ACTIVITY 'OF VESUVIO
Over the last 25,000 years, volcanic activity is concentrated mainly in the plain bell to Vesuvius. The oldest products are pumice (pumice those of Codola) that are above the deposit of Campanian. This is probably the most violent eruption occurred 17,000 years ago, called the "pumice Sarno" or "basal pumice." Numerous other violent explosive eruptions have occurred since then.
Vesuvius entered the history of volcanology with the eruption of 79 AD After 1631, the volcano enters a state of persistent activity, with an almost uninterrupted succession of numerous effusive and explosive eruptions.
The eruptions of Vesuvius between 79 A.D. and 1631
(Drawn in part from a trip to Vesuvius, P. Gasparini and S. Musella, 1991, ed Liguori, Naples)
After the eruption of Mount Vesuvius in 79 falls a long silence and the first news of its ongoing activity ("emits a lot of ash that reaches the sea") is reported in 172 by Galen, a physician greek describing the properties of air dry site created by subterranean fires.
Dio Cassius tells of a violent eruption in 203, whose explosions are heard in Capua, 40 km from the volcano. News from other two major eruptions occurred in 472 and 512 are reported by Comite Marcellinus, Chancellor of the Emperor Justinian.
These reports that on November 6 472 "Vesuvius, Campania torrid upstream of the internal fires burning, vomited bowels burned; Portole darkness during the day with a small dust on the surface of all Europe."
The eruption of the 512 is fully described by Cassiodorus, a superintendent of King Theodoric, in a letter written to ask for exemption from taxes for the populations affected by the eruption. He reports that "flies (...) a burnt ash that, after forming pulvirolente of clouds, rain with drops of dust even on the overseas provinces (...). E 'can see rivers of ash flow like liquid flowing that draw warm sands (...) and the back of the field suddenly swell up to the treetops. "
Explosive eruption, which occurred between 680 and 685, is quoted by Paul Deacon in the Historia Longobardorum and others are reported in 787 and 968.
Leone Marsicano, in the chronicles of the Abbey of Montecassino, talking about the eruption of 968, refers to "a great and unusual fire that came down to the sea." In this eruption is perhaps the first evidence of a lava flow, defined as "resin sulphurous uninterrupted rushed impetuously towards the sea."
Several authors speak of eruptions in 991, 993 and 999, but since that time imbued with the conviction of an imminent end of the world, any reference to disasters must be viewed with some degree of suspicion.
In the chronicles of the Abbey of Montecassino is signaled another eruption lasted six days from 27 January 1037 and an explosive event between 1068 and 1078. The last eruption, the first of a long period of quiescence, with the beginning of June 1139 and is reported both by those who chronicles the Montecassino Abbey of Cava dei Tirreni, and secretary of Pope Innocent II, Falcone Benevantano, the who wrote that Vesuvius "threw for eight days powerful fire and flames".
There are no known reliable evidence on the activity of Vesuvius after 1139. Around 1360, Boccaccio writes that from Vesuvius, "now do not leave it 'flame will' smoke '.
In an unknown year of 1500, Ambrose Leo of Nola refers to an eruption lasted three days, which was followed by the formation of gaseous fumaroles. A Spanish soldier, climbed Mount Vesuvius in 1501 together with the Queen Isabella, described the crater as "a hole 25 to 30 inches of diameter and which is always going smoke" that according to some "the night becomes a vivid flame."
In 1575, Stephanus Pighius, a Belgian cleric traveling in Italy, describes Vesuvius "covered with vineyards, and so the hills and the surrounding fields." In the middle of its top opens a chasm, but the volcano "is cold, it 'seems to emit any heat or smoke."
From 1500 1631 is therefore certain that Vesuvius has been inactive or nearly so. The mountain was covered with crops destroyed and the country had started a new life, forgetting quickly past eruptions. Large trees grew up in Great Cone, the cone within the caldera of the Somma, and the whole apparatus was called the mountain of Somma, after the city that lies at the foot of Vesuvius.
In the night between 15 and 16 December 1631, including very strong explosions and earthquakes, Vesuvius back in business with an eruption that sowing panic and destruction. For several months the entire area was plagued by frequent earthquakes, which were intesificati few days before the eruption.
Giambattista Manso, a scholar of the time describes the eruptive cloud rising in part to the sky (Plinian column) and in part expands on the slopes of the mountain like a torrent (pyroclastic flows and surges).
The most violent phase lasted three days and throughout the eruption died out in five days, leaving a trail of mud flows and landslides of volcanic material accumulated on the slopes. Weak emissions of ash and earthquakes continued for months.
After this eruption Vesuvius has changed shape: the top, higher than the first sum, is decapitated and the crater, according to Bouchard, a French scholar went to the edge of the abyss, has a diameter of about two miles (three kilometers and half), compared to the previous mile. Towards the Greek Tower had opened six new eruptive vents.
The activities between 1631 and 1944
With the eruption of Vesuvius in 1631 entered a phase of persistent activity that lasts, except for brief periods, until 1944. It is therefore likely that, given the habit of seeing the active volcano, has lost the testimony of minor events and bring back only the chronicles of particularly violent eruptions.
Many of the eruptions were continued for over three centuries have evolved very similar: the initial activity is effusive with lava flowing from cracks or spilling over the edge of the cone. This phase can be accompanied by small Strombolian explosions.
After a few days, the rash becomes explosive type and form lava fountains 2-4 km high. The final phase is characterized by the formation of an eruption column sustained, high 5-15 km, which is followed by the collapse of the central part of the crater. The volcano then enters a resting phase that lasts several years. When he comes, the task starts again with outpourings of lava.
