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Precursors of eruptions at Vesuvius (Italy)
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Journal of Volcanology and Geothermal Research 171 (2008) 191 – 200 www.elsevier.com/locate/jvolgeores
Research paper
Precursors of eruptions at Vesuvius (Italy) Roberto Scandone ⁎, Lisetta Giacomelli Dipartimento di Fisica, Università Roma Tre, Via Vasca Navale 84, 00146, Roma, Italy Received 1 August 2007; accepted 14 November 2007 Available online 4 December 2007
Abstract The historical record of activity of Mount Vesuvius is uncommonly long and may serve as a guide to understand precursors before the outbreak of new activity. Reposes of different lengths have been observed in the past, with long ones preceding violent explosive eruptions. Eruptions occurring during periods of permanent activity have been preceded by possible deformation of the volcanic edifice and by short duration, earthquake swarms. Otherwise they have occurred without any reported precursors. The renewal of activity after long periods, like the current one, has been preceded by unrest lasting years to weeks, as a new eruption would require connection to the surface of a reservoir at depth ranging between 6 and 4 km. Since 1944, episodic seismic swarms, have occurred with a frequency similar to that of the violent strombolian eruptions during the last period of permanent activity; they are interpreted as intrusions and arrest of magma batches into a reservoir at the same depth of that feeding past sub-plinian eruptions. © 2007 Elsevier B.V. All rights reserved. Keywords: Vesuvius; precursors; eruption
1. Introduction Mount Vesuvius is located in Southern Italy near the city of Naples in an area with one of the highest densities of population in the world. The volcano is built at the crossing of NW–SE, and NE–SW trending, oblique-slip faults, and E–W trending normal faults (Fig. 1) (Bianco et al., 1998). The NE–SW trend is also evidenced by the Differential SAR Interferometry (DInSAR), (Borgia et al 2005), showing that the SE sector is moving to the E relatively to the NW sector, and by seismic reflection profiles in the bay of Naples (Finetti and Morelli, 1974). Bouguer gravimetric anomalies of the volcano provide evidence of a shallow denser structure without very deep roots (Cassano and La Torre, 1987). A prominent high–density core has been also identified by seismic tomography (Zollo et al., 1996) concentric with the caldera structure. Seismic tomography also shows an extended low velocity layer at about 8–10 km
⁎ Corresponding author. E-mail address: [email protected] (R. Scandone). 0377-0273/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jvolgeores.2007.11.018
depth, interpreted as the top of a magma reservoir, having a surface area of at least 400 km2 (Auger et al., 2001). The last eruption of Vesuvius occurred in 1944, and, since then, only episodic swarms of earthquakes have characterized its state of activity. A repose of such length is unusual within the record of activity since 1631 (Carta et al., 1981), but is not unusual in the longer historical and geological record. A long period of quiescence, lasting possibly since 1139AD (uncertain eruptions are reported in 1306, Principe et al., 2004, in 1500 and 1571, Guidoboni and Boschi, 2006), ended on the 16th of December 1631 with a sub-plinian eruption. Also before the eruption of 79 AD there was a long period of quiescence lasting since many centuries, if we consider as a false event the 216 BC eruption quoted by Stothers and Rampino (1983). A few Greek and Roman scholars (Strabo, Diodorus Siculus, Vitruvius, Vergil) recognized the volcanic nature of the mountain before the eruption of 79 AD without reporting historical eruptions. Long periods of quiescence at Vesuvius ended with explosive eruptions (Plinian or sub-plinian) (Santacroce, 1987) as well as with effusive or mildly explosive eruptions (Arrighi et al., 2001). Currently it has been suggested, that the most
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Fig. 1. Simplified structural map of Vesuvius (modified after Bianco et al., 1998).
likely event in case of renewal of activity is a VEI = 3 eruption; more violent eruptions have a lesser probability (Scandone et al., 1993; Marzocchi et al., 2004). Given the high number of people (more than 500,000) living in the immediate threat of even a small sized eruption, it is of paramount importance to understand the nature of phenomena that may precede the outbreak of activity and provide a sufficient time to adopt precautionary measures of evacuation. In order to provide such data we revised the historical and recent reports of activity of Vesuvius to identify precursory signs and the possible style of a future activity. 2. Precursors after long repose periods The presence of extensive palesols below the deposits of plinian and sub-plinian eruptions at Vesuvius suggests long periods of quiescence before these events (Delibrias et al., 1979; Principe et al., 2004). One such event was the eruption of 79 AD, which destroyed the cities of Pompeii, Herculaneum and Stabiae. The poet Silius Italicus reports evidence for an eruption of Vesuvius in the poem “Punica”, in coincidence with the defeat of Romans by Hannibal at Cannae (216 BC). It is however doubtful that such an eruption may have occurred without any other reports from contemporary sources of the period, who describe many battles fought in the following years at the foot of
the volcano such as those at Nolae and Nuceria. It is more likely that Silius Italicus, who lived in Naples in his late years after the eruption of 79 AD, may have actually seen the eruption and might be willing to give a poetic account of it in his epic poem. Diodorus Siculus (80–20 BC) reports that the Campanian plain was called “Phlegrean (“fiery”) from the mountain which of old spouted forth a huge fire as Aetna did in Sicily; at this time, however, the mountain is called Vesuvius and shows many signs of the fire which once raged in those ancients times.” Collectively all Roman and Greek authors do not provide any strong evidence that during their time (since VIII–VII century BC) there was any eruption of Vesuvius; instead they report several eruptions on Ischia island where archeological and geological studies confirm the historical reports. The most recognized naturalist in imperial time: Pliny the Elder did not include Vesuvius in any list of volcanoes, so we may confidently assume that the volcano had been quiescent since several centuries before the 79 AD eruption that killed him. The first signs of unrest occurred a few years before the eruption. Seneca reports that a major earthquake occurred on 5 February of 62 AD. The earthquake flattened Pompeii, made great ruins in Herculaneum, and caused minor damage in Nuceria and Naples (Fig. 2). The aftershocks lasted for several days until they became milder “but still caused great damage”. Cubellis and Marturano (2006) suggest that the earthquake
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Fig. 2. Basrelief found at Pompeii remembering the earthquake of 62 AD (Naples, National Museum).
occurred below Vesuvius and had a magnitude of 5.1–5.4. Cubellis et al. (2006, 2007) suggest that there was also another major earthquake in 64 AD, which caused damages in the Vesuvian area, and scared Emperor Nero during a performance in Naples theatre. The psychological shock caused by the earthquakes to local inhabitants was so serious that it compelled Seneca to write his treatise on Natural Phenomena (Naturales Questiones) to support his friend Lucilius living in the area. The results may have proven more successful than desirable. Immediately before the eruption of 79 AD, earthquakes occurred for some time, but were disregarded by local inhabitants because of their familiarity with the phenomenon. As the Younger Pliny testified, “for several days before (the eruption) the earth had been shaken, but this fact did not cause fear because this was a feature commonly observed in Campania”. Extensive repair works were underway in many houses at Pompeii and Oplonti, and Boscoreale before the occurrence of the eruption (Fig. 3). We regard this as an evidence of the intensive seismic shaking due to a prolonged period of seismicity. A long period of repose, lasting at least 150 years, preceded the sub-plinian eruption of 1631. Several months before the beginning of the eruption, people near the volcano felt some earthquakes (Braccini, 1632). They were not particularly scared because earthquakes from the nearby Apennine chain were often felt in the area (a large one had occurred four years before in Apulia, in 1627). Incidentally, Braccini (1632) uses the same words as Pliny the Younger, for the attitude of the inhabitants to prolonged periods of earthquake swarms. The seismic activity became more severe in the few days before the eruption. According to Braccini (1632) the signs of an impending eruption were so evident that people should not have disregarded them but “Perituri non recipunt consilia” — (“those that are to die, do not accept advice”). Bertagnini et al. (2006) provided a detailed reconstruction of the precursors basing on contemporary chronicles. They report that rumbles, landslides in the crater and on the flanks of Somma were observed from September 1631. Since the end of November, muddy well water and salinity variations were observed in the springs at the foot of Vesuvius. Deformation and fracturing on the flank of the volcano occurred some days before the eruption. Braccini (1632) reports that at least 15 days before the eruption, the crater had been filled (possibly by landslides or piston-like uplift of the crater
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floor) and could be crossed from one side to the other. On 11 December, the vegetation inside the crater was burnt and there was a strong sulfur smell. A continuous rumbling was felt by the inhabitants of Torre del Greco, Resina (Ercolano) and S. Sebastiano since 10 December. Starting from the night before the eruption, a significant increase of seismic activity occurred, culminated, few hours later with the onset of the eruption (Bertagnini et al., 2006). Cubellis et al. (2006) suggest that the maximum magnitude of the earthquake swarm was 4.2. This activity culminated on the morning of 16 December 1631 with the opening of a new vent on the SW flank of the volcano and the development of a devastating explosive eruption, which destroyed all the villages at the foot of the volcano and caused 4000 deaths. The eruption left such an impression on contemporaries that the Spanish Vice—King of Naples, Emmanuele Fonseca, ordered the engraving of a memorial stone with a warning to posterity which is still now compelling: “…Sooner or later the mountains will burn again, but before, will moan, tremble and shake the ground, and smoke and flames and lightning will flash across the sky, then sounds and thunders will drive the inhabitants away...”. 3. Precursors during persistent activity The eruption of 1631 started a period of persistent activity, punctuated by violent strombolian eruptions that lasted, with
Fig. 3. Repairs works made in Pompeii, and nearby villages immediately before the burial of the town during the 79 AD eruption of Vesuvius, provide evidence of an intense seismic swarm preceding the eruption by a few days, as testified by Pliny the Younger. The arrow show a pole sustaining the lintel of a door of a country “Villa” at the foot of Vesuvius (Boscoreale) buried during the eruption.
