Blocky, nonvesicular fragments of juvenile fragments point to some magma-water interactions at this stage (13). The eruption rapidly gained energy as more vents opened on the flanks of the cone ejecting pyroclastics at a growing mass eruption rate. Soon after the beginning of the eruption, a large eruption column rose up, attaining the famous shape of a pine tree.The height of the eruption column at this stage exceeded 20 km and may have reached up to 28 km, thus the eruption was Plinian.
Ash began to fall around the volcano about one hour after the start of the activity, but heavy block and scoria fall began at about 1000 in the direction of Ottaviano (north east side of Monte Somma), a village that later was to suffer from many other eruptions of Vesuvio. (12) During the morning of December 16, a continuous tremor began to be felt in Napoli, it did not cease until 8-10 hours later.
Darkness fell over the area around the volcano and reached Napoli at 4:00 on that fatal day. (13) The main portion of the eruptive plume was blown towards the east, causing darkness and tephra falls over southern Italy and over the Balkan.Slight asfalls are reported to have occurred as far as Constantinople, W Turkey, about 1250 km from the volcano. (12) The proximal maximum thickness of the initial pumice deposit is 1.5 m at Canale dell’Arena.
(8) After the initial plinian phase, between 7:00and 10:00 on December 16 the eruption took on a pulsating character, accompanied by strongly increased seismicity. During the night of 16-17 December, strong earth shocks occurred at intervals lasting 1-15 minutes. At about 2:00 on December 17 the first glowing avalanche that was observed to descend into the Atrio del Cavallo. At around the same time, strong rainfalls saturated large amounts of already fallen ash to form lahars that caused damage and disruption on the north and northeast sides of Mount Somma.(14) On December 17 the activity changed with occasional surges of sub-Plinian to Plinian activity that caused tephra falls around the volcano. On the 17th, the summit of the volcano was partially destroyed by the activity. (13) Within an active cycle, smaller sub cycles can be observed, starting with minor intracrateral (effusive and Strombolian) activity with some fluctuations until a strong eruption produces tall eruption columns, more voluminous, rapidly moving lava flows, and heavy tephra falls.This culminating, sub cycle-ending eruption is followed by a brief (max.
7 years during the most recent, and well-documented, cycle, 1631-1944) repose, then intracrateral activity starts again. (15). Typical eruptions closing Vesuvian sub cycles were those of 1767, 1779, 1794, 1822, 1872, 1906, and 1944. Each of them caused damage in the towns around the volcano and the people suffered partial or total destruction at least once during the 1631-1944 cycle. Torre del Greco, on the coast west of Vesuvio, was destroyed three times in that period.
Lava flows entered populated areas also during some more intense activity in the course of a sub cycle, most recently in 1929. Eruptions of this type have been seriously disruptive for life near Vesuvio in the past and would be extremely disturbing, were they to occur today. To cite one example: the 1906 eruption caused heavy tephra falls in the northeastern sector of Vesuvio, causing the collapse of almost all roofs in the towns of that area. Up to 500 people were killed in that event.
26 People died much the same way during the most recent eruption in 1944.(13) After that event, the volcano has most obviously entered one of the longer periods of repose that is maybe to last much longer – up to several centuries – until a new eruptive cycle will begin with a major explosive eruption. Such spastic eruptions produce heavy tephra falls, pyroclastic flows, surges, and lahars. Lava flows are uncommon during these events. As the next eruption will probably be a paroxysmal one, primary volcanic hazards are tephra falls and pyroclastic flows and surges. They form a significant threat for a zone including parts of Napoli and the entire belt of towns around the volcano.
It is certain phenomena, such as increasing seismicity, deformation, and others, will warn of an impending eruption, as has been the case before the AD 79 and 1631 eruptions. There are, however, serious logistical problems regarding the evacuation of maybe up to a million people in the areas endangered by tephra fall and pyroclastic flows and surges. Vesuvio has a long and complex record of eruptions. Eruptions before AD 79 have neither been recorded in historical documents nor are there any folklore of previous activity. For the first millennium after Christ the record is incomplete and only with the late 17th century it becomes reasonably adequate. We can say that the most recent eruptive cycle, lasting from 1631 until 1944, has been very well documented and gives an idea of the behavior of the volcano during such a cycle.Understanding of the volcano in longer terms of cycles is now beginning to form. It is known that eruptive cycles begin after non-active periods that may last centuries to millennia, and their opening eruptions are devastatingly violent, Plinian events.