The last eruption of Vesuvius occurred in 1944 and the subsequent rest period, which persists to this day is much longer than the rest intervals that have occurred in the period 1631-1944, which lasted more than 7 years.
The 1944 eruption
On May 10, 1913, the bottom of the crater formed by the eruption of 19o6 sinks about 75 meters. As of July 5, 1913 the sinking is filled by an outflow of lava, thrown into the air and waste accumulate, forming a cone.
Between 1915 and 1920 the crater rises about 100 meters. The first overflow of lava out of the cone is 28 November 1926 and three years later, in June 1929, there was a violent eruption. After this eruption, Vesuvius alternates stasis and activities, mostly concentrated within the cone, for several years.
On August 12, 1943 at the foot of the cone opens a vent, whose activity causes the collapse of the cone, followed by explosions. On 6 January 1944, the flow of lava rises and lava flow poured out for going over 100 yards downstream. The lava continues to flow out of the crater until 26 January and within the same until February 23, the day when the effusive activity ceases altogether.
In the early hours of March 13, 1944 collapse of the walls of the cone and cease any activity until the afternoon of March 14, when re-launch of nuclear weak. In the night between March 17 and 18, with a massive collapse of the cone, again ceases all activity.
On the evening of March 18 will have new explosions followed by a copious emission of lava, which marks the beginning of the first phase ("Phase effusive" Imbo ', 1945) eruption of 1944. The lava overflows the rim crater at various points and reaches towards the north, the side from which the sum is diverted west to the Pit of Vetrana.
The blasts increase and the launch of slag and lava of up to 100 m. high above the crater rim. On the evening of 19 lava reaches the first houses of Massa and S. Sebastian, invades the villages and advancing up to 1.5 km from the center of Cercola, where he stopped on March 22.
From the morning of 19 explosive activity remains constant with tumultuous launches slag and lava up to 150 meters tall edge. From the evening of 18 in the morning of 19 will experience intermittent tremors and Vesuvius Observatory, from 10, 19, continuous tremors with intermittent reinforcement.
March 21 to 17 of the column of magma rises up to 2 km in height and begins the second phase of the eruption is defined, always Imbo ', "the fountains of lava."
The first fountain lasts 30 minutes and the molten lava, falling and accumulating on the outer slopes of the Gran Cono, gives rise to the pseudo-streams of waste. One of these, particularly large, is formed to the west-south-west where it reaches 700 m asl At I7, 30 returns an almost total calm with a significant reduction in explosive phenomena and the cessation of the quakes.
The eruptive pause lasts up to 20.10, when it begins to manifest a new lava fountain that lasts 20 minutes and has the same features as the previous. This is also followed by a general reduction of the eruptive activity. The alternating pattern of the eruption continues to repeat itself throughout the night and the morning of March 22. 8 successive phases of lava fountains, with the last one has the maximum around the eruptive paroxysm.
From 12 of March 22 there is a gradual change and, in addition to the hot material, is also emitted lithic material torn from the conduit. At this point begins the third phase of the eruption, that of "mixed explosions."
The pseudo-waste flows, the characteristics of the second phase, the following new flow phenomena called "glowing avalanches" and "hot clouds in miniature." The main flow is superimposed on the southern lava flow going, in seconds, for 2 km beyond the crater edge.
The central cone, being rebuilt by March 18, is joined on the afternoon of March 22, the inner walls of the Great Cone, reaching a maximum altitude of over 1260 m asl
At 21 of March 22, reproduce the explosions that lasted until the early hours of March 23, then decreased gradually. During the same day the lava will stop completely, the south stops at 350 m asl (The districts Monticelli-Voccole) and the north will stop at 120 m asl
At 12, 23, as explosions are in decline, are beginning to be felt Observatory with a growing number of earthquakes. The seismic crisis shortly before a new change in the eruption. In fact, by 14, are predominantly erupted ash and dark materials and begins alternating earthquakes and explosions.
Proceed with this phase, known by Imbo '"seismo-explosive", began a gradual reduction of the phenomena. On March 24 the continuous emission of ash that become clearer. On 27 and 28 explosions are increasingly rare and generally less violent, 29, the eruption may be considered closed. All activity is reduced to simple post-eruptive fumarolic exhalations.
Once the explosion, the walls of the crater and flanks of the Great Cone are starting to be affected by phenomena of adjustment. On 29 March the central crater has a depth of 300 m from the edge a perimeter of 1.6 km's west edge, the most affected by landslides, it appears to me the 1169 North-East at 1,300 m above sea level.
The edge of the crater although somewhat irregular, approaches, seen from above, the elliptical shape with the major axis of 580 m (East-West) and less than 480 m (North-South). For the continuous phenomena of landslide crater undergoes numerous changes in subsequent years.
The eruption comes shortly after the arrival of Allied troops in Naples. Because of the war, the Centre has become a weather station of the allies and its Director, Joseph Imbo ', is relegated to one small room from which it carries out its observations in the days of the eruption.
The event comes as a surprise the Americans and their cause more damage to an air raid, a whole flock of B29 bombers that was in the landing field near Terzigno is destroyed quickly from the ashes.
The Vesuvius seems to want to show it for the last time all of its power before returning to a rest that lasts to this day threatening. The only signs of activity are a few small earthquakes are constantly recorded by seismographs of the Vesuvius and the fumarolic activity is observed at the crater.