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Fig. 4. Frequency of different precursor types observed during the period 1631– 1944.
a few breaks, for more than three centuries until 1944. The survivors of the eruption of 1631 re-established new settlements at the base of the volcano, on the same places destroyed by pyroclastic flows and lahars and became accustomed to its milder activity. A few individuals (mostly belonging to the ecclesiastic or noble classes) started to maintain detailed chronicles of its activity and to report the events, recording also subtle changes, precursory of some notable eruptions. These signs included abnormal seismic activity, variation in the depth and state of the water table, retreat of the coastal line, and failures of the conelet built inside the cone. We report in the Appendix, in Table A1, a summary of all these precursors extracted from an accurate analysis of contemporary sources. The results are summarized in Fig. 4. The most frequent precursor, observed in the 70% of all the reported cases (31), is the occurrence of seismicity; the second most observed precursor is the collapse of the conelet inside the crater possibly due to extensional phenomena preceding the magma ascent. The 1929 and 1944 eruptions were the only ones monitored with a seismograph (Imbò, 1949). The peculiar phenomenon,
that preceded by a few days the eruption of 1944, was the collapse of the conelet built inside the crater during the persistent activity of the preceding years. The collapse occurred on the 13th of March 1944, and was accompanied by a sudden drop, with respect to the value of the previous days, in the amplitude of harmonic tremor (Fig. 5). The emission of a lava flow on the 18th of March was accompanied by the increase in the amplitude of tremor. The collapse of the conelet and the drop in the amplitude of tremor were interpreted by Imbò (1949) as a drop in the height of the magma column. A closer analysis of the historic records indicates that other phenomena, like changes of the water table and sea retreat, probably related to deformation of the volcanic edifice, have commonly been observed from days to weeks before the eruptions. The variation of the level of water table has been observed also on other volcanoes either before eruptions or periods of unrest (Newhall et al., 2001). Earthquakes and collapse of the conelet, built inside the summit crater, were generally observed mostly in the few days preceding the eruption. It must be recalled that the reported earthquakes refer only to those felt by the inhabitants of the Vesuvian area, which, basing on current instrumental records, must have a magnitude higher than 2.0. A magnitude 3.5 is widely felt all over the Vesuvian area, and a magnitude 4.5 can cause slight damages in Naples (Cubellis et al., 2007). The decrease in the level of the water table is commonly reported in the areas nearby the villages of Resina (present Ercolano) and Torre del Greco (e.g. Alfano and Friedlander, 1929; Palmieri, 1862). In the same area were also observed retreats of the sea and, in one case (1861), a ground uplift of 110 cm (Palmieri, 1862). The three eccentric eruptions of 1760, 1794, and 1861 were all preceded by a seismic crisis lasting three days. The 1760 eruption occurred during a period of persistent activity with strombolian explosion at the summit crater. At the end of November 1760, there was a decrease of the intensity of strombolian activity, with a subsequent sudden increase at the beginning of December. On 12 December strong explosion were heard also in Naples (13 km from the summit
Fig. 5. Amplitude of the tremor measured by an Omori–Alfani seismograph operating at the Vesuvius Observatory since 1914. The amplitude has a sudden drop in coincidence with the collapse of the conelet built inside the cone.
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cone). At 5 pm of 20 December, many small earthquakes were felt in the villages at the foot of the volcano, and at 7:30 pm of 23 December, a strong shock and a continuous tremor accompanied the opening of an eruptive fracture on the south flank at about one and half mile from the main road along the coast. Again at 8:15 pm, a new strong shock accompanied the opening of another vent at a lower altitude. The eruption of 1794 was preceded by a period of quiescence lasting since at least 9 months (Russo, 2002). A decrease in the level of the water table occurred weeks to days before the eruption, and rumblings were heard in the last 2–3 days before the eruption (Russo, 2002). Intense seismicity was felt only 3 days before the eruption with an earthquake strongly felt over a wide area especially to the NE of the volcano and in the nearby Apennines. The earthquake occurred on 12 June 1794, at 21:15 and was felt as an undulatory movement and did not cause any damages in the towns surrounding the volcano, so we infer that it may have been relatively deep, or of tectonic origin in the Apennines. Other shocks were felt at 01:00 and 08:00 of the 13th (Breislak and Winspeare, 1794). The inhabitants of Torre del Greco felt many earthquakes between the 12th and the15th of June, along with a mild continuous shaking of the ground. The people living in Naples felt only the first earthquake occurred on the 12th (Breislak and Winspeare, 1794). The eruption was preceded by a two-hours long, intense, seismic swarm at 21h, on the15th of June, immediately before the outbreak of a fracture, which opened on the lower flank of the cone immediately above Torre del Greco. A lava
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flow issued from the fracture and, after a few hours, invaded and completely destroyed the town (Fig. 6). The eruption of 1861 followed a 2 years long eruption began in 1858 and ended on April 1861. This was the first one monitored with a seismograph built by G. Palmieri, Director of the newly built (1841) Vesuvius Observatory (Palmieri, 1862). An uplift of the ground of 110 cm preceded the eruption, and on 5 December 1861 there was a strong felt earthquake and the spilling of water wells in Torre del Greco. The water had a temperature of 38°C and was rich in CO2. During 5 and 6 December, there were many light shocks recorded by the Palmieri seismograph and on 7, they were also felt in the villages at the base of Vesuvius. At 9:00 am of 8 December, there was the intensification of the earthquake swarm and of rumblings. At 16:00, the opening of lateral vents at an altitude of 290m asl and a set of SW–NE trending fractures through Torre del Greco caused the destruction of many buildings. A small lava flow reached the outskirts of the town (Palmieri, 1862). Unfortunately, after this eruption there are no more reports of water well anomalies, possibly because of the increasing major attention paid to scientific instruments deployed at Vesuvius Observatory. Not all the eruptions, occurred during this period, were preceded by significant seismic activity and not all eruptions have been preceded by other observed precursory phenomena. Actually, many of them have been practically silent. Mercalli (1905) notes that many paroxisms are actually preceded by long periods of reduced activity. However, several others (e.g. 1872) have been preceded by periods of increased strombolian activity. For example the eruption of 19 October 1767 was preceded by an increased strombolian activity that caused a marked increase in the height of the scoria cone built within the summit crater. Often, reawakening after the short periods of repose between 1631–1944 occurred with mild activity like in 1875 or 1913. The 7 years long repose after the eruption of 1906 ended in 1913 with only a few recorded earthquakes (Mercalli, 1913) and the formation of a collapse pit inside the crater left by the previous eruption; these phenomena were followed by a quiet emission of lava inside the collapse pit (Malladra, 1923). 4. Discussion and conclusions
Fig. 6. The initial opening of a lateral fracture on the SW flank of Vesuvius during the 1794 eruption (by Saverio della Gatta, private collection).
Marianelli et al. (2005), Scandone et al. (in press) suggest that the permanent activity of Vesuvius between 1631 and 1944 was fed by a magma accumulating at shallow depth within the volcanic edifice. The violent strombolian eruptions were caused by episodic, multiple arrivals of discrete batches of magma rising faster and not degassing during the ascent (Scandone et al., 2007). The rapidly ascending magma pushed up the liquid residing in the shallow reservoir, caused fracturing of the upper volcanic edifice, and eventually reached the surface with its full complement of volatiles, producing fast lava flows and kilometer-high lava fountains. The precursors observed during this period signal the complex interaction between the shallow residing magma responsible for the persistent activity and the arrival of the fast multiple ascending batches, which cannot be accommodated in the
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shallow plumbing system. The water table of a volcano can be regarded as a proxy of a dilatometer as it is strongly related with strain changes within the volcanic edifice (Newhall et al., 2001). During the period 1631–1944, all the anomalies of the water table (but the one in 1861) report a drop in the level of water wells in areas near the villages of Torre del Greco and Ercolano. This area is a on a NE–SW trending, normal fault crossing Vesuvius (Fig. 1) (Finetti and Morelli, 1974; Bianco et al., 1998). The lateral vents of the eruptions of 1631, 1794 and 1861, as well as pre-1631 lateral vents (Sorrentino, 1734) opened along this fault which is believed to be the main fracture feeding the activity of the volcano (Scandone et al., in press). We suggest that the intrusion of magma batches at shallow depth may cause a dilation perpendicular to the direction of this fault with creation of voids and drop of the level of water table. Multiple intrusions may eventually cause the fracturing of the flank of the volcano, signaled by the precursor seismicity with the sudden drop of the magma column residing in the top of the edifice and the collapse of the conelet. Alternatively, such phenomena may be interpreted as related to an external tectonic trigger. In this case, dilational strain accumulation on the NE– SW fault, signaled by water well changes, causes the arrival of fast ascending magma batches, which fracture the upper flank of the volcano. This pattern ended in 1944 because of the progressive cooling of the magma residing in the shallower part of the volcano (Scandone et. al, in press). Such circumstance is also supported by the seismic tomography evidencing a region with an anomalous high-velocity of propagation of seismic waves, which starts from about 400m below the crater and extends down to at least 3000m. The highest velocities 3.8–4.0km/s are observed about 1500–2000m below the surface (Zollo et al 1996, 1998; De Natale et al., 1998). These authors interpreted the anomaly as due to a plexus of solidified dykes. The cooling of magma residing in the shallow reservoir is responsible for the present period of quiescence longer than any observed between 1631 and 1944. Such repose has a length smaller than that before 1631, but comparable with other reposes occurred during the Middle Age (Alfano and Friedlander, 1929). Renewal of activity after long quiescence periods has occurred often with violent sub-plinian or plinian eruptions fed by magma accumulated in a shallow reservoir at a depth of the order of 3–6 km (Barberi and Leoni, 1980; Santacroce, 1987). During the present repose, significant thermal anomalies were observed from 1952 to 1954 with an increase in the temperature of fumaroles within the crater from 350 to 600°C (Imbò et al., 1964a), and again on 11 May, 1964, with a widely felt shock (Imax = 5 Mercalli Scale at the foot of Vesuvius) (Imbò et al., 1964b). Since then, the temperature of the fumaroles has decreased (Nazzaro, 1997). Major seismic crises occurred in 1978–80, when there was a swarm of moderate earthquakes (M b 3). The most significant earthquake since 1964 occurred in 1999 with Md = 3.6, accompanied by a relatively small number of earthquakes with Md N 1.8 (De Natale et al., 2006). Since 1985–86, there has been a progressive decrease of the b-value of the earthquakes, an alternating sequence of seismic quiescence and activity, and an increase in the observed earthquake
magnitude (De Natale et al., 2004, Bianco et al., 1999). The source mechanisms of the major earthquakes are compatible with isotropic components that indicate volumetric expansion (De Natale et al., 2004). The average depth of the earthquakes is comprised between 2 and 6 km (De Natale et al., 1998; Lomax et al., 2001; De Natale et al., 2006). The recurrence rate of seismic swarms or thermal anomalies in the past 50 yr is = 0.14yr− 1, similar to the recurrence rate of paroxistic eruptions evaluated until 1944 (0.13yr− 1) (Scandone et al., in press). We infer that the episodic occurrence of seismic crises is suggestive of discrete episodes of magma intrusions in the same zone that fed the sub-plinian eruptions in the past (Fulignati and Marianelli, 2007). Seismicity occurs when the added, magma volume cannot be accommodated by aseismic compression of surrounding rocks, and spreading of the volcano (Borgia et al., 2005). We suggest that a catastrophic failure of this reservoir and the migration of magma to the surface is likely to be accompanied by a significant seismicity increase in the zone above it: namely in the top 2–3 km of the volcanic structure presently not greatly affected by seismicity. The intensity and magnitude of a future eruption depend on the ratio between the cooling rate of ascending batches and their feeding rate into the shallow reservoir. It is currently not possible to estimate the duration of possible future precursors basing only on the past history of the volcano. The earthquakes before the eruption of 79 AD lasted for decades (Cubellis et al., 2006, 2007). This circumstance is also confirmed by the timing of multiple intrusions into the magma chamber that fed the eruption. Morgan et al. (2006) ascribe the resorption of Ba-poor crystal rims of the sanidine in the products of the eruption, and re-growth of Ba-rich rims to the intrusions of hot magma batches in the century preceding the eruption with a significant magma recharge 20 yr before 79 AD, close to the 62 AD earthquake reported by classical authors. Such extended periods of anomalies may cause a major problem in the planning of measures for the reduction of the risk, which could require mass evacuation of the areas subject to the eruption treat. Volcanic unrest at quiescent volcanoes may not be immediately followed by eruption, but may represent a build up to critical conditions. There is no certainty that the build up follows a linear, or a time predictable trend as it may be related, as the past history shows, to episodic pulses into a magma chamber. Currently there is no rule for establishing a critical threshold, unless gathering a more detailed knowledge of the stress state inside the volcanic edifice and an average magma supply rate into it. The replies to these questions may require the drilling of exploratory wells into the roots of the volcano, which in terms of cost-benefit analysis, may not represent an impossible task in the near future. Acknowledgements J.C. Tanguy and Chris Newhall made useful comments to an early draft of this manuscript. We acknowledge partial financial support from INGV and Dipartimento Protezione Civile Nazionale of Italy, and MIUR-Prin Project 2005 (Risalita dei Magmi e Dinamica delle Eruzioni).
