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FAQ 01.
When will Etna erupt again? 1. When will Etna erupt again? Top This is one of the questions most difficult to answer, even after the flank eruption of the summer of 2001 - although the answer has two parts, the first of which is quite simple. In fact, Etna is in eruption almost continuously, but for long periods this activity is confined to the summit craters and nearby eruptive fissures, and merely represents the steady-state output of the volcano (which, however, undergoes significant fluctuations). If "eruption" is understood as the opening of new vents and lava emission on the flanks, then the answer is: no one knows for sure. Unfortunately, volcanoes usually do not behave in a strictly regular manner in terms of their eruption frequencies, and they may often change the behavior manifested for a certain period (take Vesuvio (Vesuvius) which was in virtually constant eruption for three centuries until 1944, but has been completely inactive since then). At Etna, between 1971 and 1993 there were 13 well-defined flank eruptions, an average of one eruption every 1.7 years (since 1993, that is, during the past 7 years, there has been none). Usually these flank eruptions were preceded by activity at the summit craters; in some cases there were real cycles of summit activity followed by flank eruption (e.g. 1988-1989). When the summit craters resumed activity in 1995, it seemed that another cycle had begun, and a flank eruption would occur within a few months to a few years. However, this time the summit eruptions lasted 6 years before there was another flank eruption. The eight years which passed between the flank eruptions of 1991-1993 and 2001 were the longest interval without flank activity since 1971. This did not mean that the volcano was "less active", or that the magma supply had dropped. The volcano inflated, recovering more than twice the inflation lost during the large 1991-1993 eruption. Intense seismic activity in various sectors of the mountain indicated magma movements at depth, in some instances approaching quite close to the surface. Etna was recharging with magma, but it appears that its internal plumbing system was (at least until July 2001) more stable than it was from 1971 until 1993. After the summer 2001 eruption everybody is wondering how long it will take until there will be the next flank eruption. There are several possibilities how Etna will behave in the near future: 1) there will be another long period of summit activity. 2) a new eruption will occur somewhere on the flanks on the volcano. 3) the activity will eventually die down. So we know that a flank eruption will certainly occur in the future, but at this moment neither the time nor the location and character of that outburst can be foreseen. However, a few assumptions based on Etna's past and recent behavior can be made. The two major fracture systems (or rift zones) on the northeastern and southern to southeastern flanks are more prone to eruption than the other sectors of Etna: 18 out of the 23 flank eruptions in the 20th century as well as the 2001 eruption have taken place in these areas. Before and during the 2001 eruption an extensive fracture system developed from the NE to the S flank where all eruptive fissures of this eruption became active. It may well be that this fracture system remains unstable, so that the easiest pathways for magma can be found there, and thus the next flank eruption might affect more or less the same sectors of the volcano. The destructive potential of a flank eruption is determined by three factors: the location of the eruptive vents (on which side of the volcano and at what elevation), the mass eruption rate and, to a lesser degree, the duration of the eruption. If, for example, an eruption were to occur in the Monte Palestra area on the western flank where much of the recent seismicity has been concentrated, the lava flows would essentially destroy forest and interrupt dirt roads; in the worst case they would overwhelm one or two of the simple mountain refuge huts in the Etna Natural Park. Only if the mass eruption rate is exceptionally high, the lava flows will manage to cover the distance to the nearest inhabited areas (Bronte and Adrano) which lie some ten km downslope, and there is much space between the towns in that sector. On the other hand, a high-effusion rate eruption on the southern or southeastern flank would pose an enormous threat to the densely populated areas in that sector. In that case, an important controlling factor would be the eruption's duration: had the 1669 eruption (which originated at about 800 m elevation near Nicolosi) lasted only one month, its lava flows wouldn't have reached Catania. Instead, it lasted four months and lava flows repeatedly invaded the town (although Catania was NOT, as is generally thought, completely destroyed - this work was accomplished 24 years later by a devastating earthquake of tectonic origin). 2. Can the next flank eruption be forecast or predicted? Top In the long term, all that can be said is what has been said in the answer to the previous question. In the short term, an identification of an imminent eruption and its location will very likely be possible, based mostly on premonitory seismicity and ground deformation. An intrusion of magma into the flank of Etna will be detected by the seismic and geodetic network. In fact, all flank eruptions since 1981 have been preceded by up to four days of intense seismicity that could be identified as probable precursor. In the case of the 1981 eruption, volcanologists of the Istituto Internazionale di Vulcanologia (IIV) were actually flying in a helicopter over the northern flank of Etna in the moment when the first eruptive fissures began to split open - right where the premonitory seismicity had occurred. The July-August 2001 eruption was preceded by four days of vigorous seismicity, ground fracturing and rapid inflation (uplift of the ground in specific areas), so that there was little doubt that an eruption was imminent. Yet there is no means to predict the duration and volume of an imminent eruption (this is impossible even after the eruption has actually begun); this was the case in July 2001 when almost all observers were convinced that the eruption would continue for many weeks or months, but as a matter of fact, the eruption ended after only 24 days and produced no more than 25 million cubic meters of lava, a mere tenth of the lava volume produced by the much larger and longer 1991-1993 eruption. Another major problem volcanologists have to deal with (not only in the case of Etna) is that a volcano may show signis of unrest without producing an eruption thereafter. At Etna, in 1989 and late 1997-early 1998 there were clear indicators that magma was intruding to shallow depths under the flanks of the volcano, but in both cases no eruption occurred in the areas of the anticipated outbursts (southeastern flank in 1989, contemporaneously with an eruption on the northeastern flank; western flank in December 1997 and January 1998). However, the next eruption after the 1989 intrusive event (1991-1993) was accompanied by the formation of fractures adjacent to the 1989 fracture system. 