Vesuvio volcano, Italy
NOTE: For a detailed description of the Vesuvian activity between 1631 and the mid-19th century, the best source is probably Roth's great 1857 monograph in which he cites lengthy from all contemporaneous reports available at his time. The following has much of the information gathered by him, but is organized according to Alfano & Friedlaender (1929), Santacroce (1987) and Scandone et al. (1993).
Activity between 1632 and 1694
Reports about the period between early 1632 and 1694 are sketchy and only an incomplete picture of the activity during this period can be drawn. Nonetheless it appears that Vesuvio was more or less constantly active during this time interval.
After the 1631 disaster, a new cone began building on the floor of the crater left by that eruption. The date of the onset of this activity is not known, but the earliest description was given by Athanasius Kircher who, in April 1638, climbed to the great crater and observed several boccas on the crater floor in Strombolian activity. A small cone had begun to form around the vents.
This kind of activity may have continued for the next years without causing much attraction among the population that was gradually returning to the sites of the 1631 destruction. Only on 28 Nov 1649 there was a somewhat larger eruption that caused ash and lapilli rains onto neighboring towns and panic among their residents. This increasd activity continued until late Jan or early Feb 1650.
Strombolian activity from the growing cinder cone within the 1631 crater was reported in 1652 and 1654. In 1659, the intracrateral cone had already assumed major proportions. However, the depth of the main crater was still about 400 m.
A major eruption occurred on 3-29 July 1660. A dark eruption column is said to have risen at least 4 km high and was driven to the SE. During the final stage of the eruption, white ash was erupted - a feature common in the late stages of all final (that is, sub-cycle-closing) Vesuvian eruptions. It was in this eruption that free twinned augite phenocrysts were ejected along with the ash, the cross-shaped objects falling from the sky causing much superstition among the population.
The crater was filled by a significant amount during the 1660 eruption.
Three intracrateral cones and lava flows were seen at the floor of the 1631 crater during a visit in 1670, but nothing is reported about the activity at that time. More intense Strombolian activity occurred on 26 March 1680. A somewhat larger eruption on 12-22 Aug 1682 ejected a large ash column, causing tephra falls and further filling of the 1631 crater. Lava issued from the active cone but did not overflow onto the outer slopes.
A similar but weaker eruption occurred on 3 Oct 1685. Vigorous Strombolian eruptions dropped incandescent bombs and spatter onto the upper portions of the active cone and caused some damage to vineyards.
The intracrateral cone was first seen to have grown higher than the rim of the 1631 crater in 1689 for the first time. During a period of increased activity in Dec of that year, the central cone reportedly grew by about 80 m. During 1690, activity was more or less continuous, and probably further growth of the central cone took place.
1694 eruption. The largest eruption since 1631 occurred in April 1694, when for the first time since the destruction of the old active cone, lava poured onto the outer slopes of the cone.
Earthquakes became more frequent and vigorous in March, and explosive activity in the summit crater began to increase on 5 April. Black ash fell around the volcano, and parts of the intracrateral cinder cone began to collapse.
On 13 April, a fissure opened at the base of the intracrateral cone, lava rapidly covered the floor of the 1631 crater, and soon overflowed towards San Giorgio a Cremano (towards WWNW) and Torre del Greco (SW flank). Efforts were made in Torre del Greco to divert the lava flow by building an artificial channel; how-ever, the lava apparently did not reach that far. That same day, a spectacular lava lake was observed in the W part of the crater basin (Roth 1858). Effusive activity lasted for about 2 weeks; after this, the intracrateral cone had gone. Vigorous ash emission around 20 April caused ash falls as far as Calabria; the last ash to be emitted was of whitish gray color.
NOTE: The activity of Vesuvio has been far better documented from the late 17th century on. It is apparent that the activity occurred in sub-cycles lasting several years to (rarely) a few decades and usually ending with powerful eruptions similar to that of 1694. Arnó et al., in Santacroce (1987), have recognized 18 sub-cycles (named "cycles of the recent activity" by them) between 1631 and 1944, 16 of them after 1694.