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Appendix A Table A1 Precursors of eruptions and renewals of activity in the period 1631–1944 YEAR
Observed phenomena
Notes
Eruption
1631
1660
Seismicity, deformation, and landslides at crater, fumaroles increase Earthquakes
In the early morning of the 16th December opening of a fracture on SW flank of volcano and beginning of explosive eruption Explosive eruption on 3 July 1660
1682
Earthquakes
1694
Earthquakes; Collapse of Conelet
1696
Earthquakes
1697
Earthquakes
Few days before the eruption are reported earthquakes and rumblings felt in the villages around Vesuvius. Strong seismic crisis in the night preceding the eruption (see details in the text) An earthquake swarm felt at Ottaviano on the 3rd of July hours before the start of the eruption Since beginning of August: earthquakes and rumbling felt at Torre del Greco Since March: seismicity felt in Torre del Greco. On 12 March strong strombolian activity, explosions and earthquakes. On 5 April explosion and collapse of Conelet. Earthquakes and explosions since 31 July lasting till 4 August 1696. Earthquakes on 15 September
Explosive Eruption starts on 12 August, 1682 Lava flows begins on 13 April (lasts for 15 days)
Lava flows starts on 4 August (10 days)
Fracturing of the cone and lava flow on 19 September for 8 days 1698 Earthquakes, Rumbles On 14 May, the sea retreats 5 times along he coast of Torre del The lava flows starts on 25 May and last until 2 June. and sea retreat Greco. On 19 May, earthquakes and rumblings with stronger Explosive activity since 7 June. explosive activity. 1705–1706 Earthquakes Earthquakes felt between 19 January 1705 and 20 July 1706 Frequent explosions 1707 Earthquakes Since July, felt earthquakes and small lava outflows, Explosive activity and emission of a lava flow on 29 July. increasing on 28 July with the opening of a fracture on the Eruption ends 18–22 August SW flank 1723 Earthquakes, Water Since 18 March, decrease of water table in Torre del Greco Explosive activity at the crater between April, 20 and June 25, Table, Sea Retreat and sea retreat for three times. On 29 March, felt earthquakes. The eruption begins on 25 June with the emission of a lava Strong seismic activity on 30 June flow and strong explosive activity between 2 and 4 July (eruptive cloud like “a giant black pine tree” 1730 Sea Retreat, water table Intra-crateric activity since 27 February. Explosions since 2 Strong explosions on 24–25 March and collapse of crater on March and lava flow 17–23 March. On 23 March, sea retreat 25 March with strong explosions and the emission of a fast and decrease of level in water wells at Torre del Greco lava flow. Eruption ends on 1 April 1737 Water table, earthquakes Before eruption, decrease of water in wells at Somma. Water Eruption begins on 19 May. Strong explosions on 20 May with acidulous flavour and sulfur smelling. On 17 March felt with earthquakes that caused some collapses in Naples. On 21 earthquakes. Increase of strombolian activity and a giant May a fast lava flow from the flank of the volcano reached the eruption cloud on 15 May. After the eruption: Mofettes and sea coast and partially destroyed Torre del Greco for the first time since 1631 acid water in wells 1751 Earthquakes On 22 October an explosion felt in Ottaviano, on 23 October The eruption begins on 25 October with the fracturing of the at 5:30 pm, an earthquake felt in Naples SE flank of the cone 1756 Sea retreat On 23 June, sea retreat at Castellammare, and again on 9 On 12 August a lava flow toward Torre del Greco, and, on 12 August August, 2 lava flows toward Portici 1760 Earthquakes Felt earthquake swarm between 20 and 23 December. Beginning of eccentric eruption on 23 December at 19:30, on Stronger earthquakes since 17:30 of 23 December (see southern flank details in the text) 1770 Water table Lowering of water table at Volla and Torre del Greco before On 15 February 1770, explosive activity and felt tremor. On eruption. 16 March, earthquakes 16 March fracturing of the E flank of the cone and emission of lava. Again in April lava flows toward: Il Mauro and Boscoreale 1779 Earthquakes Felt earthquakes during July 1779. Increase of strombolian Explosions and eruptive column on 3 August. At the same activity at the end of July and small lava flows. Felt tremor at time opening of an eruptive fracture on the Nortern flank of 7:30 pm of 3 August the cone. On 5 August: explosion and collapse of the upper part of the crater. On the night between 7 and 8 August, violent explosive paroxism 1794 Earthquakes, water A tectonic earthquake on 12 June strongly felt at Avellino. On At 21 of 16 June, strong earthquake with an explosion and a table, rumbles 15 June numerous earthquakes felt around Vesuvius fracture on the SW flank of Vesuvius. A fracture propagates especially in the 2 h before the eruption. These quakes were upward and downward. Lava from the SW fracture invades hardly felt in Naples. Months to days before the eruption Torre del Greco, and reaches the sea. A lava flow issues from drying of water wells at Resina, Pompei; more evident since another fracture on the NE of the cone, and goes toward Torre 13 June. The water comes back after the eruption. Rumbles Annunziata and Il Mauro. On 17, increase of ash emission and collapse of the cone. Explosions until 18. On 20, strong heard since three days before the eruption earthquake and another collapse of Gran Cono. 1804 Earthquakes, water On 31 July, drying of water wells in Resina and Torre del Since 15–8, a lava flow toward Camaldoli, which stops on 30 table, sea retreat Greco and sea retreat between Torre del Greco and Torre September. On 2 September, the lava flow is at Monticelli. On Annunziata. On 11 August, felt earthquakes at Resina. 16, the lava stops at 0.3 mile from the Royal road. (continued on next page)
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Table A1 (continued ) YEAR
Observed phenomena
Notes
Eruption
1806
Earthquakes
Earthquakes felt at 2:30 am of 31 May
1813
Tremor and rumbles
Tremor and rumbles felt at 10 am of 25 December
1822
Water table, earthquakes Drying of water wells in Resina during September in coincidence with the opening of a new small vent within the crater, where there were already two other vents in strombolian activity. Increase of strombolian activity between 15 an 21 October. On 20–21 October, small earthquakes felt within 8 miles from the crater. At the same time there was a strong increase in the emission of black smoke. On 21 effusion of a lava flow from the summit crater.
1834
1850
Water table, earthquakes, collapse of conelet Water Table
Drying of water wells in the villages around Vesuvius. On 23 August, strong earthquake and collapse of the bottom of the crater. Decrease of water table observed on 23 January at Resina and Torre del Greco
1855
Rumbles
Rumbles heard during the night of 30 April in coincidence with the opening of a fracture on the N side of the cone. Variation in water table after eruption.
