Strait of Sicily. Such magmas can
produce highly explosive eruptions but are much more fluid than, for instance, andesitic or
dacitic magmas, and can be deposited in strongly welded ignimbrites.
The massive submarine volcano of Marsili in the southern Tyrrhenian Sea seems to
resemble rather the volcanoes formed along mid-oceanic ridges, as in the Atlantic or in the
Pacific close to the western coast of the USA. Rifting is believed to have characterized the
formation of the Tyrrhenian basin when the Italian peninsula rotated counterclockwise
away from the place now occupied by Corsica and Sardinia, which once was attached to a
portion of what is now Italy.
The largest and most active volcano of Italy, Mount Etna, is also the most difficult to
explain. While one hypothesis envisages a hot-spot or mantle-plume origin for this volcano
(and also for its predecessors to the south, the Monti Iblei or Hyblean Mountains), another
places it into a certain, though indirect, relationship with subduction, and still another group
of scientists believes that asymmetric rifting along the eastern coast of Sicily allows the
uprise of magma at Etna. What seems to be clear is that the volcano lies at the
intersection of several regional fault systems, and maybe the easiest thing to assume is
that magma uprise is facilitated exactly by this tectonic situation. It must furthermore be
considered that volcanism has occurred intermittently over more than 200 million years a
few tens of kilometers to the south of Etna, in the Hyblean Mountains. Apparently there
have been persistent conditions favorable for the generation of magma in this area, which
in the same period went through different tectonic phases. It now seems almost certain
that about 1.5 million years ago, volcanism began to shift from the Hyblean Mountains
northward to arrive in the area of present-day Etna about 0.5 million years ago. The first
eruptions in the Etna area were very similar to the earlier eruptive events in the Hyblean
Mountains in that they were episodic and separated by long periods of quiescence, for the
rapid emission of voluminous lavas from regional fissures, and for the composition of the
emitted lavas. The northward shift of magmatism from the Hyblean Mountains to Etna may
have been caused by the establishment of the presently active fault systems, which
allowed uprise of magma more easily in this place than in the Hyblean area.
There is still much to be done to better understand not only the geological causes of Italy's
volcanism, but also how these volcanoes work. What is certain is that there must be very
good reasons for these volcanoes to exist, because they are there. In a period when wellestablished concepts in geology are subjected to serious doubt and criticism from an evergrowing number of scientists (take, for example, the mantle plume debate), geology is
destined to live through a new period of intense growth and constructive discussion and far
from having all the answers to pressing questions. Italy is one of the places where this is
most evident, and where further progress in science is most necessary.
Italian volcanoes presented on this site:
The characteristic silhouette of Stromboli volcano with its persistent gas plume seen from a passing hydrofoil
in June 1997. View is to from the east. The gas plume is clearly seen to be rising from a place below the
summit - the active craters actually lie in a large depression formed by no less than four large sector
collapses during the past 13,000 years, and have not yet built up to the height of the old summit. The
growing slope of the active cone is known as the Sciara del Fuoco. Since the craters lie in a confined
depression, much of the island is protected from invasion by lava flows, although larger eruptions may
discharge pyroclastic flows and heavy tephra falls over all of the island. The steep slope of the Sciara del
Fuoco is unstable and prone to collapse; a relatively small collapse at the end of December 2002 triggered a
small tsunami that caused considerable damage in the village of Stromboli, seen at the left base of the
volcano
Stromboli Volcano, Italy
volcano number: 0101-04= (according to Volcanoes of the World, 1994 edition)
summit elevation: 924 m (or 926 m)
location: 38.789°N, 15.213°E
Introduction
The "normal" activity of Stromboli consists of discrete small explosions that eject glowing lava fragments a
few tens of meters high. This is known as "Strombolian" activity and applied worldwide to eruptions of this
type. These photographs show night (top) and daylight (bottom) views of Strombolian activity at a small cone
built up within one of the summit craters of Stromboli.
22 August 1994
Stromboli is one of the few volcanoes on earth that display continuous eruptive activity (also called
"persistent" activity) over a period longer than a few years or decades. Its historic record goes back to more
than 2500 years before present, and there is evidence that its persistent activity has been going on for as
long as 5000 years (recent studies, however, indicate that this activity began only during the first millennium
A.D.).
