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mercoledì 7 gennaio 2009

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Mount Etna Volcano built up of numerous more or less extensive volcanic edifices which have been superposed in time over an area of about 1.250 km, with its 3.345 m. height, represents the highest active volcano in Europe.

The ancient eruptive centres (168.000 - 100.000 years ago) were the first rather modest sub aerial volcanic edifices (Calanna, Trifoglietto I, Monte Po) of an essential effusive type. Subsequently, due to a change in tectonic conditions in the area, two impressive and prevalently explosive strata volcanoes were formed, Trifoglietto and Mongibello.

Trifoglietto (80.000 - 64.000 years ago) in the frame of which at least five secondary eruptive centres can be found (Serra Giannicola Piccola, Trifoglietto II, Zoccolaro Vavalaci and Belvedere), ceased to be active some time ago and is now almost totally demolished. In the area where it arose, the eastern flacks of Mt. Etna, a vast depression can now be found, called the Bove Valley.

From the studies of the volcanic products outcropping in its rocks and high (at times over 1.000 m.) walls, the evolution of the ancient Trifoglietto volcano can, in fact, be reconstructed.

These studies have evidenced that the Trifoglietto eruptive centres were all explosive in type (and therefore more dangerous than the present active volcano), and that during their activity they erupted enormous amounts of scoriae, lapilli and ash, which are now to be found in the form of tuffs, mainly on the eastern flank of Mt. Etna.

Mongibello (34.000 - 0 years ago) the products of which have been superposed on the north-western flank of the ancient Trifoglietto, is the present-day active volcano. Secondary eruptive centres have also been found on Mongibello, and in the course of its evolution two eruptive periods can be distinguished. The Mongibello antico (34.000 - 8.000 years ago) is characterized by explosive-type eruptive centres (Ellittico and Leone) similar to those of Trifoglietto, whereas Mongibello recente (8.000 - 0 years ago) is conversely characterized almost exclusively by effusive-type centres (Vulcano del Piano and the present-day volcano), from which vast amounts of lava have been emitted. At present, Mongibello recente is the highest and most extensive active volcano in Europe and, in the last twenty years, has been one of the most active in the world. Actually on Etna there are four active craters: the Central Crater that is divided in Voragine and Bocca Nuova, the North-Est Crater and the South-Est Crater.


the Bove Valley, situated on the eastern flank of Mt Etna, is a vast depression whose walls in some points exceed 1000 m. Its origin is very debated and complex: according to recent studies it is due to the coalescing of various caldera collapses that occurred during the evolution of Mt Etna volcano. The first of this collapses, that of the Calanna eruptive centre, took place ca 100.000 years B.P., while the last of any great importance was that of the Leone eruptive centre ca 8.000 years B.P. It seems that around 5.000 years ago there were other collapses in the central part of the western wall of the valley. In the 18TH century, the Bove Valley was a wooded zone belonging to the Archbishops of Catania, but from 1792 a series of great and small eruptions covered its bottom with a-a type lava flows. At present, it is an immense extensions of lavas with the remains of ancient eruptive centres protruding (Rocca Musarra, Monte Calanna). Numerous eruptions have occurred inside this valley, particularly along the western wall: 1792, 1802, 1811 (Monte Simone), 1819, 1838, 1842, 1852-53 (Monti Centenari), 1869, 1908, 1950-51, 1956, 1964, 1968, 1971, 1978, 1979, 1984, 1985, 1986-87 (Monte Rittmann), 1989, 1991-93; only the lava flows of 1852-53, 1950-51, 1979 managed to get past the limits of the valley and reach inhabited areas, while the lava flows of the others eruptions stopped inside the valley. For this reasons, the Bove Valley is considered an enormous, limitless natural reservoir able to receive all the lava produced by the almost continuous eruptive activity of Mongibello. On the walls of the valley, the lava flows and superposed pyroclastic material (ash, scoriae, bombs, ect.) tell of the evolution of the existent eruptive centres before the present-day active volcano Mongibello; one of this, Trifoglietto, at the end of its activity and after violent explosive events, collapsed leaving the present-day Piano del Trifoglietto. In addition, on the walls of the valley, numerous dikes outcrop (feeders laid bare by erosion), as witness of so many eruptions. The prevalent NNW-SSE, ENE-WSW and NE-SW trends of these dikes show the main up rise channels for the magmas in the volcano.


while recognizing that every eruption has characteristics of its own that distinguish it from any others, the Etnean eruptions can be divided, on the basis of their site and eruptive mechanism, into terminal, sub terminal, lateral and eccentric. The terminal eruptions, connected to the summit craters, are characterized by violent and often brief explosive activity (lava fountains, throwing up of bombs and incandescent scoriae), at times accompanied by generally not very consistent overflow of lava. Apart from the above-mentioned paroxysmal phenomena at the two pit-vents of the central crater (the Voragine Est or the Voragine and the Voragine Ovest or Bocca Nuova) and at the Northeast and Southeast craters, there is the continuous emission of more or less intense vapour and gas, at times together with more or less violent and impressive emission of ash and lapilli’s. The latter phenomenon is due to an almost continuous explosive activity at the bottom of the vents themselves (at depths varying from 100 to 400 m), or to collapses of the steep internal walls. Sub terminal eruptions are those in which the explosive activity occurs mostly at the summit craters, or at an explosive crater that was formed during the same eruption, while the effusive lavas are emitted quietly for a certain distance ( sometimes several kilometres). Lateral or flank eruptions are those in which, along an eruptive fissure, opening on the flanks of the volcano, owing to an intense explosive activity a single eruptive cone or a series of spatter and cinder cones (the so called “bottoniera”) are formed. At the base of these the effusion of lava takes place which causes numerous lava flows that, generally, run long distances (several kilometres) and covering vast areas of land. Eccentric eruptions finally are the ones when the magma up rise conduit is completely independent of the central crater feeder system, and the very infrequent eruption take place at low altitudes some distance from the summit area. Generally, isolated cones are formed, from the base of which more or less consistent lava streams are emitted. Studies of past and recent eruptions, carried out on all the reconstructible history eruptions, have also shown that two distinct types of eruption may generally occur on mount Etna: a) paroxysmal eruptions of short duration (days or weeks), characterized by abundant initial emission and by the fluidity of the lavas giving rise to long (7-15 km) and not very thick (up to 10 m) lava flows; b) quiet or slow eruptions characterized by constant, but not very abundant emission of lava lasting for long periods of time (months or years) and giving rise to lava flows spreading out in breadth (several km), rather than in length (up to 7 km), and generally being very thick ( more 15 m).