3. Can lava flows at Etna be diverted? Top The answer is: under certain favorable circumstances (high elevation of the eruptive vents, low mass eruption rate, enough time to carry out the necessary preparations) a diversion of lava flows is possible. There are various limits to this possibility, which will be evident in the following discussion of the historically documented attempts to divert lava flows at Etna. Interventions to change the course of lava flows coming from flank eruptions on Etna have a certain tradition. It was here that the first historically documented attempt of a lava flow diversion away from threatened areas was undertaken, during the 1669 eruption whose lava flow was menacingly advancing towards Catania. A group of men from Catania ruptured the walls of a channel along which the supplied lava to its front near the town in order to force it out of its bed which served as a protection from heat loss. From descriptions of this manoeuvre in historical sources it is apparent that it was crowned by some success - at least from a technical point of view, but the effect of the successful diversion of the lava flow was that now it threatened another town (Paternò), whose inhabitants prevented the Catania team from maintaining the breach in the lava channel wall open. As a result, the breach closed, and lava continued to advance towards Catania where it caused significant damage. Less known measures to prevent the spread of lava flows within the city of Catania during the same eruption include the construction of barriers across the main roads leading to the center of the city which actually halted the advance of the lava and saved the center of the town from destruction. The principal attempt of lava diversion in 1669 led to the creation of a particular legislation which prevented the diversion of lava flows at Etna, a law that was valid until 1983. In May of that year, a lava flow from a south flank fissure at about 2300 m elevation advanced slowly in the direction of the towns of Belpasso and Nicolosi (although it was still several km from both), having already consumed parts of the ski lifts, several restaurants and other tourist facilities, isolated houses (many of them constructed illegally), arable land, forests and various sections of the road from Nicolosi to the Rifugio Sapienza area (at about 1900 m elevation). It has been a matter of controversy whether there was any real threat to the towns, but in any case it was decided that the lava flow be diverted by means of blasting the walls of its main feeding channel with explosives. This operation was carried out on 14 May 1983 and was described as a partial success; technical problems during the preparation of the intervention prevented the complete destruction of the lava channel wall, and only a small fraction of the flow was diverted for short time into an artificial bed. It was during the same (1983) eruption that another kind of measure was used to protect several major buildings which were immediately threatened by the lava flow (Rifugio Sapienza, the Astronomical Observatory and the Grand'Albergo dell'Etna), this consisted in the construction of earthen barriers parallel to the flow margins. It was thus aimed to prevent the lateral spreading of the lava field towards those structures, and in fact none of them were destroyed. Nine years later, a lava flow from a fissure high on the southwestern wall
of the Valle del Bove gradually advanced towards the town of Zafferana on the
southeastern flank, and a new series of protective measures were introduced
to halt the lava flow or at least slow its speed. The first such measure was
the erection of a large earthen barrier at the end of Val Calanna, a southern
outlier of the Valle del Bove, perpendicular to the flow direction. As expressed
explicitly by Barberi et al. (1993), this barrier was not intended to stop the
advance of the lava flow but to temporary slow it, in order to let some time
pass during which other protective measures could be taken or the eruption could
end. The basin behind the barrier was gradually filled by overlapping lava flows,
and then the lava eventually began to spill over the crest of the barrier and
down into the narrow valley leading down to Zafferana. A series of hastily erected
minor barriers at lower elevations in the valley (again perpendicular to the
flow direction) were rapidly overwhelmed by the advancing lava which destroyed
orchards and a few small buildings. Although the 1992 operation appears to have been a success from a technical point of view, it has been a matter of debate whether the threat for Zafferana was as great as indicated by supporters of the intervention, and whether the lava tube would have been re-established had not the mass eruption rate diminished right at the time of the successful blasting operation. In any case, the final 1992 blasting operation is regarded a success, with some consequences to the attitude of the people living near the volcano. In interviews made during the late 1990s with people from the Zafferana and Nicolosi area, when asked about their fear of a future eruption, many of them expressed that they had no fear because "when there will be a lava flow it will be diverted anyway". However, the prospects were not all that simple at that time, and the July-August 2001 eruption was to teach a few interesting lessons. During the July-August 2001 eruption on the southern flank, three (out of a total of seven) eruptive fissures delivered lava flows that caused damage and threatened to cause much more extensive destruction, especially in the area of the Rifugio Sapienza and the Etna cable car, where there are numerous tourist facilities (hotels, restaurants, souvenir shops). In order to limit destruction to a minimum, earth barriers were erected and channels were excavated, which were hoped to prevent the menacing lava flows from extending laterally. Two major lava surges, on 26 and 30-31 July, rapidly spilled down the steep slope above the threatened structures and were largely confined by the barriers and artificial channels, with minor overspills occurring in a few locations. One of these came to within less than 50 m of the departure station of the cable car, another nearly reached a building of the Provincial Tourism Agency, but both were relatively small and short-lived, and the latter was cooled by spraying water onto its front. In eruptions like those of 1983 and 1991-1993 which were characterized by low effusion rates and whose eruptive vents lay at higher elevations than 2000 m, there is a good chance that the lava