Most of this activity is of a very moderate size, consisting of brief and small bursts of glowing lava fragments
to heights of rarely more than 150 m above the vents. Occasionally, there are periods of stronger, more
continuous activity, with fountaining lasting several hours, violent ejection of blocks and large bombs, and,
still more rarely, lava outflow. Twice during the 20th century (in 1919 and 1930) there have been large
eruptions that caused significant damage and killed persons even at considerable distance from the craters.
Several explosions in the past few years have surprised groups of tourists who were in the summit area,
causing various accidents as people began to run around in fear and consternation. Unfortunately, one
person was killed by such an event in late 2001. Pure luck has prevented that tourists were in areas at risk
when the volcano entered into a serious eruptive crisis at the end of 2002, and when a very powerful
explosion occurred on 5 April 2003.
Eruptions that produce lava flows occur at very irregular intervals that may vary from a few years to more
than 15 years. The most recent of these eruptions occurred in 1975, 1985-1986, and 2002-2003. Generally
such eruptions are considered rather harmless, because lava flows remain confined to a large depression
formed during several sector collapses during the past 13,000 years, which hosts the active craters.
However, the 2002-2003 eruption was accompanied by a landslide, which triggered a tsunami (a large wave
caused by the displacement of large rock volumes below the sea or avalanches into the sea). As a
consequence, the portions of the main village on the island closer to the coast suffered substantial damage,
and for the first time in history the entire population of the island was evacuated.
Although it has been visited almost daily by numerous people in the past thirty years or so, documentation of
the activity of Stromboli has been far from complete until very recently. Thus, as recently as August 1994, the
emission of a small volume of lava from the northernmost of Stromboli's presently three craters was only
revealed several months later. The volcano is now being monitored visually by several automatic
telecameras maintained by the Catania section of the Istituto Nazionale di Geofisica e Vulcanologia (INGV)
whose task is the surveillance of seismic and volcanic activity in Sicily. Seismic stations are maintained by
the monitoring network of the INGV and several other institutes such as the Dipartimento di Georisorse e
Territorio of the University of Udine. These stations are continuously transmitting data to those institutes.
However, as surprisingly as this might seem, much of the eruptive dynamics of Stromboli are still not fully
understood, and there is a pressing need to further research on the way this volcano works. The complex
events during the major effusive eruption of 2002-2003 have been a serious challenge both for scientists and
civil defense personnel.
These Stromboli pages will give some general information about the volcano and deal with some specific
aspects of its recent eruptive history. Particular attention is devoted to the period since 1985 which includes
many personal experiences by myself, and which has proved to be the best documented period in the history
of Stromboli. As you will note these pages are densely interwoven with those of the companion site
"Stromboli On-line", as both "Stromboli On-line" and "Italy's Volcanoes" are intended to complement each
other.
A guide to the Stromboli pages
The first part of the Stromboli section introduces you to the geographical setting of the volcano, with
information on the location and morphology of the island. From there you may proceed to the geological
evolution of the volcano, which is anything else than simple. The eruptive activity during the historical period
is reviewed on a number of pages, starting with a simple list of the major eruptive events known during that
period, and then showing a series of photos taken on the volcano before 1930, a critical year during the
recent history of the volcano. The powerful and destructive eruption of 1930 is described in detail, followed
by an overview of the activity between 1930 and 1985. The ten years from 1985 to 1995 are then dealt with
in much detail, including eyewitness accounts from myself and many others, numerous photos, and an
analysis of the morphological changes caused by the eruptive activity. Activity after 1995 is described in a
more synthetic manner on another page.
The final part of the Stromboli section talks about volcanic hazards, an aspect of studies on the volcano
which is receiving increasing attention due to the growing number of visitors to the island, and following
studies on violent eruptions in the not-too-distant past. This also includes a discussion of the way tourism is
handled at the volcano in the light of numerous episodes of strong explosive activity in the past few years.
The interested visitor will finally be guided to further reading and a selection of web sites about Stromboli.
Extensive cross-links to Stromboli On-line are provided throughout these pages. To return to these pages,
use the "Back" button of your web browser.
