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Eruptions from
A.D. 79 to 1631 |
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Following the A.D. 79 eruption,
Vesuvio remained in an active state (an eruptive cycle) for maybe up to
1060 years. Documentation for that period is poor and therefore very little
is known about how Vesuvio behaved like in that period. From what little
information is available, though, it seems that the patterns of eruptive
activity differed considerably from those of the most recent active cycle,
1631-1944: Volcanoes of the World (1994 edition) lists eruptions from Vesuvio on the following dates:
Questionable eruptions are further listed for 991, 999, 1150, 1270 and 1347. An eruption in 1500, listed as a phreatic event in Volcanoes of the World, is believed by many authors to have been a very minor event, if an eruption at all. Of these eruptions, only seven unequivocally erupted lava, the first occurring in 968. At least two eruptions produced pyroclastic flows and surges. Average repose periods seem to be considerably longer than during the 1631-1944 cycle, but this may be an enhanced effect of poor reporting in that period. Possible smaller-scale, persistent Strombolian activity from the summit crater (that may have been lying somewhat hidden in a major caldera depression left by the A.D. 79 eruption) may have escaped recording because it did not significantly affect life around the volcano. Two longer eruptive periods reminiscent of 1631-1944 eruptive sub-cycles are reported for 222-235 and 379-395, but details are lacking about the sequence of events during those periods. There is also a notable (but possibly apparent) increase in eruption frequency beginning in 1007, coinciding with better reporting on eruptions in contemporaneous sources.
A.D. 472 eruption The A.D. 472 eruption was one of the most violent eruptions of Vesuvio in the past 2000 years, comparable to, if not exceeding, the 1631 eruption. Contemporaneous reports are scanty, but the event evidently had serious effects around the volcano. A reconstruction of the event has been made by Rosi & Santacroce (1983), confirming that it was highly explosive and devastating, sending pyroclastic flows and surges radially around the volcano, especially on its N side. It is noteworthy that the eruption was not a cycle-opening eruption like that of 1631, but occurred after only about 80 years of repose, if not even less, and was followed within about 35 years by another eruption that produced pyroclastic flows and surges, in 512.
According to Rosi & Santacroce
(1983), the first phase of
the eruption was sub-Plinian to Plinian, producing an airfall deposit
of greenish pumice with maximum thicknesses of 2 m on the NNE flank of
the volcano. At Avellino, 28 km to the E, this fall deposit is still 26
cm thick. The proportion of lithics increases towards the top. There are
two interbedded fine-grained ash layers in this deposit, grading laterally
into sandwave beds. During this phase, Vesuvio erupted about 1.6 x 10^8
m^3. The main fallout axis trends ENE from the volcano, similar to most
other Plinian and sub-Plinian fall deposits from the volcano. The notable fact that pyroclastic flows and surges from the AD 472 eruption occur mainly (?) in the N to NE sector of the Somma-Vesuvio volcanic complex has already been mentioned. It is an indication that in the case of violent eruptions with significant collapse of the eruption column, the Somma ridge does not present that much an obstacle to pyroclastic flows and surges, even though in the case of the AD 79 eruption it appears to have diverted similar but much larger flows and surges. A possible factor influencing the capability of the Somma ridge to block and divert pyroclastic flows and surges may be the position of the eruptive vent. In the case of a vent situated at the very base of the Somma ridge, pyroclastic flows would easily spill over that ridge once collapse of the eruption column occurs. However, computer models of a future eruption of a similar size to that of the AD 472 eruption have revealed that in fact, the ridge would essentially fail to act as a protective barrier (see Volcanic Hazards of Vesuvio). Little is known about the extent of destruction and fatalities caused by the AD 472 eruption. However, historical documents mention ash falls as far as Constantinople. Rosi & Santacroce (1983) believe that the eruption was in fact "extremely disruptive and must be considered the most violent and fatal [Vesuvian eruption] during the last nineteen centuries. A similar eruption occurring today [...] would have apocalyptic consequences."
A.D. 512 eruption Deposits of this eruption are not stratigraphically correlated with certainty, thus little can be said about the actual magnitude of the A.D. 512 event. However, contemporaneous sources describe "rivers of ash flowing like liquid, bringing hot sands {from the volcano}..." (letter by Cassiodorus, cited in Scandone et al. 1993a), easily to be interpreted as pyroclastic flows. No details are known about the extent of damage to inhabited areas but devastation of arable land and vegetation is mentioned in Cassiodorus' letter.
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Copyright © Boris Behncke, "Italy's Volcanoes: The Cradle of Volcanology" |
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set up in January 1996, last modified on 4 February 2000
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