will take quite a while before reaching inhabited areas - if at all, since at low effusion rates the lava tends to form overlapping and adjacent flows of approximately the same length instead of forming a single long flow which simply extends further and further downslope. A diversion is possible where there are pathways for an artificial flow not occupied by areas and structures of value. If, on the other hand, an eruption were to occur in the densely populated area on the lower southeastern flank of Etna, even at low effusion rates the problem would be one of lacking space where a lava flow could be diverted. The problem would be much more evident in the case of a high-effusion rate eruption, even when the eruptive vents are located relatively high on the mountain. The March 1981 eruption serves as a dramatic example: in this event, a system of eruptive fissures rapidly propagated down the north-northwestern flank, feeding voluminous lava flows that advanced frighteningly swiftly towards the area of Randazzo and the small village of Montelaguardia lying to its east. Fortunately, the main phase of the eruption lasted less than two days, and the main lava flow narrowly missed Randazzo and Montelaguardua, passing right midway between these towns. However, during its advance the flow overwhelmed numerous isolated buildings and interrupted two main roads, two railway lines, and power supply to Randazzo. In the case of the 1981 eruption, there would have been no chance of a lava diversion. The necessary conclusion is that although some possibilites to control and influence the advance of a lava flow do exist, they are limited to eruptions from vents at high elevations which are characterized by low effusion rates, in sectors of the volcano where there is space to accomodate an artificial lava flow produced by diversion without the production of significant damage. 4.How many people have been killed by eruptions of Etna? Top This is one of the questions to be answered most easily. Etna is definitely NOT a killer volcano. Very few people have been killed by eruptions of Etna: a detailed study of all original sources described in "Etna and Man" has revealed that in recorded history (which goes back to about 1500 B.C.) there have been 77 confirmed deaths that can be directly attributed to eruptions of Etna. This low number is mostly due to the fact that Etna's eruptions are rarely violently explosive, and lava flows move slowly allowing people to leave long before the lava front arrives at their homes. Virtually all cases of human fatalities at Etna are due to the fact that humans were in areas where they should not have been in that moment, like the nine tourists who were killed in September 1979 near Bocca Nuova by a vent-clearing phreatic explosion. That event had been preceded by similar phreatic explosions during the days before and was characteristic of the volcano's summit crater behavior in a period after a flank eruption. A strikingly similar incident (with two deaths) occurred in April 1987 at the SE Crater, and another is known to have occurred at the NE Crater on 2 August 1929 when two people were killed by a phreatic (?) explosion. The most serious incident occurred during an eruption on the W flank in 1843 when 60 forest workers killed in 1843 near Bronte in a phreatic explosion caused when a lava flow moved over a water reservoir, causing instantaneous evaporation and explosive expansion. Fatalities are also reported in various sources (all of which are secondary) in the case of the 1928 eruption which destroyed the town of Mascali; these sources report up to five people killed, including an elderly couple caught asleep when a lava flow invaded and destroyed their home. However, a thorough literature research and interviews with eyewitnesses of the eruption by Duncan et al. (1996) revealed that there were no deaths during that eruption and the reports about fatalities were evidently derived from rumours picked up by the foreign press (A.M. Duncan, personal communication; Duncan et al. 1996). Mascali was orderly evacuated prior to destruction and its residents found accomodation mainly at their relatives' homes. The 1928 eruption was similar to the 1981 eruption on the NW flank in being characterized by high effusion rates and in occurring outside the areas of frequent flank eruptions, but nonetheless the advancing lava flows left enough time not only for evacuation, but many people salvaged furniture and removed even the rooftiles of their doomes houses. Widely distributed literature attributes many deaths (up to 20,000 in some sources) to the 1669 eruption whose lava flow destroyed parts of Catania. This information also popped up again in newspapers during the summer 2001 eruption. Such reports are usually vastly exaggerated even where describing the magnitude of destruction in Catania which was by no means completely buried by the lava flow (Pagnano 1992). It is evident that there is some confusion with the devastating earthquake that struck the city only 24 years after the eruption; this event did indeed transform the city into a heap of debris, killing two-thirds of its inhabitants, and causing death and destruction all over southeastern Sicily. The 1669 eruption is not known to have killed anybody, neither in Catania nor elsewhere. The lava flow that issued from craters near the town of Nicolosi on the S flank arrived at Catania only one month after the beginning of the eruption. Can anybody imagine those poor residents of Catania waiting a full month to be buried by a lava flow? What has been said before is in striking contrast with the number of people killed on Etna in other circumstances during recent years. Since 1980, two people were killed by eruptive activity, but since 1995 alone, at least 5 people were killed by lightning or by other causes. This trend seems to be rising, and the more people will die or get injured on the volcano, the more severe will be the access restrictions. 