Mount Etna
Tectonic setting and geological evolution
Sketch map of eastern Sicily showing location of Etna and other important structural elements of the
geology of the region. Faults are shown in black; the volcanics of the Hyblean Plateau (Monti Iblei) are
shown in pink color.
The late 1950's and 1960's have seen the advent of the concept of Plate Tectonics which is
now generally accepted and appears to explain neatly a vast range of geological phenomena of
the past and the present. In this framework, volcanism is basically associated with three
tectonic processes:
1. Subduction. Where the margins of two lithospheric plates - one oceanic, the other
2.
3.
continental - collide, the denser, oceanic plate is thrust (=subducted) under the lighter
continental one. Magmas are generated by the partial melting of subducted oceanic
lithosphere (that is, the rigid outer stratum of the globe), which consists of basalt
covered by mainly silicic sediments (which contain large quantities of water), and the
resulting magmas have a high silica content because much of the melt is constituted by
the sediments. Almost all volcanoes around the Pacific Ocean (the so-called "Ring of
Fire") are the result of subduction processes, and their activity is highly explosive.
Rifting. This occurs in areas where the Earth's crust is torn apart, allowing magma to
rise to the surface. Most of this activity occurs in the ocean basins, the most famous
example being the Middle Atlantic Ridge where two lithospheric plates are "drifting"
apart, and new crust is formed by the emission of basaltic magmas. Only in a few
places, mainly Iceland and the Afar region in northeastern Africa, rifting, which
generates oceanic lithosphere, is occurring on land.
Hot Spots. In various places on Earth magma is rising from the Upper Mantle to the
surface where there are no plate boundaries (like in the previous two cases), and
magmatism of this type is called "intraplate magmatism". The places where this occurs
are known as "hot spots" which appear to occupy relatively fixed positions in space
while lithospheric plates move across them. Magma is being fed by so-called mantle
plumes. The result is a long-lived volcanism which often builds a chain of volcanoes
which become progressively older with distance from the active hot spot. Volcanoes
related to this type of process occur both on oceanic and continental lithosphere. The
most famous examples are the Hawaiian islands, with the currently active volcanoes of
Mauna Loa, Kilauea, and Loihi.
Etna apparently does not fit into any of these tectonic settings. Subduction is believed to have
contributed to the volcanic activity in the Aeolian Islands, off the northern coast of Sicily, but
recently proposed hypotheses envisage a peculiar type of rifting as another factor acting
simultaneously in the same area. Etna is not directly related to the Aeolian volcanism. To
understand what may be the reason for the long-lived and voluminous volcanic activity at
Etna, one has to get familar with the complicated structural situation of the area, and in the
following I will try to render an idea as comprehensive as possible of that situation.
The following text (from Behncke 2001) is a modified excerpt from the book "The
Southern Appennines: Anatomy of an Orogen" (edited by G. Vai and P. Martini) which
was published by Kluwer Academic Press in late 2001.
"Etna, Europe's highest (3310 m as of early 2002) and most active volcano, lies in a
structurally highly complex, and not yet fully understood, setting which is reflected in the
abundance and variety of - often controversial - models proposed for the volcano and its
tectonic environment. Recently proposed hypotheses envisage as critical factors facilitating the
uprise and eruption of magma: (1) dislocation between the "Malta-Sicilian block" and the
Ionian basin (Gillot et al. 1994) in the framework of an asymmetric rifting process (Continisio
et al. 1997); (2) extensional tectonics leading to the formation of a graben in the Catania Plain
(Di Geronimo et al. 1978); (3) location of Etna at the intersection of a number of major
structural lineaments (the most important being the Malta Escarpment and the MessinaGiardini fault zone; McGuire et al. 1997); (4) dilatational strain on the footwall of an eastfacing normal fault in the Siculo-Calabrian rift zonewhere WNW-ESE-directed regional
extension takes place (Monaco et al. 1997); (5) a hot spot (Tanguy et al. 1997; Schiano et al.
2001); (6) rollback of the lithospheric slab that is subducted below the Tyrrhenian Sea
(Gvirtzman and Nur 1999) or magma ascent through a "slab window" (Doglioni et al. 2001).