1696-1698 eruptive sub-cycle
After a repose period of 2 years and 3 months, Vesuvio became active again on 31 July 1696, and 4 days later, lava began to pour over the rim of the 1631 crater taking the same course as the 1694 lava. This effusive activity ended on 13 Aug, but resumed on 15-16 Sep. For the next year, the activity may have been normal Strombolian activity of the regrowing intracrateral cinder cone. On 18 Sep 1697, lava began to issue from 3 fractures at the base of the summit cinder cone which at the same time collapsed, and lava overflowed the SW crater rim towards Torre del Greco, remaining about 1 km from inhabited areas. Effusive activity stopped on 26 Sep. Minor lava outflow and increased explosive activity took place on 15-20 Nov, and again occasionally until Jan 1698.
1698 eruption. In mid-May of that year, unusual phenomena such as ground uplift at the coast near Napoli and rumbling noises preceded what was to become the final major eruption of the 1696-98 sub-cycle. Lava outflow took place, first within the 1631 crater basin on 19 May, and on the 25th, a voluminous lava flow overflowed the SW crater rim and began to advance towards Resina and Torre del Greco. It did, however, not reach populated areas and came to a standstill on 2 June.
From that day on the explosive activity of the volcano increased, and ash fell in Napoli on 7 June. For the next few days, voluminous ash emission occurred; on the 11th, the ash had a white color marking the end of the eruption. Only little ash emission was observed thereafter. Vesuvio fell into repose for about 2 or 3 years.
1700-1707 eruptive sub-cycle
Mild intracrateral activity may have begun as early as late 1700, but significant activity only started on 1 July 1701 when lava began to issue from the W base of the intracrateral cone and reportedly overflowed towards Ottaviano (that is, towards NE). More intense activity on 5 July produced a tall eruption column, and heavy ash and scoria falls occurred in Napoli, Ravello, Foggia, Somma, Palma, Lauro, Nola, and Marigliano, the coarser material falling closer to the volcano. Renewed lava emission occurred on 6-9 July. When all activity temporarily ended on the 15th, the summit cinder cone had been largely destroyed.
Only minor activity occurred during the next few years, persistent Strombolian activity gradually rebuilding the intracrateral cone that soon loomed over the rim of the remnants of the 1631 crater.
1707 eruption. The concluding eruption of this sub-cycle came on 20 July 1707 when lava effusion resumed within the summit crater basin that were accompanied by increasing explosive activity from the 26th on. Loud detonations damaged many windows and caused cracks in building walls on the 28th. Lava outflow onto the outer flanks reportedly began during the last days of July and followed the same course as the 1694 lava. Heavy tephra falls caused widespread damage in Torre Annunziata, Ottaviano, and several other towns. On the early afternoon of 2 Aug, ash rain caused darkness in Napoli.
During the next 16 days the activity gradually lost its vigor, and by 18 Aug, the eruption was over. Mudflows were caused by heavy rains on 2 and 24 Oct. Vesuvio remained quiet for the next 4.5 years.
1712-1737 eruptive sub-cycle
Minor explosive activity may have begun as early as Feb 1712, and lava effusion within the summit crater began on 26 April of that year. Lava slowly began to overflow onto the upper flanks while weak explosive activity occurred from the summit cinder cone. This slow effusive activity continued until 29 Sep. A similar period of low-rate effusive activity occurred 12 Ap-ril-25 May 1713. Still another period of essentially the same activity ensued in Jan 1714 and lasted until 30 June. During the last 10 days of this activity, lava came down to Boscotrecase but stopped just before having reached populated areas. At the same time, explosive summit crater activity increased and a tall eruption column rose from the volcano, with ash falling NE of the mountain.
Minor effusive activity may have occurred on 25 June 1715, and a brief period of stronger explosive activity took place on 10 April 1716.
From 6 June until Dec there was a period of slow lava emission onto the S and SW flanks, the lava reaching the E base of the Camaldoli parasitic cone. During this period, moderate Strombolian activity continued to build the summit cinder cone. Strombolian activity continued after the end of lava extrusion.