5.Is it safe to climb to Etna's summit? Top The answer is quite simple and drastic: NO, IT IS ABSOLUTELY NOT SAFE TO GO TO THE SUMMIT AREA OF ETNA. This is not only so when the summit craters are erupting. Etna is a surprisingly large mountain where people can easily lose orientation, and this huge mountain creates its own microclimate. Even when there are generally stable weather conditions in Sicily, Etna may be shrouded in dense clouds, and often these produce downpours and thunderstorms. Since 1999, three people were killed by lightning in the higher areas of Etna. Nonetheless, many feel attracted by the frequent summit activity and go, often alone, during unstable weather, and not well equipped for that kind of excursion. Apart from the risk these people face (of getting lost in bad weather and/or injured by the volcanic activity or by falling), there are some unpleasant insurance problems and a general bad taste such incidents leave to those involved. So, besides the official access restrictions which have to be handled with highest diplomacy, it is recommended to everybody who intends to visit Etna: NEVER go to the summit alone, NEVER go unless weather conditions are extremely stable, and NEVER go if there is a visible increase in the eruptive activity at one or more of the summit craters. If you really believe that you must go into the restricted area (which, I repeat, is very dangerous), don't do that before the eyes of the tourists who go with the mountain guides, and who are told that one may not go beyond a certain area, hundreds of meters below the summit craters. And please keep in mind the following: Etna is an active volcano. This means, there are projectiles flying out of the summit craters and staying in their range is very dangerous. People who are lacking experience risk to react in the wrong manner, thus increasing the probability to get hurt, even simply by falling in an area where running is not the best idea. Even when in a certain moment there is no visible eruptive activity, the risk of very sudden and violent vent-clearing explosions (such as those which killed nine people in 1979 and two in 1987) exists. In recent years the activity mainly consists of so-called paroxysmal eruptive episode, which occur at the SE Crater at irregular intervals. These events are unbelievably violent and many begin quite abruptly. There have been numerous occasions when the area surrounding the Torre del Filosofo mountain hut was showered with incandescent bombs up to 0.5 m across, and more than once people observing the activity from there had to run for their lives to find shelter from the surprising rain of such large projectiles. If there is cloud cover this will also prevent anyone from seeing what activity is going on and where fragments of lava are falling. Etna has a much more complex morphology than may appear when it is seen from some distance. It is very easy to COMPLETELY lose orientation rapidly once clouds have veiled the area you're in (this has occurred even to people who know the mountain very well), and there are areas where it's best to have very good visibility (like the near-vertical boundaries of Valle del Bove). So if you want to visit Etna, check the local weather forecasts (among which the satellite images have proved to be most reliable), contact the mountain guides (at the Rifugio Sapienza mountain hut and at the base station of the cable car or at the hotel "Le Betulle" at Piano Provenzana) and leave word that and where you are going, and when you intend to be back. If possible, bring a field compass with you - even though this might not indicate the true north because of the magnetization of the lava flows. Cell phones may be highly precious devices in emergency situations on Etna, but be aware that there are areas on the mountain where there is no signal. Do also carry suitable clothes (including serious hiking boots), torches (with a set of fresh batteries) and enough water and food (chocolate is very efficient once you run out of power). If you respect these rules, a visit to Etna's summit area (outside the restricted area) will not be more dangerous than riding the car in your home town. How to go to the summit area? If you love the intense contact with nature and
are an experienced mountaineer, you may feel free to climb Etna from wherever
you want - at your own risk. The only access route for less experienced climbers
to the higher portion of the mountain is presently on the northern side (Piano
Provenzana). From there one can walk up the dirt road that arrives near the
summit craters, and enjoy a wealth of breathtaking panoramic views. The walk
is long - about 10 km - and covers a vertical distance of about 1500 m. Before
you go, try to get as much information about the current state of activity and
the weather situation at the Hotel "Le Betulle", where excursions
on Etna are organized. 6.Is Etna a stratovolcano or a shield volcano? Top I have been asked this question or similar ones quite often by students who have to write papers on a selected volcano, and many have chosen Etna, only to find quite confusing information regarding the morphology of Etna. Among my answers were the following: "It is difficult to classify Etna in terms of morphology. Etna has the
morphological characteristics of both shield and strato volcano, and furthermore
it has various calderas, the largest being Valle del Bove on the eastern flank.
The lower part of the mountain in some areas is clearly a shield on top of which
a stratovolcano has built, but I would best describe it as a complex volcano.
To complicate the picture, Etna has some 250 cinder cones on its flanks some
of which would rank as volcanoes for themself in other areas. On Etna they are
merely lateral vents, products of Etna's flank eruptions. Maybe the most precise
answer to the question is: "Etna is a mixture of overlapping shield and
strato volcanoes partially destroyed by repeated caldera collapse and partially
buried by younger volcanic edifices"." "Etna unfortunately does not fit easily in these classification schemes.
In part it is a shield, in part a strato volcano, and then it is also a caldera
volcano because it actually consists of numerous volcanic edifices that grew
on top of each other, and each suffered major collapse at least once during
its lifetime. Etna is thus best described as a complex volcano... 7.To what kind of tectonic environment is Etna related? Top This is another of those questions that are not very easy to answer. Read here too. First, read an answer to a person who had asked about the general tectonic framework of Italian volcanism: "Volcanism in Italy is generally due to the collision of the African and the Eurasian plates. However, few volcanoes in Italy are alike. The volcanoes farther north, in Latium and Campania, among which there is Vesuvius, may be in some manner subduction-related, but this is not clear. The volcanoes of the Aeolian Islands, such as Stromboli, Lipari and Vulcano, are at least in part due to subduction of the oceanic (?) crust of the Ionian sea under the Calabrian Arc, but there are some characteristics to Aeolian volcanism that do not agree with that picture. Etna may really be the product of a hot spot, but it is also related to a complex tectonic situation, with numerous major faults intersecting at the volcano. There are finally the volcanoes south of Sicily (Pantelleria and Linosa) which are due to continental rifting, similar to the East African Rift." 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; see also "Tectonic setting and geological evolution". "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 Messina-Giardini fault zone; McGuire et al. 1997); (4) dilatational strain on the footwall of an east-facing 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." 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.
