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Mt. Vesuvius is the best known volcano on earth; it dominates the Bay of Naples with its characteristic cone. It is a typical example of a volcano in a volcano made by an outer broken cone, Mt. Somma (1133 metres) with a crateric belt most of which is destroyed. In it there is a smaller cone, the Mt. Vesuvius (1281 metres), divided by lowering named Valle del Gigante (Giants Valley), a part of the ancient caldron where in a later period, perhaps during the 79 A.D. eruption, the Gran Cono (Great Cone) or Mt. Vesuvius arose. The Valle del Gigante is still divided in Atrio del Cavallo on the west and the Valle dell'Inferno on the east. The Somma's ancient crater is well preserved as far as its entire northern part is concerned, in fact in historic times it was less exposed to the volcano's devastating violence, because it was well protected by the height of the internal face that has prevented the downflow of lava on its slopes. The slopes, which vary in their steepness, are furrowed by profound radial grooves produced by the erosion of the meteoric waters. The whole section is then characterized by dikes and fringes of dark volcanic rock. The old crater edge is a stream of summits called cognoli. While the height of mount Somma and its profile have remained the same for centuries, the height and the profile of the mount Vesuvius have suffered considerable variation, because of the following eruptions, with raisings and lowerings. Mt. Vesuvius is a characteristic polygenic mixed volcano, meaning that it is constituted by lava of different chemical composition (for example trachytes, tephrites, leucitites) and formed either by casting of lava or pyroclastic deposits. All the zones at the slopes of the mountain are formed by transported earth of lava mud which goes down from the steep slopes in the rainy seasons through deep and narrow grooves called channels or more commonly "lagni". The high embankments are formed by piles of lavic scoriae, which precipitated in incandescent state and spread towards the low slopes, proving precious for the vegetation thanks to their fertile material, rich in silicon and potassium. Proceeding along the rim of the crater, one can observe the whole extent of the southern part of the volcano and, during days with good visibility, it is possible to see the entire gulf of Naples, from the Sorrento peninsula to Cape Miseno, Procida and Ischia. It is also possible to note the large number of buildings which have been built on the vulnerable flanks of the mountain.
The eruption of the 79 A.D.
The eruption began on 24 August of the 79 A.D. towards noon. The first eruptive phase was characterized from strong "freatomagmatiche" outbreaks. After this phase, magmatic outbreaks were followed until the morning of the following day, feeding a column constituted mostly from gas, pomici and ashes that were raised until 30 kilometers. The high part of the column expanded, assuming the shape of a pine, and was pushed from the twenty towards south-east. The contained particles in it often fell to the ground, forming a layer of pomici that to Pompei and Oplonti caught up 2-3 m. of thickness. Partial collapses of the eruptive column generated piroclastic flows that noticed to high long speed the flanks of the volcano, caught up and destroyed Ercolano. The city of Pompei, the much farthest one, did not come caught up and the greater part of its inhabitants survived. During the last hours of the night the intensity of the eruptive activity diminished.
At the first hours in the 25 morning, a "freatomagmatica" outbreak generated piroclastici, turbulent flows - terrible "the base-surge " - that, travelling at the speed of a hurricane, came down along the slopes of the volcano, devastated the surrounding areas until distances of 15 kilometers and caused numerous victims also between the inhabitants of Pompei that were survivors to the first phase of the eruption. In the course of the day the outbreaks diminished of intensity and, in evening stopped of all, leaving one large pall of ashes and pomici on the huge area. The abundant rains, provoked also from the breaking in in the atmosphere of enormous fine particle and vapor amounts, mobilized this material, forming dense mud taps that came down from the flanks of the volcano and of the Appennine relieves along it goes them to them, ulteriorly having the territory of the vesuvian area.