On 16 Sep 1718, lava began to be emitted again onto the SW and WSW flanks. This activity continued until 10 July 1719.
More intense explosive activity occurred on 7-29 July 1720, causing ash falls in Ottaviano. Lava effusion from the summit crater and fissures immediately below the summit took place on 1 May-15 June 1721. No unusual phenomena except the persistent weak summit Strombolian activity were observed until 26 June 1723 when lava issued from a fissure on the upper N flank and poured into the Valle dell'Inferno. This effusive activity ended on 1 July.
Little activity occurred during the next 14 months. On 14-20 Sep 1724, lava poured down the upper W, SW and S flanks. More vigorous lava effusion occurred on 12-29 Nov of the same year.
A period of prolonged lava effusion began on 10 Jan 1725 and lasted until 30 April 1726. Lava moved in the direction of Torre del Greco. During this activity, a couple of lava mounds or cupolas was built in the "Piano dell'antica montagna", on the W flank. Between 26 July 1727 and 29 July 1728, another lava cupola was built during low-rate lava effusion in the Piano delle Ginestre.
Continuing summit Strombolian activity had by 1730 built the summit cinder cone to great height, possibly for the first time since 1631 as high as the Somma. At this time, the 1631 crater was completely concealed by the growing cone.
After more than 2 years of relative quiet, Vesuvio had another slow lava effusion that was heralded by a brief lava overflow on 8 Jan 1733 and began in earnest on 27 April. The most intense lava emission occurred in June when the summit crater was filled with a lava lake. Most lava was then spilled onto the E flank, but in Nov and Dec, lava flows covered the S flank and advanced to near Torre del Greco. This period of effusive activity ended on 10 Jan 1734.
Minor lava effusion occurred in July 1735, and small-scale Strombolian activity from the summit cinder cone continued through April 1737.
1737 eruption. The 1712-37 eruptive sub-cycle came to an end with a powerful eruption that again brought disaster to the town of Torre del Greco, 106 years after its previous destruction.
Increased gaseous emissions from the summit crater were first observed on 14 May, and increased explosive activity began on the 16th; on that latter day a lava flow poured down the SE flank. At about 1500 on 20 May, a loud bang marked the opening of a fissure on the lower SW flank that emitted a minor lava flow; another flow poured over the first one at about 2200 but came to a standstill soon after. Then, at about midnight, a much larger lava flow issued from the fissure while explosive activity increased at the summit and a second flow poured from here onto the upper W flank. The main lava flow developed 2 minor branches that came down the Fosso Grande and Fosso Bianco; the main branch, however, was directed towards Torre del Greco and soon invaded the city. It surrounded two churches and destroyed a number of buildings but stopped on the 21st at a short distance (about 300 m) from the coast. The lava flow had reached a length of 7.5 km and was 50 m wide at its front; its total volume was estimated at 1.1 x 10^7 m^3.
While lava effusion had ended after this, explosive activity from the summit crater increased on 22 and 23 May, and heavy tephra falls occurred in Nola, Somma Vesuviana and Ottaviano. According to contemporary sources, max tephra thickness was about 1 m, causing many roofs to cave in. However, the eruption is not known to have caused any fatalities.
From 24 May, the eruption began to lose vigor, and all activity was over by the 29th. When the ash clouds had gone, the mountain was seen to have lost a considerable amount (some sources say, 72 m) of altitude, now again being lower than the Somma crest. A new crater about 700 m in diameter and more than 170 m deep had formed during the eruption; a small lake was observed at its bottom soon afterwards.
1744-1760 eruptive sub-cycle
Vesuvio showed no signs of renewed eruptive activity during the 7 years following the 1737 eruption but there were several periods of increased seismicity. A new intracrateral cinder cone began to form as Strombolian activity resumed sometime during 1744. In 1745, this cone had grown considerably and was looming high above the rim of the 1737 crater. Continuous Strombolian activity occurred through mid-1751.