8.How fast do Etnean lavas move? Top Eruptions of Etna are often seen in television news services to emit broad streams of brightly incandescent, fluid lava which spill down its flanks to distances of many kilometers. Yet the lavas of this volcano are much more viscous than those of the Hawaiian volcanoes or of Piton de la Fournaise volcano on Réunion island in the Indian Ocean. The velocity at which lavas move depends on several factors, such as (1) the distance from the eruptive vent(s), (2) the effusion rate, (3) the steepness of the slope on which the lava is flowing, (4) the temperature of the lava, (5) the crystal content of the lava, (6) the presence (or absence) of lava flow channels and/or tubes. Near its source the lava generally flows at a speed of up to several meters per second but rapidly slows as it extends further. Flow within channels or tubes (which generally develop within days to weeks if supply of lava from the eruptive vents continues at a more or less regular rate) can be nearly as fast as at the source, even at a distance of hundreds of meters or even kilometers. The advance of a lava front, on the other hand, shows an exponential decrease in velocity with increasing distance from the source (or the outlet of a lava tube). At a distance of hundreds of meters or kilometers from the source, a lava front generally advances at a few meters or a few tens of meters per hour, which is slow enough to permit observations at close range and, if a lava flow is encroaching on buildings or population centers, to save human lives and often also property such as households and parts of the threatened buildings. For this reason lava flows at Etna almost never cause deaths and rarely cause injuries. When a lava flow approaches and consumes man-made structures, this process is often painfully slow, and owners of homes or cultivated terrains often stay until the very last moment to watch how the lava does its work of destruction, hoping that a miracle will stop the advance of the lava.
9.How do the people living near Etna feel about "their"
mountain? Top The relationship of the inhabitants of the Etna region with the volcano is a peculiar one. In the first place, it is characterized by a strong pride for the mountain, which they are fully conscious of being a kind of myth and of worldwide fame and fascination. It is no coincidence that the people living around the volcano call themselves "Etnei", which means "Etneans". Etna and its eruptions strongly condition their lives in both a positive and a negative sense - positive because the mountain is their home, and its volcanic nature is the reason for the extreme fertility of the area, the beauty of the landscape and the arrival of numerous tourists which provide a major source of income for the region; negative because eruptions at times disrupt the daily routine and may even destroy homes and land property. The Sicilians call Etna "a' muntagna", which simply means "the mountain". THE mountain. "A' muntagna" is female, and it is common to hear people talk of "la nostra signora" (our lady), which reveals feelings that are both a love affair and a mother-children relationship. In fact Etna is something like a big Sicilian "Mamma" that provides enormous quantities of very tasty food and a comfortable home, but every now and then the Mamma gets nervous and slaps her children in the face without letting them really understand why. In a kind of "appeasement" strategy, the "Etnei" insist on telling people that come from elsewhere that "la montagna è buona", she is a GOOD mountain, a good volcano. There is a strange difference between the people living in the villages higher on the slopes of Mount Etna and those living in the larger towns near the coast. While the earlier - especially the simple farmers - rarely look up to see what happens at the summit and NEVER EVER go there, the city people are quite curious, although very few of them ever go to the summit area. They prefer to have nicely illustrated books, videotapes and photographs at home and assist to public slide shows and video projections. Only when lava flows reach areas or can be seen from points that are easily accessible by car they begin to move in masses to "see the lava". The July-August 2001 eruption provoked an unprecedented assault on such areas, with people hiking many kilometers without being prepared in the least way to get as close to the advancing lava flow as possible. There are a few associations of naturalists, hikers and passionates of trekking in Catania and nearby towns, but these represent a very small fraction of the population. Knowledge of Etna and its dynamics is surprisingly limited among the people to whom the volcano is part of the everyday life. For this reason unfounded and at times grotesque rumors rapidly spread in times of significant eruptive events, as has been seen during the 2001 eruption. A common misconception is that when there are eruptions there will be no earthquakes, which is probably based on the fact that many flank eruptions are preceded by (relatively small but frequent) earthquakes which essentially end once an eruption has begun. The major tectonic earthquakes that occur in the eastern part of Sicily at intervals of a few centuries are actually not related to the eruptive activity of Etna. Other interesting but erroneous notions include the "Sangiuliano vent" in the historical center of the city of Catania. This is a low hill of which many "Catanesi" believe that it once was a flank crater of Etna, which would make it the most remote eruptive center of the volcano. Naturally the presence of an old vent in the center of the city would be reason for significant concern, although the Sicilians quite easily consider a volcano "extinct", as they do in the case of the "Sangiuliano vent". Actually there was never an eruptive center in the city of Catania. The nearest eruptive centers related to the Etnean volcanism lie in the Acicastello-Acitrezza area to the north of the city, and these were active only at the beginning of volcanic activity in the area, about half a million years ago. Somewhat younger eruptive centers at Motta Sant'Anastasia and Paternò to the NW of Catania are still very old (some 200,000 years) and unlikely to erupt in the future. Most striking, though, is the fact that the Sangiuliano hill in Catania not only has never been the site of eruptive activity, but it is actually one of the few places in the urban area that have NEVER been covered by lavas of Etna (Monaco and Tortorici, 1999; Monaco et al. 2000). The substratum consists of Pleistocene sands, deposited before volcanism began in the Etna area, and this has been recognized by past generations of "Catanesi" for a large church sitting on the Sangiuliano hill is