The eruption of 1631
The eruption of 1631 has been most violent and destructive of the history of the Vesuvio in the last millenium. After along period of quiescence, approximately 5 centuries, preceded from one series of premonitory phenomena, which earthquakes and raisings of the ground, the volcano waked causing the death of approximately 6.000 persons and the devastation of an area nearly 500 km. 2
The eruption began at the 7 in the morning of 16 December, with the formation of an eruptive column of approximately 15 km., from which they began to fall pomici and ashes in the area to east of the Vesuvio. At the 10 in the morning of 17 December, from the central crater generated piroclastici flows, gas clouds loaded with magma fragments that, sliding to long high velocity the flanks western and southern of the volcano, they destroyed all that they met in their way. In the night between the 16 and the 17, and in the afternoon of the 17, the abundant rains mobilized the incoherent ash cover causing the formation of mud taps. The taps came down from the flanks of the volcano, from the slopes of the Appennine to north and the northeast.
The phase of paroxysm in the eruption lasted three days, provoking an enormous panic between the population. There were on the roads of Naples public confessions of sins, accompanied from extraordinary manifestations of penance, and were organized processions with the statue and the blood of S. Gennaro, so that the patron appease that divine temper of which the outbreak of the Vesuvio it seemed the indubitabile sign.
The Count of Monterrey, viceroy of Naples from January of that year, sent some ships to collect the survivors of Torre del Greco and Torre Annunziata. After some months, deeply upsetting from the event, it made to affix in Portici a tablet that it exhorts the descendants not to forget the nature about the mountain, and to recognize ready the premonitory ones of a volcanic eruption.
The eruption of 1944
On 18 March of 1944, during the occupation of the allied troops, began the last eruption of the Vesuvio, that concluded a period of activity begun in 1914, during which it had been taken place the only modest eruptions from the central crater .
Between 1914 and 1944, lave and the slag produced from the volcano had filled up crater, wide 720 m. and deep 600 m., than it had been formed during the previous eruption of 1906.
A little cone of slag it emerged from the crater.
The little cone of slag it begins to collapse and the sismic activity becomes more intense. A new slag cone born and collapsed again.
The eruption begins in the afternoon with slag launch. At the 16,30 a lavic strained overflowed from the northern part of the crater and catches up the Valle dell'Inferno at the 22.30. Nearly at the same time an other tap overflows from the southern part of the crater. At the 23 there was also a spillage of washes from the western part of the crater: the tap follows the railroad of the funicular and interrupts the railroad.
At the 11 the washes flows along the Fosso della Vetrana.
Between the afternoon and the night, new strained overflowed from the northern part of the crater. All the effusive activities are accompanied by sismic tremor with increasing amplitude until half of the day.
The southern tap arrests at a quota approximately 300 m. on the sea level. In the night, the northern tap catches up S. Sebastiano and Massa di Somma and is divided in two coppers that are left over in direction of Cercola, from which in evening they are distant approximately 1,5 km. S. Sebastiano and Massa di Somma come evacuate and the 10,000 inhabitants transferred to Portici. Around the 17, the spectacular fountains of wash begin to form, the last of which hard approximately 5 hours and catch up a height nearly 1,000 m. Fragments of wash and ashes moved from the winds in quota, are deposited on the Southeastern areas of the volcano, between Angri and Pagani. The smaller fragments catch up distances than beyond 200 km. towards south-east. Slag until a kilogram of weight catch up the city of Poggiomarino, at approximately 11 km. from the crater. Great still warm slag amounts are accumulated on the flanks of the Great Cone. The sismic tremor continues, with maximums of amplitude in coincidence with the emission of the fountains of wash.
Towards the 1 p.m. the eruption was in its maximum activity. A column of gas and ash rises at a 6 Km. of height. Ashes and slag fall on the south-eastern slope of the volcano. A big seismic tremor accompanies all the phase, during which the crater becomes wide.
A series of explosions are caused by the entrance of water in the volcanic duct and there was a swarm of earthquakes.
The eruption end. It caused the death of some persons, the collapse of the roofs and serious damages in S. Sebastiano and Massa di Somma.