1751 eruption. After a few days of increased seismicity and underground noises, Vesuvio became vigorously active at about 2200 on 25 Oct 1751 when a fissure tore open the SE flank and emitted a lava flow. This flow descended through the Atrio del Cavallo towards Boscotrecase but then turned towards Mauro (Bosco di Ottaviano). Lava movement ceased on 2 Nov, the flow stagnating without having reached populated areas, but after burning some forest (Roth 1857, reports that lava effusion continued until 25 Feb 1752). The summit cinder cone had already collapsed during the first days of lava effusion.
Small lava flows from the SE flank fissure continued until Feb 1752, and more vigorous summit activity occasionally caused ash falls.
Only steam and ash emission was observed during the remainder of 1752; Strombolian activity may have resumed at the crater floor during this period but first became obvious in late March 1753. From then on, the activity continued with frequent explosions and ejections of bombs and lapilli, forming a new cinder cone within the crater. A small lava flow spilled over the crater floor in July 1754.
1754 eruption. Another episode of much increased activity began on 2 Dec 1754 when a new effusive fissure opened on the E flank, sending two lava flows in the directions of Ottaviano and Mauro (Boscotrecase). Summit activity continued to build the cinder cone which by then had grown somewhat higher than the main crater rim. Lava emission from the flank fissure ceased in late Dec but apparently resumed at a minor scale in Jan 1755.
After the end of the flank eruption, summit activity continued unabated and significantly enlarged the summit cinder cone so that it was visible from Napoli early in 1755.
During the next 5 years, the summit cinder cone remained vigorously active, constantly changing its shape and size. This activity was repeatedly accompanied by minor lava flows within the crater, and on one occasion, by a brief lava overflow onto the W flank. On 20 March 1759, a large portion of the summit cinder cone collapsed, followed by the emission of lava that overflowed onto the outer flanks on 30 March. This episode was apparently of very brief duration. All activity was much reduced for most of the remainder of 1760, only to increase again in Nov of that year.
1760-61 eruption. The closing eruption of the 1744-60 cycle was a most peculiar example of a so-called "excentric" eruption because it involved the activity of a fissure on the lower, outer slopes of the old Vesuvian (Somma) edifice.
Activity increased notably on 12 Dec 1760 when detonations were heard in Napoli; several earthquakes were felt between 20 and 23 Dec while Strombolian activity occurred at the summit crater.
On 23 Dec, a fissure suddenly opened near the S base of the volcano, between the Camaldoli prehistoric cinder cone and another old flank vent, Fosso della Monaca, at only 250-290 m elevation. Twelve boccas initally displayed vigorous explosive activity, but soon large volumes of lava poured out of the lower boccas and began to advance towards Torre Annunziata. The flow fortunately did not invade populated areas and stopped only about 270 m from the coast.
On 29 Dec, the summit cinder cone collapsed; the emission of scoria and lava from the excentric craters continued until 28 Dec. Summit ash emission ceased on 7 Jan 1761. The 1760 flank boccas are still visible.
The 1760 eruption was different from most other sub-cycle closing Vesuvian eruptions of the 1631-1944 period in that it had the lowest historic flank craters and in that summit explosive activity was comparatively moderate.
After this eruption, the volcano remained inactive for at least 3 years.
1764-1767 eruptive sub-cycle
One of the shortest sub-cycles during the 1631-1944 period, this one began with a very gradual resumption of intracrateral activity. In 1764, "smoke" issued from a pit on the crater floor, "but one did not see the traces of real fire" (Mecatti, in Alfano & Friedlaender, 1929, p. 39). The emission of steam (and possibly ash) gradually increased through 1765; black ash plumes rose from the crater in Sep of that year, and Strombolian explosions from a small intracrateral cone were observed in early Nov. The activity became more and more vigorous during the first months of 1766, and on 28 March, lava overflowed the crater rim and moved sluggishly onto the W flank. Little activity occurred on the next day, but renewed lava effusion occurred on 30-31 March, and repeatedly until 9 April. A somewhat larger lava flow issued from a fracture system on the S and SE flank on 10 or 11 April, reaching the base of the main cone within a few days. After late April, lava emission decreased and continued at rather minor scale until mid-Dec. During this time, the summit cinder cone grew significantly but collapsed partially on 1 Sep.