named "San Nicolò l'arena" ("arena" means sand). The legend of the "Sangiuliano vent" possibly originates from the fact that a lobe of the destructuve 1669 lava flow arrived in the backyard of the San Nicolò l'arena church. The Sicilians enjoy worldwide fame of being a highly religious people. Images of processions are associated with many eruptions which threatened villages even in the late 20th century and as recently as in 2001. It is also widely known that the veil of the patron saint of Catania, Sant'Agata, is believed to have miraculously stopped lava flows that were menacingly advancing toward major population centers on various occasions. The veil was carried in processions to the active lava fronts, and as a result these stopped moving and disasters were thus prevented. Such cases are reported for the eruptions of A.D. 253, 1444 and 1886 and significantly contributed to the strong feeling of veneration of the "Catanesi" for their patron saint. Yet far more eruptions of Etna, including that of 1669, caused widespread destruction, and it is not known whether the veil of Sant'Agata was employed in efforts to halt the lava flows of these eruptions. The historical sources simply do not mention them. In any case it seems that there is a logical, not all-too-mystic explanation for the miracles of A.D. 253, 1444 and 1886. Throughout the past centuries clergymen were among the few people in Sicily that possessed a certain level of education and semi-scientific knowledge, and they certainly had precise concepts about how Etnean eruptions worked. It must have been of little difficulty to them to recognize when an eruption was showing signs of exhaustion, and those were the right moments to carry the sacred veil to the lava fronts, because it was more or less foreseeable that these would advance little further. Images and video footage of mass celebrations and processions were common during the July-August 2001 eruption on the S flank of Etna, and they had a certain touch of dramaticism with the erupting volcano behind the anxious expressions in the faces of the participants. While it is true that most Sicilians are catholic, religious practice in their everyday life is often routine and demonstrative rather than an expression of true conviction, since in many respects they do not strictly follow the rules of life and social and sexual behavior imposed by the Catholic Church. Participation in the processions of July 2001 was rather for "better safe than sorry" reasons, there was never anything like true fear during that eruption, and after fulfilling their religious duties many of the people joined a much larger, non-religious procession which continued from the first to the last day of the eruption, the procession of those who went to "see the lava". See "Etna and Man" for more information on the complex and fascinating coexistence of the "Etnei" and the volcano. References Monaco C and Tortorici L (coordinators, 1999) Carta geologica dell'area urbana di Catania (1:10,000). SELCA Firenze. Monaco C, Catalano S, De Guidi G, Gresta S, Langer H and Tortorici L (2000) The geological map of the urban area of Catania (Eastern Sicily): morphotectonic and seismotectonic implications. Memorie della Società Geologica Italiana 55: 425-438. 10. How do the people living near Etna feel about "their" mountain? Top The following is a question (from a student in Israel) regarding this subject, and my answer (with a few additions) to this question. More detailed explanation is given below. Q: "Is there any connection between the occurrence of earthquakes and the activity of Etna?" A: "Yes, sometimes. There are tectonic earthquakes (...) which occur on faults, similar to the San Andreas in California and, I think, some faults that you have in your country and nearby. These are the strongest earthquakes which can be devastating (most recently in 1693 when Catania was totally destroyed). They are not related to the volcanic activity. Volcanic earthquakes, due to movements of magma below the surface, occur frequently on Etna..." Sicily is a seismically very active region. Earthquakes are frequent along two major fault systems that extend from Etna to northeast (Messina-Giardini or Messina-Etna fault system) and southeast (Malta Escarpment fault system), and the most devastating earthquakes of the past centuries had their epicenters there. Such earthquakes may exceed a magnitude of 7 (as in the cases of 1169, 1693 and 1908) and are extremely destructive due to the widespread lack of earthquake-proof constructions. The epicenters of these events lie at a distance of about 80 km from Etna in both directions, too far to be directly connected to the activity of the volcano. There are also many smaller (though at times destructive) earthquakes that originate at faults cutting the eastern, northeastern and southeastern sectors of Etna. These are known as "Etnean earthquakes", but until now no evidence has been found for a direct correlation with the eruptive activity. They are rather envisaged to be the result of movements in a sector of the volcano that is considered "mobile", which is confined between the Pernicana fault on the NE side and the Mascalucia or the Ragalna fault on the S side of Etna. These faults are what geologists call "strike-slip faults" because movement along them is essentially horizontal. Many normal faults that crisscross the "mobile" E sector of Etna are seismically active and thus produce frequent earthquakes; since the hypocenters (the zones at depth where earthquakes originate) are close to the surface, they can be locally devastating although they are never as powerful as the earthquakes along the large fault systems of eastern Sicily. The faults themselves form a spectacular "step"-shaped morphology that gives the E flank of Etna its peculiar character; these steep fault scarps are called by the local people "timpe" (sing. "timpa"). While seismic activity at the "timpe" does not appear to be correlated with visible eruptive processes on the volcano, it is likely that it is to some degree influenced by magma movements deep within the volcanic edifice. Then there are truly volcanic earthquakes which are caused by the uprise of magma through fissures in the flanks of the volcano. These occurred in spectacular quantities during the days before the July-August 2001 eruption and were one of the clearest indicators of the imminent eruption. Volcanic earthquakes are generally too small to provoke significant damage (the destruction of Nicolosi by pre-eruption seismicity in 1669 is among the few exceptions, but this was due to the location of hypocenters at shallow depth immediately below the village), but they are often felt by nearby residents. 