1861
Earthquakes, inflation
Strong earthquake felt on 5 December at 9 am. On 5 and 6 shocks recorded at Vesuvius Observatory, more numerous on the 7th when they are felt at Torre del Greco. At 8 am of 8 December, felt seismic activity at Torre del Greco increasing in intensity till 3 pm. On 8 December, inflation of the coast (1.1 m at Torre del Greco). Increase of water table during and after the eruption
1889
Collapse of conelet
Explosion and lava fountain at 2.30 am, on 31 May. Strong explosion at 3.15 pm. On 1–6,at 4 am, a lava flows to SW and W; one toward Camaldoli travels 3.5 miles in 1 h. Another flow reaches the sea near Torre del Greco. Eruptive cloud during the evening. New lava flow, 7 miles long, on 2–6. On 3, explosive activity. Activity until 9 June. At 2:00 pm of 25 December, explosion with eruptive cloud and lava toward Fosso Bianco; another flow toward Viulo; explosive activity and lava flows in January and February 1814. On 22 October (1 am), fire column on the crater, 2000 feet high; fracture of the cone to the E with a glowing avalanche. Outflow of lava at dawn, toward SW. After the lava emission, ash column toward SE. Decrease during the morning, and increase at 13 h, with tremors and a high column, at 16 h, strong explosion with emission of lava from E side. During the night, opening of new vents in the crater and on the flank toward Camaldoli; on 23 October (1 h), new explosions with an high eruptive column and strong tremor; collapse of part of the crater; 2 eruptive columns: white at W and dark at E. On 24 October, ash–fall; continuing activity with decreasing intensity until 16 November. Eruption column on 23 August, on 24 August, 4 vents on E flank of the crater; and, on 28–29 August, a lava flow toward Poggiomarino. Fracture along N side of the cone on 5–February; rapid lava flow into Atrio del Cavallo and then to E. On 7 and 9 February, increase of lava flow toward il Mauro and Poggiomarino. On the 9th, dense smoke from the crater with ash–fall on Torre Annunziata. Decrease of activity on 10 February; from 12 to 15, lapilli and, on 16 at 12,30, two strong explosions. Opening of vents on the N side of the cone with lava emission and mild strombolian activity. Lava flow into Atrio del Cavallo toward W to Vetrana, and Fosso del Faraone. During the night it reaches S. Sebastiano and Massa di Somma. New flows on 6–5 and 7–5 reach S. Sebastiano and Somma. On 8– 2, the lava flow arrives at 1/2 mile from Cercola. At 4 pm of 8 December, a fracture forms at 2 km above Torre del Greco at 290 m asl. The fracture trends ENE–SSW and extends into the sea.Conelets form since 4 pm in the higher part of the fracture with lava flow toward Resina and Torre del Greco. Smoke and mild explosions at the crater. Damages to the buildings of Torre del Greco because of the fracture; Earthquake on 11-1 and 16. On that day, at 8 am, boiling of the sea at 1500 m in front of Torre del Greco. Same phenomenon on 17-12, at 9 am. On 17-12, at 1 pm, eruption column at the crater, also during the night of 23-12, ash emission lasts until 31-12. Lava flows till September
1895
1903
1906
On 1 May collapse of conelet and opening of a fracture on the cone Earthquakes, collapse of On 3 July 1895 earthquakes accompanying the fracture of the On 3 July1895, fracturing of the WNW side of the cone with conelet cone. Collapse of the conelet on 3–4 July of 1895 new vents at 1185, 1100, 900 and 750 m asl. Lava flow from the lower vents into Fosso della Vetrana. Lava is emitted for all the year. On November 1895, the summit crater is 250 m deep. During September 1897, the depth of the crater decrease of 100 m due to landslides. At the beginning of July 1898, the crater is 60 m deep. The lava dome formed during this period is called Colle Umberto. Collapse of conelet On 22 August 1903 collapse of conelet and crater On 26 August, fracture on the Crater at WNW, explosion and lava flow onto Colle Umberto. On 27, fracture trending ENE at 800 m asl with lava flow. Collapse of 130 m of the crater with vulcanian explosions. Collapse of conelet, On April 4, black smoke and partial collapse of the cone (5,30 On 5–4, violent explosions and lava emission; on 6, at 8 am, earthquakes am); new vent at 1200 m on S flank of Gran Cono; lava; vent on SE flank of crater at 600 m asl; lava; intense activity at
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Table A1 (continued ) YEAR
Observed phenomena
1906
1911–1913 Collapse pit
1929
Earthquakes and collapse of conelet
1944
Collapse of conelet
Notes
Eruption
seismic activity; (14h) collapse of conelet; explosive activity the crater; (24: h) increase of seismicity. On 7 April, new vent from strombolian to vulcanian; on E flank, and lava toward Terzigno; outflow at the central crater; at 7 pm, explosions with incandescent ejecta up to 1–2 km above crater; 9 pm, explosion with fragmentary material; 11 pm, new lava emission; 8, at 030 am, strong explosions and earthquake; (2:30 am) violent earthquake with explosion and emission of ash, incandescent material and lithics. In July 1911, landslides within the crater. On 10 May 1913 a The volcano had been in a quiescent stage since the end of the collapse pit inside the crater with smoke issuing from it. eruption of 1906. Since July 1913, red glows in the crater and progressive lava filling of the collapse pit. Since 27 May, no activity. On 31-5, moderate strombolian On 3 June, rapid lava emission, out-flowing to E. Scoria activity until 2–6. At 3 pm of 2–6, frequent earthquakes. On ejection up to 300 m. Since 0.00 am to 1 am, of 4–6, strong explosive activity with new lava flow. At 3,30 am, lava 3–6, two strong earthquakes with collapse of the conelet fountains 300 m high lasting half an hour. Increase at 6:30 am with new lava and ejection of scoriae inclined to W. Since 8 am, lava flow, outside Somma caldera, toward Terzigno. On 13-3, collapse of the conelet; 14-3, moderate explosive 18 March at 4.30 pm, lava flow to N; at 11.00 pm-outflow to activity; 18-new collapse of conelet; W. New lava flow to SW at 11.00 am of 19-3. On 21 March at 5 pm- Lava fountains: I fountain 17.15–17.35, II fountain 20.10–20.30, III fountain 22.00–22.25; 22–3 IV fountain 01.40–02.10, V fountain 03.45–04.03, VI fountain 05.35– 06.15, VII fountain 06.30–07.05, VIII fountain, 07.31–17.50. At 12.48 pm, the lava fountain turns ashy with a sustained column 6 ed 7 km asl high, small glowing avalanches
References Alfano, G.B., Friedlaender, I., 1929. La storia del Vesuvio illustrata da documenti coevi. Karl Hohn Verlag, Ulm. 69 pp. Arrighi, S., Principe, C., Rosi, M., 2001. Violent strombolian and subplinian eruptions at Vesuvius during post-1631 activity. Bull. Volcanol. 63, 126–150. Auger, E., Gasparini, P., Virieux, J., Zollo, A., 2001. Seismic evidence of an extended magmatic sill under the Mt. Vesuvius. Science 294, 1510–1512. Barberi, F., Leoni, L., 1980. Metamorphic carbonate ejecta from Vesuvius plinian eruptions: evidence of the occurrence of shallow magma chambers. Bull. Volcanol. 43-1, 107–120. Bertagnini, A., Cioni, R., Rosi, M., Guidoboni, P., Neri, A., 2006. Eruption early warning at Vesuvius: The A.D. 1631 lesson. Geophys. Res. Lett. 33, L18317. doi:10.1029/2006GL027297. Bianco, F., Castellano, M., Milano, G., Ventura, G., Vilardo, G., 1998. The Somma–Vesuvius stress field: seismological and mesostructural data. J. Volcanol. Geotherm. Res. 82, 199–218. Bianco, F., Castellano, M., Milano, G., Ventura, G., Vilardo, G., Ferrucci, F., Gresta, S., 1999. The seismic crisis at Vesuvius during 1995 and 1996. Phys. Chem. Earth 24, 977–983. Borgia, A., Tizzani, P., Solaro, G., Manzo, M., Casu, F., Luongo, G., Pepe, A., Berardino, P., Fornaro, G., Sansosti, E., Ricciardi, G.P., Fusi, N., Di Donna, G., Lanari, R., 2005. Volcanic spreading of Vesuvius, a new paradigm for interpreting its volcanic activity. Geophys. Res. Lett. 32, L03303. doi:10.1029/2004GL022155. Braccini, G.C., 1632. Dell'Incendio fattosi al Vesuvio a' XVI Dicembre 1631, e delle sue cause ed effetti, Roncaglioli, Napoli. 224 pp. Breislak, S., Winspeare, A., 1794. Memoria sull'eruzione del Vesuvio accaduta la sera de' 15 giugno 1794. Napoli, p. 87. Carta, S., Figari, R., Sartoris, G., Sassi, E., Scandone, R., 1981. A statistical model of Vesuvius and its volcanological implication. Bull. Volcanol. 44-2, 129–151. Cassano, E., La, Torre, P., 1987. Geophysics. In: Santacroce, R. (Ed.), Somma Vesuvius. Quaderni de ‘La Ricerca Scientifica, 114/8. CNR, Rome, pp. 175–196. Cubellis, E., Marturano, A., April 2006. Analysis of historical and present earthquakes at Vesuvius for seismic hazard evaluation. EGU General Assembly 2006, EGU06-A-08131, 2–7. Austria, Vienna.
Cubellis, E., Luongo, G., Marturano, A., 2007. Seismic hazard assessment at Mt. Vesuvius: maximum expected magnitude. J. Volcanol. Geoth. Res. 162, 139–148. Delibrias, G., Di Paola, G.M., Rosi, M., Santacroce, R., 1979. La storia del complesso eruttivo Somma–Vesuvio ricostruita dalle successioni piroclastiche del Monte Somma. Rend. Soc. Ital. Mineral. Petrol. 35, 411–438. De Natale, G., Capuano, P., Troise, C., Zollo, A., 1998. Seismicity at Somma– Vesuvius and its implications for the 3D tomography of the volcano. J. Volcanol. Geoth. Res. 82, 175–197. De Natale, G., Kuznetzov, I., Kronrod, T., Peresan, A., Sarao’, A., Troise, C., Panza, G.F., 2004. Three Decades of seismic activity at Mt Vesuvius: 1972– 2004. Pure Appl. Geophys. 161, 123–144. De Natale, G., Troise, C., Pingue, F., Mastrolorenzo, G., Pappalardo, L., 2006. The Somma–Vesuvius volcano (Southern Italy): structure, dynamics and hazard evaluation. Ea. Sci. Rev. 74, 73–111. Finetti, I., Morelli, C., 1974. Esplorazione sismica a riflessione nei golfi di Napoli e Pozzuoli. Boll Geof. Teor. Appl. 16, 175–222. Fulignati, P., Marianelli, P., 2007. Tracing volatile exsolution within the 472 AD “Pollena” magma chamber of Vesuvius (Italy) from melt inclusion investigation. J. Volcanol. Geoth. Res. 161, 289–302. Guidoboni, E., Boschi, E., 2006. Vesuvius before the 1631. Eruption EOS 87-40, 417,423. Imbò, G., 1949. L'attività eruttiva vesuviana e relative osservazioni nel corso dell'intervallo 1906–1944 ed in particolare del parossismo del Marzo 1944. Ann. Oss. Ves. Ser. V. 185–380 (volume unico). Imbò, G., Casertano, L., Bonasia, V., 1964a. Attivita’ Vesuviana ne.g.,li ultimi anni dell’attuale riposo. Ann. Oss. Ves. Ser. VI (6), 189–204. Imbò, G., Casertano, L., Bonasia, V., 1964b. Considerazioni sismo-gravimetriche sulle manifestazioni vesuviane del maggio 1964. Ann. Oss. Ves. Ser. VI (6), 177–188. Lomax, A., Zollo, A., Capuano, P., Virieux, J., 2001. Precise, absolute earthquake location under Somma–Vesuvius volcano using a new 3D velocity model. Geophys. J. Int. 146, 313–331. Malladra, A., 1923. Sul graduale riempimento del cratere del Vesuvio. Atti VIII Congresso Geografico Italiano, II, pp. 3–11. Marianelli, P., Sbrana, A., Metrich, N., Cecchetti, A., 2005. The deep feeding system of Vesuvius involved in recent violent strombolian eruptions. Geoph. Res. Lett. 32. doi:10.1029/2004GL021667.