After the end of the flank effusive activity, explosive activity from the summit cinder cone continued with varying intensity through Oct 1767, sometimes accompanied by brief periods of summit effusive activity. The changes in the shape and size of the cinder cone during this period (1766-67) have been beautifully illustrated by Hamilton.
From March until Sep 1767, the Strombolian activity from the summit cinder cone gradually increased, heralding another violent closing eruption.
1767 eruption. By the summer of 1767, the terminal cinder cone was again visible from Napoli, and lava frequently spilled over its rim indicating that the magmatic column stood at a very high level. On the morning of 19 Oct, lava began to pour rapidly from a new subterminal bocca some 90 m below the summit. Another vent became active at noon on the N flank at a somewhat lower elevation than the earlier bocca. Meanwhile, summit explosive activity increased dramatically, forming a tall eruption column and producing explosions that were well audible in Napoli. Still another effusive bocca became active at 1400 on the S flank, followed soon by another on the NW flank. Large lava flows began to move towards the Colle del Salvatore (the hill on which the Osservatorio Vesuviano was to be built in the mid-19th century) and towards Torre Annunziata. While the latter flow did not advance very far, the flow on the W flank travelled some 5.5 km from the summit. It threatened San Georgio a Cremano and surrounded the chapel of S. Vito but did not advance further into populated areas.
Very intense explosive activity occurred from the summit crater during 20-23 Oct, the detonations shaking buildings in Napoli; ash fell over the city and onto ships out in the sea to the W. On 24 Oct, the activity began to decrease, but ash continued to fall onto Napoli until the 26th. The last ash to be emitted on the late 26th had the usual white color telling the local residents that the worst was over for the time being.
Vesuvio then took a rest of more than 2 years.
1770-1779 eruptive sub-cycle
Strombolian activity resumed on 16 Feb 1770, after 27 months of repose. After an increase of the activity, an effusive fracture opened on the E flank on 16 March, and repeated episodes of slow lava extrusion took place from this site until April.
More significant activity began on 1 May 1771 when an effusive bocca formed some 200 m below the summit on the N flank. A lava flow rapidly reached the Atrio del Cavallo and then turned W towards Resina. A spectacular lava cascade about 30 m high developed in the Fosso di Collolla. Four spatter cones developed on the N flank fissure whose activity with repeated lava outpourings continued until late May. Fortunately, the lava did not invade populated areas.
After the end of the effusive activity, ash emission continued from the summit cinder cone. Strombolian activity further enlarged the cone that became more than 100 m high from its base in 1772.
No significant events took place until 29 Dec 1773 when lava overflowed the NNE rim of the summit crater. This effusive episode ended on 16 Jan 1774, but by this time, an effusive bocca had formed on the upper NNE flank that sent more lava down to the Atrio del Cavallo. Lava emission ceased in Feb but resumed on 4 Aug to continue through Dec. Strombolian activity continued afterwards, and the intracrateral cinder cone had further grown by mid-1775.
Lava overflowed the SE crater rim on 20 Dec 1775 and reached the caldera floor, ceasing on 2 Jan 1776. On the next day, lava began to issue from a fissure on the upper N flank and rapidly descended towards the caldera floor. More lava flowed downslope on the 5th as new fractures formed on the NW slope, and beautiful pahoehoe surfaces were present on the lava field that formed in the Atrio until 16 March. During the next 6 months, repeated effusive episodes occurred from numerous fractures that opened in the NW, N and S sectors of the cone. None of these flows came close within inhabited areas.