11.When was Catania last affected by an eruption of Etna? Top If "affected" is understood in a broader sense, such as ash falls, then Catania is very frequently affected by eruptions of Etna. Between 1995 and 2001 ash fell on more than a dozen occasions in the city and beyond, and light ash falls again occurred in late March 2002. If "affected" means that the city was threatened or invaded by lava flows, then the answer is: in 1669. That eruption occurred from a crater at only about 850 m elevation, near the town of Nicolosi, and produced a voluminous lava flow which (after destroying fifteen smaller villages) arrived at the city walls of Catania one month after the beginning of the eruption. Initially the city walls deflected the flow around the southern part of the city into the Ionian Sea, but the failure of small portions of the walls eventually permitted lava to invade the city. Fortunately the lava lobes that entered the city were small and poorly fed, so that they destroyed relatively small parts of it; furthermore it was possible to stop the advance of these lobes by constructing barriers (made of the debris of buildings damaged by the lava) across the main access roads to the center of Catania. It must be noted in this context that the 1669 eruption is often described in geology text books, touristic guides and newspapers as having caused the total destruction of Catania and the death of up to 20,000 of its inhabitants. This information is completely false. The main lava flow produced by the 1669 eruption did cause some damage in Catania but this was limited to the marginal western and southern parts of the city, and about 80% of the buildings were not harmed. None of the contemporaneous descriptions of the 1669 eruption mentions any fatalities, which they would have certainly done had there been people killed by the eruption. The total destruction of Catania (and many other towns in southeastern Sicily) and the death of about 16,000 people - two-thirds of its inhabitants at that time - was accomplished by a devastating magnitude 7 earthquake which was of tectonic origin and was not related to the eruptive activity of Etna. Since 1669 there has been no eruption that even remotely threatened Catania; the nearest lava flow in this period came to within about 15 km of the city. However, geological mapping of the urban area of Catania in the late 1990s has revealed that the area now occupied by the city was almost completely covered by lava flows on six occasions during the past 5000 years: about 4500 B.C., in 693 B.C., in 425 B.C., in A.D. 252 (or 253), in the 12th century (this lava flow is often attributed to an eruption in 1381, but was emplaced about 200 years earlier), and in 1669. The most voluminous of these flows is that of 4500 B.C. and occupies much of the central portion of the city area, while the 12th century and 1669 flows essentially remained outside the city as it was in those days. Any future lava flow of similar dimensions would certainly cause extensive damage at least in the outskirts of Catania, but it is possible that the vast quantity of large buildings in those areas would provide a considerable obstacle to a lava flow and prevent it from invading the center of the city. 12. Is there a risk that Etna might blow its top, like Mount St. Helens? Top The following is a question (from a student in the USA) regarding the types of activity observed at Etna, followed by my answer (with a few additions) to this question. Q: Please tell me what type of eruptions Mt. Etna gives, Plinian? And explain what Plinian means, if Plinian is actually the type of eruption that Mt. Etna gives? A: Etna's typical activity is anything else but Plinian, Plinian is the most violent type of explosive eruption and occurs, every now and then, at Vesuvius. Tthe term Plinian is derived from the Roman name Plinius (in English this has become Pliny), and this was the name of an officer of the ancient Roman empire as well as of his nephew (the former being called Pliny the Elder, the latter Pliny the Younger). Pliny the Younger is the person who left to the world the famous account of the catastrophic eruption of Vesuvius in 79 A.D. which, in fact, was violently explosive, and it is after this eyewitness report that this type of eruption is called "Plinian", because it has been so well described by Plinius! Etna does produce such eruptions very rarely, and there has been none since more than 2000 years. The activity that we commonly observe at Etna is called "Strombolian". The term is obviously derived from Stromboli where the activity consists of discrete, separate bursts of incandescent fragmental material, that is, a mild explosive type of eruption. When Etna is in a period of "persistent" - long-lasting, virtually uninterrupted - activity, like it is since 1995, this Strombolian activity occurs at the summit craters, and this has been most characteristic at the Southeast Crater between late 1996 and July 1998. Another characteristic of Etna's activity in such periods is that there is lava outflow, which is not Strombolian (the volcano Stromboli produces lava flows only very rarely, most recently in 1985-86, 1993, and - very minor - in 1994). Then there are the more vigorous eruptions like those we saw at the Southeast Crater between September 1998 and February 1999, these were no longer Strombolian because the incandescent ejections blended into a continuous jet, and thus became similar to Hawaiian style lava fountains. Eruptions like that of 22 July last year, when an eruption column rose 10 km high, are typically called "Vulcanian", but as may have been understood from my answers to other questions, at Etna it is very difficult to apply strict classification schemes because many types of eruption appear, often near simultaneously. The following question was sent to me from the Netherlands and focuses on the destructive potential of Etna, it is followed by my answer. Q: How destructive can the Etna be? I mean, is it possible that the Etna can come to an enormous eruption with pyroclastic storms (like Mount St. Helens, U.S.A. 1980)? A: Explosive eruptions on Etna are rare and ususally limited to the summit area. However, at very long intervals, the volcano produces some more violent explosive eruptions, there was a large ignimbrite eruption some 15,000 to 18,000 years ago, and other major explosions occurred about 5000 years ago, and most recently in the year 122 before Christ when most roofs of Catania collapsed under the weight of tephra. To change its eruptive behavior from the normal mild Strombolian and largely effusive activity to highly explosive, something drastic must happen in the conduit system, that is, in the pathways that lead from the Upper Mantle to the craters, like a long-lived blockage that allows the magma to change chemically (differentiate, as it is called in geology) and thus become more likely to erupt explosively. This is currently not occurring, since magma rises freely and near continuously to the summit. The third question, probably from a person in Malta, is similar, but it is reproduced here with my relative answer for completeness, and because I always find other ways to respond to similar questions... :-) Q: What are the possibilites of a full blown eruption happening? A: Etna does not produce very explosive eruptions, such as Mount St Helens or Pinatubo. The worst that can happen is that lava flows from a fissure very low on the flank of Etna and reaches the densely populated areas around Catania, but lava usually moves very slowly and people have time not only to save themselves, but also to carry away most of their things from their homes if necessary. The risk of such an eruption (the most recent of that kind occurred in 1669) is very low but nonetheless there is a possibility. For the moment, however, there are no indications that such an event can take place in the near future. 13. Are my relatives living near Etna in danger? Top Many people, mostly Americans, are concerned about their relatives (personnel of the military base at Sigonella, some 15 km south of Catania) who live near Etna, after receiving news about Etna via television news and newspapers that are often exaggerated or contain false information. This was particularly the case during the July-August 2001 eruption, and as a result many people cancelled their holidays in Sicily. There is absolutely no danger to the lives and health of anyone living near
Etna, even in the case of a major explosive summit eruption. The worst effects
in that case would be falls of tephra (that is, dust to sand-sized particles
called "ash", and small fragments of highly porous scoriae) that can
disrupt traffic, and leave a dirty cover on roads, buildings, and any other
free surface. In recent decades, the most distant places affected by tephra
falls were the town of Siracusa, some 80 km south of Etna, in August 1979, the
southernmost of the Aeolian Islands, some 100 km north of Etna, in January 1990,
and the northern coast of Africa, in July 2001. Catania received its most recent
significant tephra falls during the July-August 2001 eruption. During these
and various previous eruptions, the airport of Catania had to be closed because
of the ash falls. In the case of a major eruption of Etna, do not trust too much the information spread by the mass media. Contact your relatives directly, or check this site to see the Etna News Page which will give you frequent updates during an eruption of Etna. 14.Is being a volcanologist a dangerous job? Top Is it? Goooood question. You may have read Stan Williams' book "Surviving Galeras" and/or its counter-book "No apparent danger" by Victoria Bruce, and think "Gee one has to be crazy to be a volcanologist". I personally think that it is wrong to simply say doing the volcanologist is a dangerous job. It CAN be dangerous, but there are also many ways to prevent this and work tranquilly on active volcanoes without exposing oneself to great danger. Me and my colleagues who study Etna feel like doing a job just as someone working in an office, and much of our work is indeed done in the office, in front of a computer, or in a laboratory. Work on Etna, especially when it is erupting, of course is nothing like that. It is exciting, at times frustrating, and if one gets close to an erupting crater there is a certain risk. But Etna rarely takes us by surprise. We believe to know this volcano well enough to understand when a situation is too dangerous and when it is not. This does not exclude that someone of us might be wrong and caught in a sudden explosion, but my personal experience is that any volcanologist ending up in a rain of bombs or scoriae has been perfectly aware of this possibility and nonetheless chosen to enter into an area at risk. Yet so far no volcanologist has ever been killed on Etna (and surprisingly few non-volcanologists have been killed by this volcano), and none of my colleagues (myself included) seems to be willing to be the first to obtain this pitiful fame. Most volcanologists are not the heroes that you may have seen in newspapers and in television who put on weird-looking asbestos suits and clamber across moving lava flows near explosively erupting vents to pick lava samples. Most of us never think something like "it is on an erupting volcano that I feel best" although being close to one of them is certainly an extraordinarily thrilling and elating experience. I must admit that I feel extremely good as well at home with my wife or going out with friends or taking a long walk alone in the vast forested areas on the flanks of Etna. I do not search the thrill of danger and am not likely to render the photogenic impression of a cool-hearted "volcano chaser" who knows nothing better than to scramble across endless lava fields (preferably if they are hot or still moving) or to enjoy a refreshing shower of volcanic projectiles. If I need lava samples I find them in equal quality in a more distal position of a lava flow, remote from falling ejecta. Each time a hail of lapilli (or in the worst cases, bombs) falls around me I swear that this will be the last time that I expose myself to such a danger; this is among the least pleasant experiences that I can tell of. At least I am sure to wear a hard hat in any occasion when a repetition of this experience is even a remote possibility. Fortunately there have been few of these close encounters with the coarse-grained fallout of volcanic activity. Believe it or not, but it is an even less pleasant experience to have finished a day of work on Etna and nearly end up in a car accident while returning home. I swear that it is never me to provoke these quasi-crashes since I do not drive (don't ask me for the reasons, but there are a few). Other car drivers to me are much less predictable and thus much more dangerous than Etna. And if we really feel the need to reason about dangers, it is not volcanoes that are dangerous. LIFE is dangerous. It is full of traps of all kinds, so if we feel like pondering on the dangers from volcanoes, it is appropriate to ponder about all the other dangers as well. In that case we would soon be in urgent need of an extended session at a psychiatrist's. Better enjoy life as long as this is possible, and better enjoy volcanoes and the fascinating search to unravel their secrets. I am far too curious to see what Etna will do in the future to risk my life at such an early stage. |
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Fiore - VulcanoEtna - Web development Andrea Fiore
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