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Marzocchi, W., Sandri, L., Gasparini, P., Newhall, C., Boschi, E., 2004. Quantifying probabilities of volcanic events: the example of volcanic hazard at Mount Vesuvius. J. Geophys. Res. 109, B11201. doi:10.1029/2004JB003155. Mercalli, G., 1905. Notizie Vesuviane. Boll. Soc. Sismol. Ital. XI pp. 24–44. Mercalli, G., 1913. Il Riposo Attuale del Vesuvio. Rend. Accad. Sci. Fis. Mat. 3, 1–3 Napoli. Morgan, D.J., Blake, S., Rogers, N.W., De Vivo, B., Rolandi, G., Davidson, J.P., 2006. Magma chamber recharge in the century prior to the eruption of AD 79. Geology 34, 845–848. doi:10.1130/G22604.1. Nazzaro, A., 1997. Il Vesuvio: Storia Eruttiva e Teorie Vulcanologiche. Liguori Editore Napoli. 374 pp. Newhall, C.G., Albano, S., Matsumoto, N., Sandoval, T., 2001. Roles of groundwater in volcanic unrest. J. Geol. Soc. Phil. 56, 69–82. Palmieri, L., 1862. Cronache del Vesuvio dal 1852 al 1862. Ann. R. Oss. Vesuviano, Anno II, 1–19. Principe, C., Tanguy, J.C., Arrighi, S., Paiotti, A., Le Goff, M., Zoppi, U., 2004. Chronology of Vesuvius' activity from AD 79 to 1631 based on archeomagnetism of lavas and historical sources. Bull. Volcanol. 66, 703–724. Russo, F., 2002. L’eruzione del Vesuvio del 1794: Cronaca dell’Eruzione e Modificazioni Geomorfologiche del Paesaggio Vesuviano, Ottaviano, p. 41. Santacroce, R., 1987. Somma–Vesuvius. CNR Quaderni della Ricerca Scientifica 114 (8), 251.
Scandone, R., Giacomelli, L., Gasparini, P., 1993. Mount Vesuvius: 2000 years of volcanological observations. J. Volcanol. Geoth. Res. 58, 5–25. Scandone, R., Cashman, K., Malone, S.D., 2007. Magma supply, magma ascent and the style of volcanic eruptions. Ea. Pl.. Sci. Lett. 253, 513–529. doi:10.1016/j.epsl.2006.11.016. Scandone, R., Giacomelli, L., Fattori Speranza, F., in press, Persistent Activity and Violent strombolian eruptions at Vesuvius between 1631 and 1944, J. Volcanol. Geoth. Res. doi: 10.1016/j.jvolgeores.2007.09.014. Sorrentino, I., 1734. Istoria del Monte Vesuvio. Giuseppe Severini, Napoli. 224 pp. Stothers, R.B., Rampino, M.R., 1983. Volcanic eruptions in the Mediterranean before AD 630, from written and archeological sources. J. Geophys. Res. 88, 6357–6371. Zollo, A., Gasparini, P., Virieux, J., Le Meur, H., de Natale, G., Biella, G., Boschi, E., Capuano, P., de Franco, R., dell’Aversana, P., de Matteis, R., Guerra, I., Iannaccone, G., Mirabile, L., Vilardo, G., 1996. Seismic evidence for a low-velocity zone in the upper crust beneath Mount Vesuvius. Science 274, 592–594. Zollo, A., Gasparini, P., Virieux, J., Biella, G., Boschi, E., Capuano, P., de Franco, R., Dell’Aversana, P., de Matteis, R., De Natale, G., Iannaccone, G., Guerra, I., Le Meur, H., Mirabile, L., 1998. An image of Mount Vesuvius obtained by 2D seismic tomography. J. Volcanol. Geotherm. Res. 82, 161–174.
Journal of Volcanology and Geothermal Research 171 (2008) 191 – 200 www.elsevier.com/locate/jvolgeores
Research paper
Precursors of eruptions at Vesuvius (Italy) Roberto Scandone ⁎, Lisetta Giacomelli Dipartimento di Fisica, Università Roma Tre, Via Vasca Navale 84, 00146, Roma, Italy Received 1 August 2007; accepted 14 November 2007 Available online 4 December 2007
Abstract The historical record of activity of Mount Vesuvius is uncommonly long and may serve as a guide to understand precursors before the outbreak of new activity. Reposes of different lengths have been observed in the past, with long ones preceding violent explosive eruptions. Eruptions occurring during periods of permanent activity have been preceded by possible deformation of the volcanic edifice and by short duration, earthquake swarms. Otherwise they have occurred without any reported precursors. The renewal of activity after long periods, like the current one, has been preceded by unrest lasting years to weeks, as a new eruption would require connection to the surface of a reservoir at depth ranging between 6 and 4 km. Since 1944, episodic seismic swarms, have occurred with a frequency similar to that of the violent strombolian eruptions during the last period of permanent activity; they are interpreted as intrusions and arrest of magma batches into a reservoir at the same depth of that feeding past sub-plinian eruptions. © 2007 Elsevier B.V. All rights reserved. Keywords: Vesuvius; precursors; eruption
1. Introduction Mount Vesuvius is located in Southern Italy near the city of Naples in an area with one of the highest densities of population in the world. The volcano is built at the crossing of NW–SE, and NE–SW trending, oblique-slip faults, and E–W trending normal faults (Fig. 1) (Bianco et al., 1998). The NE–SW trend is also evidenced by the Differential SAR Interferometry (DInSAR), (Borgia et al 2005), showing that the SE sector is moving to the E relatively to the NW sector, and by seismic reflection profiles in the bay of Naples (Finetti and Morelli, 1974). Bouguer gravimetric anomalies of the volcano provide evidence of a shallow denser structure without very deep roots (Cassano and La Torre, 1987). A prominent high–density core has been also identified by seismic tomography (Zollo et al., 1996) concentric with the caldera structure. Seismic tomography also shows an extended low velocity layer at about 8–10 km
⁎ Corresponding author. E-mail address: [email protected] (R. Scandone). 0377-0273/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jvolgeores.2007.11.018
depth, interpreted as the top of a magma reservoir, having a surface area of at least 400 km2 (Auger et al., 2001). The last eruption of Vesuvius occurred in 1944, and, since then, only episodic swarms of earthquakes have characterized its state of activity. A repose of such length is unusual within the record of activity since 1631 (Carta et al., 1981), but is not unusual in the longer historical and geological record. A long period of quiescence, lasting possibly since 1139AD (uncertain eruptions are reported in 1306, Principe et al., 2004, in 1500 and 1571, Guidoboni and Boschi, 2006), ended on the 16th of December 1631 with a sub-plinian eruption. Also before the eruption of 79 AD there was a long period of quiescence lasting since many centuries, if we consider as a false event the 216 BC eruption quoted by Stothers and Rampino (1983). A few Greek and Roman scholars (Strabo, Diodorus Siculus, Vitruvius, Vergil) recognized the volcanic nature of the mountain before the eruption of 79 AD without reporting historical eruptions. Long periods of quiescence at Vesuvius ended with explosive eruptions (Plinian or sub-plinian) (Santacroce, 1987) as well as with effusive or mildly explosive eruptions (Arrighi et al., 2001). Currently it has been suggested, that the most
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Fig. 1. Simplified structural map of Vesuvius (modified after Bianco et al., 1998).
likely event in case of renewal of activity is a VEI = 3 eruption; more violent eruptions have a lesser probability (Scandone et al., 1993; Marzocchi et al., 2004). Given the high number of people (more than 500,000) living in the immediate threat of even a small sized eruption, it is of paramount importance to understand the nature of phenomena that may precede the outbreak of activity and provide a sufficient time to adopt precautionary measures of evacuation. In order to provide such data we revised the historical and recent reports of activity of Vesuvius to identify precursory signs and the possible style of a future activity. 2. Precursors after long repose periods The presence of extensive palesols below the deposits of plinian and sub-plinian eruptions at Vesuvius suggests long periods of quiescence before these events (Delibrias et al., 1979; Principe et al., 2004). One such event was the eruption of 79 AD, which destroyed the cities of Pompeii, Herculaneum and Stabiae. The poet Silius Italicus reports evidence for an eruption of Vesuvius in the poem “Punica”, in coincidence with the defeat of Romans by Hannibal at Cannae (216 BC). It is however doubtful that such an eruption may have occurred without any other reports from contemporary sources of the period, who describe many battles fought in the following years at the foot of
the volcano such as those at Nolae and Nuceria. It is more likely that Silius Italicus, who lived in Naples in his late years after the eruption of 79 AD, may have actually seen the eruption and might be willing to give a poetic account of it in his epic poem. Diodorus Siculus (80–20 BC) reports that the Campanian plain was called “Phlegrean (“fiery”) from the mountain which of old spouted forth a huge fire as Aetna did in Sicily; at this time, however, the mountain is called Vesuvius and shows many signs of the fire which once raged in those ancients times.” Collectively all Roman and Greek authors do not provide any strong evidence that during their time (since VIII–VII century BC) there was any eruption of Vesuvius; instead they report several eruptions on Ischia island where archeological and geological studies confirm the historical reports. The most recognized naturalist in imperial time: Pliny the Elder did not include Vesuvius in any list of volcanoes, so we may confidently assume that the volcano had been quiescent since several centuries before the 79 AD eruption that killed him. The first signs of unrest occurred a few years before the eruption. Seneca reports that a major earthquake occurred on 5 February of 62 AD. The earthquake flattened Pompeii, made great ruins in Herculaneum, and caused minor damage in Nuceria and Naples (Fig. 2). The aftershocks lasted for several days until they became milder “but still caused great damage”. Cubellis and Marturano (2006) suggest that the earthquake
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Fig. 2. Basrelief found at Pompeii remembering the earthquake of 62 AD (Naples, National Museum).