The most famous one is the AD 79 eruption that has been so well described in the letters by the Pliny the Younger. His description inspired volcanologists in the late 19th century to call eruptions like that of AD 79 “Plinian” eruptions. Certainly the most notable aspect of Vesuvio’s eminence among Earth’s volcanoes is the dense population surrounding it and climbing higher and higher up its slopes. In an enchanting landscape with beautiful islands, magnificent mountain ranges, marvellous coasts and historically famed cities, Vesuvio is the focus, lying in the center of a plain on the east north eastern side of the Gulf of Napoli.It is the steepness, the sudden way it rises from its peaceful surroundings, which make it so impressive.
(16) Vesuvius is a very dangerous and deadly volcano. Mudflows and lava flows from the eruption in 1631 killed 3,500 people.(13) About 3,360 people died in the 79 A.D. eruption from ash flows and falls.(9) Studies of past eruptions and their deposits continue. These studies help volcanologists understand the hazards associated with future eruptions.
The population density in some areas of high risk is 20,000 to 30,000 per square km.About 3 million people could be seriously affected by future Eruptions. In the first 15 minutes of a medium- to large-scale eruption an area with a 4 mile (7 km) radius of the volcano could be destroyed (Dobran and others, 1994). About 1 million people live and work in this area immediately threatened by future eruptions. There are no signs of volcanic unrest at Vesuvius at the present time. (11) References (1.) V.
Arno et al., in Somma-Vesuvius, R. Santacroce, Ed. (Quaderni de La Ricerca Scientifica, Rome, 1987), pp.
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Geogr. Res. 1, 332 (1985). (5.) P. Papale and F.Dobran, J.
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M. Mantovani, R. Scandone, Bull.
Volcanol. 44, 317 (1981). (7.) Hoffer W (1982) Volcano: the search for Vesuvius. New York: Summit Books, p189 (8) Lirer L, Munno R, Postoglione I, Vinci A and Vitelli L (1997) The A.D.
79 eruption a future explosive scenario in the Vesuvian area: eveluation of associated risk. Bulletin of Volcanology 59: 112-124. (9) Barberi F, Rosi M, Santacroce R and Sheridan MF (1983) Volcanic hazard zonation at Vesuvius.In: Tazieffn H and Sabroux JC (eds) Forecasting volcanic events.
Developments in Volcanology I. Elsevier Amsterdam: 149-161 (10) Sigurdsson H, Carey S, Cornell W and Pescatore T (1985) The eruption of Vesuvius in 79 AD. National Geographic Research 1: 332-387 (11)Scandone R, Arganese G and Galdi F (1993b) The evaluation of volcanic risk in the Vesuvian area. Journal of Volcanology and Geothermal Research 58: 263-271 (12) Rosi M and Santacroce R (1983) The A.D.472 “Pollena” eruption: Volcanological and petrological for this poorly-known, Plinian-type event at Vesuvius. Journal of Volcanology and Geothermal Research 17: 237-248 (13)Rolandi G, Barrella AM and Borrelli A (1993a) The 1631 eruption of Vesuvius.
Journal of Volcanology and Geothermal Research 58: 183-201 (14)Scandone R, Giacomelli L and Gasparini (1993a) Mount Vesuvius: 2000 years of volcanological observations. Journal of Volcanology and Geothermal Research 58: 5-25 (15)Mastrolorenzo G, Munno R and Rolandi G (1993) Vesuvius 1906: a case study of a paroxysmal eruption and its relation to eruptive cycles. Journal of Volcanology and Geothermal Research 58: 217-237 (16) Santacroce R (1983) A general model for the behaviour of the Somma-Vesuvius volcanic complex.
Journal of Volcanology and Geothermal Research 237-248 (17) Albitino Elio, Vesuvio; a volcano and its history. Naples Usmate Press.3-24 Barberi F, Macedonio G, Pareschi MT, Santacroce R (1990) Mapping the tephra fallout risk: an example from Vesuvius, Italy.
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