On the other hand, Lanzafame et al. (1997) postulate N-S-directed compressional tectonics
affecting the southern part of Etna. This picture is further complicated by the effects of the
presence of the voluminous Etnean edifice on the regional stress field, exerted both by the
load of the volcano and by the movement of magma below and within it. Thus, volcanism and
tectonics at Etna are clearly interacting, although the problem of cause and effect remains to
be solved.
"Activity in the Etnean area began about 0.5 Ma (million years) ago with the emission of
tholeiitic magmas in a submarine and coastal environment that crop out on the coast to the
north of Catania (Acicastello, Acitrezza) and was followed at around 0.3 Ma by another episode
of tholeiitic volcanism in the SW sector of Etna. Beginning about 170 ka (thousand years) ago,
mafic alkaline magmas were emitted to form several eruptive centers (Ancient Alkalic Centers;
Romano 1982) and possibly the first major Etnean edifice (Ancient Etna of Gillot et al. 1994,
including the Calanna and Trifoglietto I centers) before the magmas became more evolved,
leading to more explosive volcanism and the construction of a succession of volcanic edifices
with alternating pyroclastic and effusive products, which has been comprehensively named
Trifoglietto. The major eruptive centers of this unit are Trifoglietto II, Vavalaci and Cuvigghiuni
(Gillot et al. 1994).
"Another series of major volcanic edifices grew, and partially were destroyed, by caldera
collapse, during the Mongibello stage which is commonly subdivided into the Ancient and
Recent Mongibello. The earlier includes the Ellittico and Leone volcanic centers and formation
of the homonymous calderas, and eruption of the most evolved (trachytic) magmas during the
history of Etna, while the latter comprises the construction of the modern summit cone which
was interrupted at least once by caldera collapse (Piano caldera, about 2 ka). The result of this
eventful history is a highly complex edifice whose morphology is that of an asymmetric shield
volcano topped by a stratocone and whose eastern flank hosts the Valle del Bove, a vast
caldera depression formed during successive collapse events beginning during the late
Trifoglietto stage and continuing through the Holocene. Much of the stratigraphic information
regarding the growth of the various eruptive centers has in fact been gained from the walls of
the Valle del Bove."
References
Behncke B (2001) Volcanism in the Southern Apennines and Sicily. In: Vai GB and Martini IP
(eds) Anatomy of an orogen: the Apennines and adjacent Mediterranean basins. Kluwer
Academic Publishers, Dordrecht-Boston-London: 105-120 (Etna: pp. 111-113).
Continisio R, Ferrucci F, Gaudiosi G, Lo Bascio D and Ventura G (1997) Malta escarpment and
Mt. Etna: early stages of an asymmetric rifting process? Evidences from geophysical and
geological data. Acta Vulcanologica 9: 45-53.
Di Geronimo I, Ghisetti F, Lentini F and Vezzani L (1978) Lineamenti neotettonici della Sicilia
orientale. Memorie della Società Geologica Italiana 19: 543-549.
Doglioni C, Innocenti F and Mariotti G (2001) Why Mt Etna? Terra Nova 13: 25-31.
Gillot PY, Kieffer G and Romano R (1994) The evolution of Mount Etna in the light of
potassium-argon dating. Acta Vulcanologica 5: 81-87.
Gvirtzman Z and Nur A (1999) The formation of Mount Etna as the consequence of slab
rollback. Nature 401: 782-785.
Lanzafame G, Neri M, Coltelli M, Lodato L and Rust D (1997) North-south compression in the
Mt. Etna region (Sicily): spatial and temporal distribution. Acta Vulcanologica 9: 121-133.
McGuire WJ, Stewart IS and Saunders SJ (1997) Intra-volcanic rifting at Mount Etna in the
context of regional tectonics. Acta Vulcanologica 9: 147-156.
Monaco C, Tapponnier P, Tortorici L and Gillot PY (1997) Late Quaternary slip rates on the
Acireale-Piedimonte normal faults and tectonic origin of Mt. Etna (Sicily). Earth and Planetary
Science Letters 147: 125-139.
Tanguy J-C, Condomines M and Kieffer G (1997) Evolution of the Mount Etna magma:
Constraints on the present feeding system and eruptive mechanism. Journal of Volcanology
and Geothermal Research 75: 221-250.
More on the geological evolution of Etna
http://boris.vulcanoetna.com/