occurred below Vesuvius and had a magnitude of 5.1–5.4. Cubellis et al. (2006, 2007) suggest that there was also another major earthquake in 64 AD, which caused damages in the Vesuvian area, and scared Emperor Nero during a performance in Naples theatre. The psychological shock caused by the earthquakes to local inhabitants was so serious that it compelled Seneca to write his treatise on Natural Phenomena (Naturales Questiones) to support his friend Lucilius living in the area. The results may have proven more successful than desirable. Immediately before the eruption of 79 AD, earthquakes occurred for some time, but were disregarded by local inhabitants because of their familiarity with the phenomenon. As the Younger Pliny testified, “for several days before (the eruption) the earth had been shaken, but this fact did not cause fear because this was a feature commonly observed in Campania”. Extensive repair works were underway in many houses at Pompeii and Oplonti, and Boscoreale before the occurrence of the eruption (Fig. 3). We regard this as an evidence of the intensive seismic shaking due to a prolonged period of seismicity. A long period of repose, lasting at least 150 years, preceded the sub-plinian eruption of 1631. Several months before the beginning of the eruption, people near the volcano felt some earthquakes (Braccini, 1632). They were not particularly scared because earthquakes from the nearby Apennine chain were often felt in the area (a large one had occurred four years before in Apulia, in 1627). Incidentally, Braccini (1632) uses the same words as Pliny the Younger, for the attitude of the inhabitants to prolonged periods of earthquake swarms. The seismic activity became more severe in the few days before the eruption. According to Braccini (1632) the signs of an impending eruption were so evident that people should not have disregarded them but “Perituri non recipunt consilia” — (“those that are to die, do not accept advice”). Bertagnini et al. (2006) provided a detailed reconstruction of the precursors basing on contemporary chronicles. They report that rumbles, landslides in the crater and on the flanks of Somma were observed from September 1631. Since the end of November, muddy well water and salinity variations were observed in the springs at the foot of Vesuvius. Deformation and fracturing on the flank of the volcano occurred some days before the eruption. Braccini (1632) reports that at least 15 days before the eruption, the crater had been filled (possibly by landslides or piston-like uplift of the crater
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floor) and could be crossed from one side to the other. On 11 December, the vegetation inside the crater was burnt and there was a strong sulfur smell. A continuous rumbling was felt by the inhabitants of Torre del Greco, Resina (Ercolano) and S. Sebastiano since 10 December. Starting from the night before the eruption, a significant increase of seismic activity occurred, culminated, few hours later with the onset of the eruption (Bertagnini et al., 2006). Cubellis et al. (2006) suggest that the maximum magnitude of the earthquake swarm was 4.2. This activity culminated on the morning of 16 December 1631 with the opening of a new vent on the SW flank of the volcano and the development of a devastating explosive eruption, which destroyed all the villages at the foot of the volcano and caused 4000 deaths. The eruption left such an impression on contemporaries that the Spanish Vice—King of Naples, Emmanuele Fonseca, ordered the engraving of a memorial stone with a warning to posterity which is still now compelling: “…Sooner or later the mountains will burn again, but before, will moan, tremble and shake the ground, and smoke and flames and lightning will flash across the sky, then sounds and thunders will drive the inhabitants away...”. 3. Precursors during persistent activity The eruption of 1631 started a period of persistent activity, punctuated by violent strombolian eruptions that lasted, with
Fig. 3. Repairs works made in Pompeii, and nearby villages immediately before the burial of the town during the 79 AD eruption of Vesuvius, provide evidence of an intense seismic swarm preceding the eruption by a few days, as testified by Pliny the Younger. The arrow show a pole sustaining the lintel of a door of a country “Villa” at the foot of Vesuvius (Boscoreale) buried during the eruption.
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Fig. 4. Frequency of different precursor types observed during the period 1631– 1944.
a few breaks, for more than three centuries until 1944. The survivors of the eruption of 1631 re-established new settlements at the base of the volcano, on the same places destroyed by pyroclastic flows and lahars and became accustomed to its milder activity. A few individuals (mostly belonging to the ecclesiastic or noble classes) started to maintain detailed chronicles of its activity and to report the events, recording also subtle changes, precursory of some notable eruptions. These signs included abnormal seismic activity, variation in the depth and state of the water table, retreat of the coastal line, and failures of the conelet built inside the cone. We report in the Appendix, in Table A1, a summary of all these precursors extracted from an accurate analysis of contemporary sources. The results are summarized in Fig. 4. The most frequent precursor, observed in the 70% of all the reported cases (31), is the occurrence of seismicity; the second most observed precursor is the collapse of the conelet inside the crater possibly due to extensional phenomena preceding the magma ascent. The 1929 and 1944 eruptions were the only ones monitored with a seismograph (Imbò, 1949). The peculiar phenomenon,
that preceded by a few days the eruption of 1944, was the collapse of the conelet built inside the crater during the persistent activity of the preceding years. The collapse occurred on the 13th of March 1944, and was accompanied by a sudden drop, with respect to the value of the previous days, in the amplitude of harmonic tremor (Fig. 5). The emission of a lava flow on the 18th of March was accompanied by the increase in the amplitude of tremor. The collapse of the conelet and the drop in the amplitude of tremor were interpreted by Imbò (1949) as a drop in the height of the magma column. A closer analysis of the historic records indicates that other phenomena, like changes of the water table and sea retreat, probably related to deformation of the volcanic edifice, have commonly been observed from days to weeks before the eruptions. The variation of the level of water table has been observed also on other volcanoes either before eruptions or periods of unrest (Newhall et al., 2001). Earthquakes and collapse of the conelet, built inside the summit crater, were generally observed mostly in the few days preceding the eruption. It must be recalled that the reported earthquakes refer only to those felt by the inhabitants of the Vesuvian area, which, basing on current instrumental records, must have a magnitude higher than 2.0. A magnitude 3.5 is widely felt all over the Vesuvian area, and a magnitude 4.5 can cause slight damages in Naples (Cubellis et al., 2007). The decrease in the level of the water table is commonly reported in the areas nearby the villages of Resina (present Ercolano) and Torre del Greco (e.g. Alfano and Friedlander, 1929; Palmieri, 1862). In the same area were also observed retreats of the sea and, in one case (1861), a ground uplift of 110 cm (Palmieri, 1862). The three eccentric eruptions of 1760, 1794, and 1861 were all preceded by a seismic crisis lasting three days. The 1760 eruption occurred during a period of persistent activity with strombolian explosion at the summit crater. At the end of November 1760, there was a decrease of the intensity of strombolian activity, with a subsequent sudden increase at the beginning of December. On 12 December strong explosion were heard also in Naples (13 km from the summit
Fig. 5. Amplitude of the tremor measured by an Omori–Alfani seismograph operating at the Vesuvius Observatory since 1914. The amplitude has a sudden drop in coincidence with the collapse of the conelet built inside the cone.
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cone). At 5 pm of 20 December, many small earthquakes were felt in the villages at the foot of the volcano, and at 7:30 pm of 23 December, a strong shock and a continuous tremor accompanied the opening of an eruptive fracture on the south flank at about one and half mile from the main road along the coast. Again at 8:15 pm, a new strong shock accompanied the opening of another vent at a lower altitude. The eruption of 1794 was preceded by a period of quiescence lasting since at least 9 months (Russo, 2002). A decrease in the level of the water table occurred weeks to days before the eruption, and rumblings were heard in the last 2–3 days before the eruption (Russo, 2002). Intense seismicity was felt only 3 days before the eruption with an earthquake strongly felt over a wide area especially to the NE of the volcano and in the nearby Apennines. The earthquake occurred on 12 June 1794, at 21:15 and was felt as an undulatory movement and did not cause any damages in the towns surrounding the volcano, so we infer that it may have been relatively deep, or of tectonic origin in the Apennines. Other shocks were felt at 01:00 and 08:00 of the 13th (Breislak and Winspeare, 1794). The inhabitants of Torre del Greco felt many earthquakes between the 12th and the15th of June, along with a mild continuous shaking of the ground. The people living in Naples felt only the first earthquake occurred on the 12th (Breislak and Winspeare, 1794). The eruption was preceded by a two-hours long, intense, seismic swarm at 21h, on the15th of June, immediately before the outbreak of a fracture, which opened on the lower flank of the cone immediately above Torre del Greco. A lava
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flow issued from the fracture and, after a few hours, invaded and completely destroyed the town (Fig. 6). The eruption of 1861 followed a 2 years long eruption began in 1858 and ended on April 1861. This was the first one monitored with a seismograph built by G. Palmieri, Director of the newly built (1841) Vesuvius Observatory (Palmieri, 1862). An uplift of the ground of 110 cm preceded the eruption, and on 5 December 1861 there was a strong felt earthquake and the spilling of water wells in Torre del Greco. The water had a temperature of 38°C and was rich in CO2. During 5 and 6 December, there were many light shocks recorded by the Palmieri seismograph and on 7, they were also felt in the villages at the base of Vesuvius. At 9:00 am of 8 December, there was the intensification of the earthquake swarm and of rumblings. At 16:00, the opening of lateral vents at an altitude of 290m asl and a set of SW–NE trending fractures through Torre del Greco caused the destruction of many buildings. A small lava flow reached the outskirts of the town (Palmieri, 1862). Unfortunately, after this eruption there are no more reports of water well anomalies, possibly because of the increasing major attention paid to scientific instruments deployed at Vesuvius Observatory. Not all the eruptions, occurred during this period, were preceded by significant seismic activity and not all eruptions have been preceded by other observed precursory phenomena. Actually, many of them have been practically silent. Mercalli (1905) notes that many paroxisms are actually preceded by long periods of reduced activity. However, several others (e.g. 1872) have been preceded by periods of increased strombolian activity. For example the eruption of 19 October 1767 was preceded by an increased strombolian activity that caused a marked increase in the height of the scoria cone built within the summit crater. Often, reawakening after the short periods of repose between 1631–1944 occurred with mild activity like in 1875 or 1913. The 7 years long repose after the eruption of 1906 ended in 1913 with only a few recorded earthquakes (Mercalli, 1913) and the formation of a collapse pit inside the crater left by the previous eruption; these phenomena were followed by a quiet emission of lava inside the collapse pit (Malladra, 1923). 4. Discussion and conclusions
Fig. 6. The initial opening of a lateral fracture on the SW flank of Vesuvius during the 1794 eruption (by Saverio della Gatta, private collection).