THE GREATEST HISTORICAL ERUPTIONS


in 1987, with a decree of the President of the Sicilian Region, the regional nature park of Etna was set up with an area of ca 50,000 ha. The communes included in it are all in the Province of Catania and are: Adrano, Belpasso, Biancavilla, Bronte, Castiglione di Sicilia, Giarre, Linguaglossa, Maletto, Maniace, Milo, Nicolosi, Pedara, Piedimonte Etneo, S. Alfio, S. Maria di Licodia, Ragalna, Randazzo, Trecastagni, Viagrande, Zafferana. The Nature Park is divided into four zones A – B – C – D, having different restrictive regulations.

ZONE A: Nature reserve zone, where the environment must remain intact. In this zone it is allowed, subject to very precise regulations, to graze animals, to cut trees, to carry out scientific research, to make excursions, to do downhill and crosscountry skiing, to pick mushrooms, access with motor vehicles is allowed only on the existent tracks.

ZONE B: Zone of general reserve, where agricultural, forestry and animal – safeguarding the natural and scenic environment.

ZONE C: Protected zone, where transformation of buildings and land is allowed only when it aims at improving the amenities of the Park (parking areas, touristic and cultural centers, picnic and games areas) and at maintaining the already existent touristic and sports facilities.

ZONE D: Controlled zone, where all activities are allowed under limited supervision.


The vegetation of Mt. Etna can be distinguished by different altitudinal belts characterized by different aspects of vegetation, basically due to climatic variations with altitude.


is mostly occupied by crops, prevalently citrus, above all at the lowest altitudes (ca 0-500 m a.s.l.). These crops have replaced the pastiche, olive and carob scrub-forest that once occupied the lower flanks of the volcano. The rest of the natural vegetation is limited to the edges of the crops an of the inhabited areas; of these, the Euphorbia (Euphorbia dendroides) is very significant. At higher altitudes (ca 600-1000 m a.s.l.), the vegetation was once characterized by holly oak (Quercus ilex), forests. Today, however, these have almost completely disappeared due to the anthropic impact. Crops are very widespread, above all vines, olives, almonds and pistache (on the western flank)and nut trees (on the north-eastern flank). The holly oak woods in some zones on the western flank are characterized by the presence of Oriental hackberry (Celtis tournefortil). Instead, on the eastern flank the woods are very fragmentary, and together with the holly oak, flowering ash (Fraxinus ornus) and European hop horn beam (Ostrya carpinifolia) can often be found. In some zones, between holly oak woods, the Spanish chestnut (Castanea sativa) can be seen.

is characterized by deciduous oak, above all by pubescent oak (Quercus pubescens). The above mentioned woods are not, however, uniformly distributed around the volcano and, moreover, they have largely been replaced by Spanish chestnut woods. In the zone of contrada Giarrita on the eastern flank, together with pubescent oak there is Adriatic oak (Quercus cerris). Above the pubescent oak and Spanish chestnut woods, there are those of Corsican pines (Pinus laricio) which in some places form splendid pine forests (pinete of Linguaglossa and Serra La Nave).

extends until the upper limit of the woods; in it there can be found European beech woods (Fagus sylvatica), very fragmentary and, in the more xeric zones, replaced by Corsican pine woods. In some zones, above all on the eastern flank, there are woods and scrub of Etnean birch (Betula aetnensis), a species considered by some Authors as exclusive to Etna. Another species very characteristic of the Etnean landscape is the Etnean wood waxen (Genista aetnensis), one of the most important colonizers of the lava flows.

extends above the tree limit where a characteristically low type of vegetation is found, formed of Sicilian milk vetch (Astragalus siculus), forming typical thorny pulvini. From 2.450 up to 3.000 m a.s.l, few plants only manage to survive, adapting to the difficult environmental conditions. They form a pioneer group characterized by the presence of Etnean-type French sorrel (Rumex scutatus fo. Aetnensis). Above 3.000 m up to the summit craters there is the volcanic desert, since the continuous eruptive activity of the volcano prevents any form of vegetable life.


on Etna zone: fox, wild cat, weasel, marten, dormouse, black-tailed dormouse, small shrew, porcupine, hedgehog, hare, wild rabbit, noctule.

on Etna zone: kestrel, buzzard, raven, chaffinch, crossbill, woodpecker, hoopoe, Greek partridge, Sicilian long-tailed titmouse, wheatear.

on Etna zone: viper, grass snake, collar snake, green lizard, Sicilian lizards, gecko, tortoise.

on Etna zone: Etnean cabbage white butterfly.

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