Activity continued essentially the same way during late 1776 and all of 1777 and 1778, with periods of lava effusion from fissures on the upper flank punctuating the usual summit Strombolian activity. This activity again became more notable in May when lava poured from a NNE flank fracture. After a temporary cessation in late June, lava emission resumed on 29 July, and on 2 Aug, another lava flow began to spill down the SE flank from a vent on the crater rim. During those days, the activity showed an overall increase that heralded one of the most spectacular closing eruptions since 1631.
1779 eruption. During the first week of Aug 1779, it became evident that Vesuvio was preparing for a grand celebration of the 1700th anniversary of its AD 79 eruption. The Strombolian activity of the summit crater gradually developed to a continuous lava fountaining on 5 Aug, while lava poured copiously down the upper flanks (this may also have been the cascading of incandescent spatter and scoria). Later that day, the crater platform carrying the summit cinder cone collapsed, and a large lava flow spilled over the crater rim, reaching the floor of the Atrio on the next morning. Widespread ash falls occurred around the mountain, with Pele's hair falling in Somma Vesuviana and Ottaviano. On the evening of 6 Aug, ash fell over the SE sector of the volcano. This was followed, still on 6 Aug, by a powerful lava fountain that must have risen hundreds of m above the summit. This short-lived paroxysm was but a shape of things to come.
The next day (7 Aug), vigorous ash emission and loud rumblings caused terror among the population; ash was driven to the N on this day. Intense lava fountaining resumed that evening, forming a huge fire fountain that lasted 4 hours. Most of the ejected coarse material fell onto the slopes of the active cone. On the next morning, the SE rim of the crater appeared significantly lowered, and a deep breach had formed towards this side.
During the 8th, relatively mild ash emission heralded the climax of the eruption that came with the renewal of the gigantic fire fountain at about 2000. This time, the phenomenon was more spectacular and more destructive than on the previous two evenings.
Accompanied by a loud roaring noise, the gigantic incandescent column rose to an altitude of 3 km or even higher. To the population of Napoli this was a frightening spectacle, but it was terror to those living on the N and NE flanks. A heavy rain of coarse pyroclastics fell onto the unfortunate town of Ottaviano and, though somewhat less, its neighboring town of Somma Vesuviana.
The luminosity of this huge lava fountain is said to have been as brilliant as to cause daylight brightness even as far as Napoli. A tall eruption column towered above the fountain, and ash fell hundreds of kilometers away.
More was yet to come. On the morning of 9 Aug, another lava fountain rose still higher than its predecessor, and more fall of large rock fragments occurred in Ottaviano. Severe damage and several fatalities were caused in this town and neighboring villages (Scandone et al. 1993b), but the number of people killed was relatively low due to the fact that the people had fled from their homes before the culmination of the eruption. The layer of pyroclastics must have been more than 1 m high. As Hamilton remarked, "had the eruption lasted one hour longer, Ottaviano would have suffered the fate of Pompeii and would have been buried."
Ash was again distributed over a large area and drifted as far as Albania.
The eruption rapidly lost vigor after this final paroxysm, and only a few episodes of explosive ash ejections occurred during the following days, completely ceasing on 15 Aug. Only a minor ash fall (maybe caused by an intracrateral avalanche) occurred on 4 Oct.
As a result of the violent gaseous outrush during the fire-fountains, a gaping crater had formed on the summit, and a layer of pyroclastics several tens of m thick had buried the former surface of the Atrio.
The mountain showed no signs of activity for the next 4 years.
1783-1794 eruptive sub-cycle
The first activity since 3 years occurred on 18 Aug 1783 when weak explosions opened a vent on the crater floor. This marked the beginning of Strombolian activity and the growth of a new intra-crateral cinder cone; both were accompanied by occasional lava outflows into the moat between the growing cone and the crater rim. The activity increased in Nov 1785 when lava began to pour down the NW flank. Lava emission continued at low rates and with brief interruptions for the next 4 years. The flows did not threaten populated areas, but destroyed a chapel in the Fosso della Vetrana. During this period, Strombolian activity was more or less continuous, with intensity fluctuations.
During a period of increased activity on 6-15 Sep 1790, the summit cinder cone grew notably, having several active boccas. Repeated lava flows occurred during this activity and sometimes large, dark ash plumes were formed.