Marianelli et al. (2005), Scandone et al. (in press) suggest that the permanent activity of Vesuvius between 1631 and 1944 was fed by a magma accumulating at shallow depth within the volcanic edifice. The violent strombolian eruptions were caused by episodic, multiple arrivals of discrete batches of magma rising faster and not degassing during the ascent (Scandone et al., 2007). The rapidly ascending magma pushed up the liquid residing in the shallow reservoir, caused fracturing of the upper volcanic edifice, and eventually reached the surface with its full complement of volatiles, producing fast lava flows and kilometer-high lava fountains. The precursors observed during this period signal the complex interaction between the shallow residing magma responsible for the persistent activity and the arrival of the fast multiple ascending batches, which cannot be accommodated in the
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shallow plumbing system. The water table of a volcano can be regarded as a proxy of a dilatometer as it is strongly related with strain changes within the volcanic edifice (Newhall et al., 2001). During the period 1631–1944, all the anomalies of the water table (but the one in 1861) report a drop in the level of water wells in areas near the villages of Torre del Greco and Ercolano. This area is a on a NE–SW trending, normal fault crossing Vesuvius (Fig. 1) (Finetti and Morelli, 1974; Bianco et al., 1998). The lateral vents of the eruptions of 1631, 1794 and 1861, as well as pre-1631 lateral vents (Sorrentino, 1734) opened along this fault which is believed to be the main fracture feeding the activity of the volcano (Scandone et al., in press). We suggest that the intrusion of magma batches at shallow depth may cause a dilation perpendicular to the direction of this fault with creation of voids and drop of the level of water table. Multiple intrusions may eventually cause the fracturing of the flank of the volcano, signaled by the precursor seismicity with the sudden drop of the magma column residing in the top of the edifice and the collapse of the conelet. Alternatively, such phenomena may be interpreted as related to an external tectonic trigger. In this case, dilational strain accumulation on the NE– SW fault, signaled by water well changes, causes the arrival of fast ascending magma batches, which fracture the upper flank of the volcano. This pattern ended in 1944 because of the progressive cooling of the magma residing in the shallower part of the volcano (Scandone et. al, in press). Such circumstance is also supported by the seismic tomography evidencing a region with an anomalous high-velocity of propagation of seismic waves, which starts from about 400m below the crater and extends down to at least 3000m. The highest velocities 3.8–4.0km/s are observed about 1500–2000m below the surface (Zollo et al 1996, 1998; De Natale et al., 1998). These authors interpreted the anomaly as due to a plexus of solidified dykes. The cooling of magma residing in the shallow reservoir is responsible for the present period of quiescence longer than any observed between 1631 and 1944. Such repose has a length smaller than that before 1631, but comparable with other reposes occurred during the Middle Age (Alfano and Friedlander, 1929). Renewal of activity after long quiescence periods has occurred often with violent sub-plinian or plinian eruptions fed by magma accumulated in a shallow reservoir at a depth of the order of 3–6 km (Barberi and Leoni, 1980; Santacroce, 1987). During the present repose, significant thermal anomalies were observed from 1952 to 1954 with an increase in the temperature of fumaroles within the crater from 350 to 600°C (Imbò et al., 1964a), and again on 11 May, 1964, with a widely felt shock (Imax = 5 Mercalli Scale at the foot of Vesuvius) (Imbò et al., 1964b). Since then, the temperature of the fumaroles has decreased (Nazzaro, 1997). Major seismic crises occurred in 1978–80, when there was a swarm of moderate earthquakes (M b 3). The most significant earthquake since 1964 occurred in 1999 with Md = 3.6, accompanied by a relatively small number of earthquakes with Md N 1.8 (De Natale et al., 2006). Since 1985–86, there has been a progressive decrease of the b-value of the earthquakes, an alternating sequence of seismic quiescence and activity, and an increase in the observed earthquake
magnitude (De Natale et al., 2004, Bianco et al., 1999). The source mechanisms of the major earthquakes are compatible with isotropic components that indicate volumetric expansion (De Natale et al., 2004). The average depth of the earthquakes is comprised between 2 and 6 km (De Natale et al., 1998; Lomax et al., 2001; De Natale et al., 2006). The recurrence rate of seismic swarms or thermal anomalies in the past 50 yr is = 0.14yr− 1, similar to the recurrence rate of paroxistic eruptions evaluated until 1944 (0.13yr− 1) (Scandone et al., in press). We infer that the episodic occurrence of seismic crises is suggestive of discrete episodes of magma intrusions in the same zone that fed the sub-plinian eruptions in the past (Fulignati and Marianelli, 2007). Seismicity occurs when the added, magma volume cannot be accommodated by aseismic compression of surrounding rocks, and spreading of the volcano (Borgia et al., 2005). We suggest that a catastrophic failure of this reservoir and the migration of magma to the surface is likely to be accompanied by a significant seismicity increase in the zone above it: namely in the top 2–3 km of the volcanic structure presently not greatly affected by seismicity. The intensity and magnitude of a future eruption depend on the ratio between the cooling rate of ascending batches and their feeding rate into the shallow reservoir. It is currently not possible to estimate the duration of possible future precursors basing only on the past history of the volcano. The earthquakes before the eruption of 79 AD lasted for decades (Cubellis et al., 2006, 2007). This circumstance is also confirmed by the timing of multiple intrusions into the magma chamber that fed the eruption. Morgan et al. (2006) ascribe the resorption of Ba-poor crystal rims of the sanidine in the products of the eruption, and re-growth of Ba-rich rims to the intrusions of hot magma batches in the century preceding the eruption with a significant magma recharge 20 yr before 79 AD, close to the 62 AD earthquake reported by classical authors. Such extended periods of anomalies may cause a major problem in the planning of measures for the reduction of the risk, which could require mass evacuation of the areas subject to the eruption treat. Volcanic unrest at quiescent volcanoes may not be immediately followed by eruption, but may represent a build up to critical conditions. There is no certainty that the build up follows a linear, or a time predictable trend as it may be related, as the past history shows, to episodic pulses into a magma chamber. Currently there is no rule for establishing a critical threshold, unless gathering a more detailed knowledge of the stress state inside the volcanic edifice and an average magma supply rate into it. The replies to these questions may require the drilling of exploratory wells into the roots of the volcano, which in terms of cost-benefit analysis, may not represent an impossible task in the near future. Acknowledgements J.C. Tanguy and Chris Newhall made useful comments to an early draft of this manuscript. We acknowledge partial financial support from INGV and Dipartimento Protezione Civile Nazionale of Italy, and MIUR-Prin Project 2005 (Risalita dei Magmi e Dinamica delle Eruzioni).
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Appendix A Table A1 Precursors of eruptions and renewals of activity in the period 1631–1944 YEAR
Observed phenomena
Notes
Eruption
1631
1660
Seismicity, deformation, and landslides at crater, fumaroles increase Earthquakes
In the early morning of the 16th December opening of a fracture on SW flank of volcano and beginning of explosive eruption Explosive eruption on 3 July 1660
1682
Earthquakes
1694
Earthquakes; Collapse of Conelet
1696
Earthquakes
1697
Earthquakes
Few days before the eruption are reported earthquakes and rumblings felt in the villages around Vesuvius. Strong seismic crisis in the night preceding the eruption (see details in the text) An earthquake swarm felt at Ottaviano on the 3rd of July hours before the start of the eruption Since beginning of August: earthquakes and rumbling felt at Torre del Greco Since March: seismicity felt in Torre del Greco. On 12 March strong strombolian activity, explosions and earthquakes. On 5 April explosion and collapse of Conelet. Earthquakes and explosions since 31 July lasting till 4 August 1696. Earthquakes on 15 September
Explosive Eruption starts on 12 August, 1682 Lava flows begins on 13 April (lasts for 15 days)
Lava flows starts on 4 August (10 days)
Fracturing of the cone and lava flow on 19 September for 8 days 1698 Earthquakes, Rumbles On 14 May, the sea retreats 5 times along he coast of Torre del The lava flows starts on 25 May and last until 2 June. and sea retreat Greco. On 19 May, earthquakes and rumblings with stronger Explosive activity since 7 June. explosive activity. 1705–1706 Earthquakes Earthquakes felt between 19 January 1705 and 20 July 1706 Frequent explosions 1707 Earthquakes Since July, felt earthquakes and small lava outflows, Explosive activity and emission of a lava flow on 29 July. increasing on 28 July with the opening of a fracture on the Eruption ends 18–22 August SW flank 1723 Earthquakes, Water Since 18 March, decrease of water table in Torre del Greco Explosive activity at the crater between April, 20 and June 25, Table, Sea Retreat and sea retreat for three times. On 29 March, felt earthquakes. The eruption begins on 25 June with the emission of a lava Strong seismic activity on 30 June flow and strong explosive activity between 2 and 4 July (eruptive cloud like “a giant black pine tree” 1730 Sea Retreat, water table Intra-crateric activity since 27 February. Explosions since 2 Strong explosions on 24–25 March and collapse of crater on March and lava flow 17–23 March. On 23 March, sea retreat 25 March with strong explosions and the emission of a fast and decrease of level in water wells at Torre del Greco lava flow. Eruption ends on 1 April 1737 Water table, earthquakes Before eruption, decrease of water in wells at Somma. Water Eruption begins on 19 May. Strong explosions on 20 May with acidulous flavour and sulfur smelling. On 17 March felt with earthquakes that caused some collapses in Naples. On 21 earthquakes. Increase of strombolian activity and a giant May a fast lava flow from the flank of the volcano reached the eruption cloud on 15 May. After the eruption: Mofettes and sea coast and partially destroyed Torre del Greco for the first time since 1631 acid water in wells 1751 Earthquakes On 22 October an explosion felt in Ottaviano, on 23 October The eruption begins on 25 October with the fracturing of the at 5:30 pm, an earthquake felt in Naples SE flank of the cone 1756 Sea retreat On 23 June, sea retreat at Castellammare, and again on 9 On 12 August a lava flow toward Torre del Greco, and, on 12 August August, 2 lava flows toward Portici 1760 Earthquakes Felt earthquake swarm between 20 and 23 December. Beginning of eccentric eruption on 23 December at 19:30, on Stronger earthquakes since 17:30 of 23 December (see southern flank details in the text) 1770 Water table Lowering of water table at Volla and Torre del Greco before On 15 February 1770, explosive activity and felt tremor. On eruption. 16 March, earthquakes 16 March fracturing of the E flank of the cone and emission of lava. Again in April lava flows toward: Il Mauro and Boscoreale 1779 Earthquakes Felt earthquakes during July 1779. Increase of strombolian Explosions and eruptive column on 3 August. At the same activity at the end of July and small lava flows. Felt tremor at time opening of an eruptive fracture on the Nortern flank of 7:30 pm of 3 August the cone. On 5 August: explosion and collapse of the upper part of the crater. On the night between 7 and 8 August, violent explosive paroxism 1794 Earthquakes, water A tectonic earthquake on 12 June strongly felt at Avellino. On At 21 of 16 June, strong earthquake with an explosion and a table, rumbles 15 June numerous earthquakes felt around Vesuvius fracture on the SW flank of Vesuvius. A fracture propagates especially in the 2 h before the eruption. These quakes were upward and downward. Lava from the SW fracture invades hardly felt in Naples. Months to days before the eruption Torre del Greco, and reaches the sea. A lava flow issues from drying of water wells at Resina, Pompei; more evident since another fracture on the NE of the cone, and goes toward Torre 13 June. The water comes back after the eruption. Rumbles Annunziata and Il Mauro. On 17, increase of ash emission and collapse of the cone. Explosions until 18. On 20, strong heard since three days before the eruption earthquake and another collapse of Gran Cono. 1804 Earthquakes, water On 31 July, drying of water wells in Resina and Torre del Since 15–8, a lava flow toward Camaldoli, which stops on 30 table, sea retreat Greco and sea retreat between Torre del Greco and Torre September. On 2 September, the lava flow is at Monticelli. On Annunziata. On 11 August, felt earthquakes at Resina. 16, the lava stops at 0.3 mile from the Royal road. (continued on next page)
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Table A1 (continued ) YEAR
Observed phenomena
Notes
Eruption
1806
Earthquakes
Earthquakes felt at 2:30 am of 31 May
1813
Tremor and rumbles
Tremor and rumbles felt at 10 am of 25 December
1822
Water table, earthquakes Drying of water wells in Resina during September in coincidence with the opening of a new small vent within the crater, where there were already two other vents in strombolian activity. Increase of strombolian activity between 15 an 21 October. On 20–21 October, small earthquakes felt within 8 miles from the crater. At the same time there was a strong increase in the emission of black smoke. On 21 effusion of a lava flow from the summit crater.
1834
1850
Water table, earthquakes, collapse of conelet Water Table
Drying of water wells in the villages around Vesuvius. On 23 August, strong earthquake and collapse of the bottom of the crater. Decrease of water table observed on 23 January at Resina and Torre del Greco
1855
Rumbles
Rumbles heard during the night of 30 April in coincidence with the opening of a fracture on the N side of the cone. Variation in water table after eruption.
1861
Earthquakes, inflation
Strong earthquake felt on 5 December at 9 am. On 5 and 6 shocks recorded at Vesuvius Observatory, more numerous on the 7th when they are felt at Torre del Greco. At 8 am of 8 December, felt seismic activity at Torre del Greco increasing in intensity till 3 pm. On 8 December, inflation of the coast (1.1 m at Torre del Greco). Increase of water table during and after the eruption
1889
Collapse of conelet
Explosion and lava fountain at 2.30 am, on 31 May. Strong explosion at 3.15 pm. On 1–6,at 4 am, a lava flows to SW and W; one toward Camaldoli travels 3.5 miles in 1 h. Another flow reaches the sea near Torre del Greco. Eruptive cloud during the evening. New lava flow, 7 miles long, on 2–6. On 3, explosive activity. Activity until 9 June. At 2:00 pm of 25 December, explosion with eruptive cloud and lava toward Fosso Bianco; another flow toward Viulo; explosive activity and lava flows in January and February 1814. On 22 October (1 am), fire column on the crater, 2000 feet high; fracture of the cone to the E with a glowing avalanche. Outflow of lava at dawn, toward SW. After the lava emission, ash column toward SE. Decrease during the morning, and increase at 13 h, with tremors and a high column, at 16 h, strong explosion with emission of lava from E side. During the night, opening of new vents in the crater and on the flank toward Camaldoli; on 23 October (1 h), new explosions with an high eruptive column and strong tremor; collapse of part of the crater; 2 eruptive columns: white at W and dark at E. On 24 October, ash–fall; continuing activity with decreasing intensity until 16 November. Eruption column on 23 August, on 24 August, 4 vents on E flank of the crater; and, on 28–29 August, a lava flow toward Poggiomarino. Fracture along N side of the cone on 5–February; rapid lava flow into Atrio del Cavallo and then to E. On 7 and 9 February, increase of lava flow toward il Mauro and Poggiomarino. On the 9th, dense smoke from the crater with ash–fall on Torre Annunziata. Decrease of activity on 10 February; from 12 to 15, lapilli and, on 16 at 12,30, two strong explosions. Opening of vents on the N side of the cone with lava emission and mild strombolian activity. Lava flow into Atrio del Cavallo toward W to Vetrana, and Fosso del Faraone. During the night it reaches S. Sebastiano and Massa di Somma. New flows on 6–5 and 7–5 reach S. Sebastiano and Somma. On 8– 2, the lava flow arrives at 1/2 mile from Cercola. At 4 pm of 8 December, a fracture forms at 2 km above Torre del Greco at 290 m asl. The fracture trends ENE–SSW and extends into the sea.Conelets form since 4 pm in the higher part of the fracture with lava flow toward Resina and Torre del Greco. Smoke and mild explosions at the crater. Damages to the buildings of Torre del Greco because of the fracture; Earthquake on 11-1 and 16. On that day, at 8 am, boiling of the sea at 1500 m in front of Torre del Greco. Same phenomenon on 17-12, at 9 am. On 17-12, at 1 pm, eruption column at the crater, also during the night of 23-12, ash emission lasts until 31-12. Lava flows till September
1895
1903
1906
On 1 May collapse of conelet and opening of a fracture on the cone Earthquakes, collapse of On 3 July 1895 earthquakes accompanying the fracture of the On 3 July1895, fracturing of the WNW side of the cone with conelet cone. Collapse of the conelet on 3–4 July of 1895 new vents at 1185, 1100, 900 and 750 m asl. Lava flow from the lower vents into Fosso della Vetrana. Lava is emitted for all the year. On November 1895, the summit crater is 250 m deep. During September 1897, the depth of the crater decrease of 100 m due to landslides. At the beginning of July 1898, the crater is 60 m deep. The lava dome formed during this period is called Colle Umberto. Collapse of conelet On 22 August 1903 collapse of conelet and crater On 26 August, fracture on the Crater at WNW, explosion and lava flow onto Colle Umberto. On 27, fracture trending ENE at 800 m asl with lava flow. Collapse of 130 m of the crater with vulcanian explosions. Collapse of conelet, On April 4, black smoke and partial collapse of the cone (5,30 On 5–4, violent explosions and lava emission; on 6, at 8 am, earthquakes am); new vent at 1200 m on S flank of Gran Cono; lava; vent on SE flank of crater at 600 m asl; lava; intense activity at
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Table A1 (continued ) YEAR
Observed phenomena
1906
1911–1913 Collapse pit
1929
Earthquakes and collapse of conelet
1944
Collapse of conelet
Notes
Eruption
seismic activity; (14h) collapse of conelet; explosive activity the crater; (24: h) increase of seismicity. On 7 April, new vent from strombolian to vulcanian; on E flank, and lava toward Terzigno; outflow at the central crater; at 7 pm, explosions with incandescent ejecta up to 1–2 km above crater; 9 pm, explosion with fragmentary material; 11 pm, new lava emission; 8, at 030 am, strong explosions and earthquake; (2:30 am) violent earthquake with explosion and emission of ash, incandescent material and lithics. In July 1911, landslides within the crater. On 10 May 1913 a The volcano had been in a quiescent stage since the end of the collapse pit inside the crater with smoke issuing from it. eruption of 1906. Since July 1913, red glows in the crater and progressive lava filling of the collapse pit. Since 27 May, no activity. On 31-5, moderate strombolian On 3 June, rapid lava emission, out-flowing to E. Scoria activity until 2–6. At 3 pm of 2–6, frequent earthquakes. On ejection up to 300 m. Since 0.00 am to 1 am, of 4–6, strong explosive activity with new lava flow. At 3,30 am, lava 3–6, two strong earthquakes with collapse of the conelet fountains 300 m high lasting half an hour. Increase at 6:30 am with new lava and ejection of scoriae inclined to W. Since 8 am, lava flow, outside Somma caldera, toward Terzigno. On 13-3, collapse of the conelet; 14-3, moderate explosive 18 March at 4.30 pm, lava flow to N; at 11.00 pm-outflow to activity; 18-new collapse of conelet; W. New lava flow to SW at 11.00 am of 19-3. On 21 March at 5 pm- Lava fountains: I fountain 17.15–17.35, II fountain 20.10–20.30, III fountain 22.00–22.25; 22–3 IV fountain 01.40–02.10, V fountain 03.45–04.03, VI fountain 05.35– 06.15, VII fountain 06.30–07.05, VIII fountain, 07.31–17.50. At 12.48 pm, the lava fountain turns ashy with a sustained column 6 ed 7 km asl high, small glowing avalanches
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