After 15 Sep, repeated outflows of lava and occasional intense Strombolian activity continued until 20 Oct when lava emission ceased, but increased explosive activity continued until 17 Nov.
During 1791-92, Vesuvio displayed its normal persistent Strombolian activity, but no lava outflows took place. Only in May-June 1793, lava apparently flowed within the crater but did not reach beyond the crater.
The activity decreased to a very low level in late 1793 and early 1794; this time there was no significant build-up of the activity towards the final paroxysm such as usually was the case. The only precursors of the forthcoming eruption were unusual underground noises, the lack of water in wells near the volcano, and increasing seismicity that were observed in the first half of June 1794.
1794 eruption. For the third time since 1631 was Torre del Greco to become victim of Vesuvio's fury when the volcano opened the stage for another spectacular closing eruption that again involved the activity from an excentric fissure. The explosive activity was even more violent than in the 1779 eruption.
The eruption began quite abruptly with the splitting open of the volcano on its lower SW and NE flanks while powerful explosions blasted away the summit cinder cone and the crater platform. The NE flank fissure emitted a lava flow that covered the floor of the Atrio and did not extend into populated areas. However, large volumes of lava poured from the SW flank fissure on which 6 vents had formed between 325 and 550 m elev. The uppermost of these vents were displaying strong explosive activity. Meanwhile a tall eruption column rose from the volcano, and lava from the SW flank fissure rapidly advanced in the direction of Torre del Greco, reaching the walls of the doomed town within 6 hours, at about 0400 on 16 June. Little later, the lava had entered the town and began to consume street by street, until finally reaching the sea, leaving little of the formerly prosperous community behind. Vigorous magma-water interactions took place when the lava entered the sea, forming a new promontory extending some 190 m into the sea at a width of about 350 m. The volume of the lava flow (or possibly of all lava emitted both from the SW and NE flank fissures?) was about 2.7 x 10^7 m^3.
When the Torre del Greco lava flow stopped, explosive activity at the summit increased, and the mountain was concealed by ash clouds during the days of 16-18 June. There was little emission of incancescent material, but enormous amounts of ash were ejected, falling densely around the volcano, the clouds being traversed by incessant lightning bolts. On the evening of 17 June, the summit was blasted away or collapsed, the products of this event blocking the conduit that had to blast itself free again. A heavy shower of large lithic fragments fell over Ottaviano, the town that has so often been the most seriously affected community by tephra falls from Vesuvio. It is likely that it was this rain of coarse pyroclastics which caused the 26 fatalities attributed to this eruption (in their list of Vesuvio's eruptions, Scandone et al., 1993b, put the number of casualties of the 1794 eruption at more than 400).
The heavy fall of ash continued unabated on 18-26 June, then gradually decreased although still falling abundantly, through 7 July. Heavy rainfalls mobilized the fallen ash to form mudflows during late June and early July, adding to the destruction brought by the erupton itself.
When the eruption finally ceased, the mountain presented a drastically changed profile: the steep summit had gone, leaving a vast crater behind. The highest point of the crater rim was in the NE at 1203 m elevation, which was reportedly 121 m lower than before the eruption (this values appears somewhat high since the greatest elevation ever reached by the volcano was 1335 m in May 1905 [see below] and it appears unlikely that it had already been so close to this height more than 100 years earlier - 100 years that were to significantly contribute to the growth of the cone). The new summit remained a long-lastig topographic reference feature named Punta del Palo.
An estimate of the volume of pyroclastics emitted during the 1794 eruption gives about 5.05 x 10^8 m^3; also this value appears exaggerated (the much more violent 1906 eruption is known to have ejected about 2.5 x 10^8 m^3 of juvenile tephra only). Nonetheless, this eruption was certainly the most violent and devastating since 1631. A similar eruption today would cause a disaster of unbelievable proportions (but the eruption to be expected after several decades of inactivity will be more violent).
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This page was last modified on 12 June 1996