ACTIVITY OF VESUVIUS BETWEEN
1631 AND 1944
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The eruption of Vesuvius of March 1944, is the last eruption
occurred at Vesuvius. Since then the volcano has been in a quiescent stage
without any major sign of activity.
Between the great eruption of 1631 and 1944 Vesuvius , is almost always in activity with only brief periods of quiescence not exceeding 7 years. Major eruptions occurred in 1794, 1822, 1834, 1850 e 1872. After1872 slow lava effusions, lasting several years formed small lava accumulation (lava domes) in the proximity of the crater. One of this, named Colle Umberto, formed between1895 and 1899 in the area between the cone and the Observatory.
In 1872, after the eruption, Vesuvius cone had its maximum elevation at 1335 m a. s.l.. In May, 1905, a new eruption began, firstly with slow lava effusions and, since January, 1906, with intermittent explosive activity (strombolian activity). On the 7th of April, 1906 the eruption reached the climax with lava fountains and earthquakes. The eruptive column of ash and gas reached the height of 13000 m. The eruption ends in the last days of April.
During the eruption of 1906 the top of Vesuvius was truncated
and formed a vast crater with a diameter of approximately 500 m and a depth
of 250 m. The crater rim was lowered to 1145 m asl at its minimum height.
After the eruption
there was short period of quiescence followed by a prolonged period of permanent activity since 5 July of 1913. This activity , caractherized by quiet effusion of lava and minor explosion from a small conelet, slowly filled the 80 million m3 crater left by the eruption of 1906. By 28 November of 1926 the crater had been filled up to its lower edge (~1070 m) and from that time on, small lava flows descended along the slopes of the crater. In June 1929 a major lava flow extended outside the Somma caldera rim and reached the village of Terzigno on the eastern slope of the volcano. The lava flow emission was followed by a phase of lava fountaining accompanied by sustained seismic tremor. By 1944 the lava field had almost filled up all the extension of the crater up to the altitude of about 1140-1150 m asl. Only a few remains of the original crater were visible especially on the south-western rim , where was located the highest point of the crater at 1186 m asl. The conelet, built at the center the lava field, had reached an height of ~1260 m asl.
On 6 January, 1944 there was an lava flow from the conelet that rapidly reaches the border of the rim and outflows. The small lava flows continues until 26 January outside the rim and until 23 February within it. On that day the activity ends.
THE ERUPTION OF 1944
On March 13, 1944 the conelet partially collapsed forming
a depression of about 20 m depth. A slight explosive activity partially
rebuilt the conelet on the 14th. This activity lasted intermittently till
the 18th. At 16.30 (local time) of the 18th a lava flow was rapidly emitted
form the remains of the conelet, overcome the crater wall on the northern
side and reached the Somma caldera wall below the Punta del Nasone.
On the evening of 18 March there are several lava flows on Gran Cono. On the evening of 19, at 11am , the northern flows reaches Fosso della Vetrana and , in the evening, the first houses of Massa and S. Sebastiano. The villages are invaded by the lava flows that reaches a distance to 1,5 km from the central Cercola (22 March).
The fist lava fountain starts on March 21 at 21:17 and last for about 30 minutes causing an accumulation of scaoriae on the flank of Gran Cono. Other 7 lava fountains last until the next day
The last lava fountain culminates with the formation of a sustained ash plume which reaches about 5 km above the crater rim. This phase and the following one are accompanied by the formation of small pyroclastic flows on the flank of the volcano.
On 27 e 28 the explosions are more rare and less violent, on 29, the eruption ends.
On 29 March, the crater, lay like on an plane piano inclined from north-east to south-west, has a maximum depth of 300 m with respect to the rim and a perimeter, of 1,6 Km. The western rim has an height of 1.169 m as.l. and the north-east 1.300 m asl.
The effects of the eruption
The eruption of Vesuvius of 1944 occurs shortly after the arrival in Naples of the allied forces in world war II. Because of war the Vesuvius Observatory is a metereological station of armed forces and the Observatory director, Giuseppe Imbò, occupies only one room to make its fundamental observations of the eruption. the eruption caught by surprise the militaty and destroyed the airforce planes stationed in the airport of Terzigno east of the mountain. An entire wing of 88 B-25 was damaged by the eruption. There were a few casualties caused by the explosion of a water tank invested by a lava flow. The major economic losses resulted by the destruction of the villages of S.Sebastiano and Massa by the lava flow.
The crater rim has
an elliptic form with a major axis of 580 m (east-west) and a minor of
480 m (north-south). The shape a the crater is modifid by subsequent collapses
tha continue til the present time.
In the following table is reported the detailed chronology of the main phases of the eruption.
|March 18, 1944|
|16.30||Eruption begins with a lava flow|
|22.30||velocity of lava flow within the Valle del Gigante ~10 m/h|
|23.00||outpouring of a lava flow to the W, the funicolar is interrupted between the stations of Eremo and Funicolare Inferiore. New lava flow toward SW|
|11.00||The northern flow reaches the limit of the Fosso della Vetrana. Increase of explosive activity with lapilli and scoria thrown up to 150 m|
|afternoon||volumetric flux of the northern flow: ~200.000 m3/h|
|Night||increase of effusive activity;a new flow overlaps onto the northern flow, at 6.30 the new flow reaches the Fosso della Vetrana|
|01-02 am||San Sebastiano and Massa are reached by the lava flow. Velocity of the front ~50-100 m/h|
|21 17 h||Beginning of the II phase (lava fountains) scoria
and lapilli thrown up to height of 500-2000 m. Strong decrease
in the outpouring of lava. The fall back of scoria produced
incandescent scoria flows.
I fountain 17.15-17.35
II fountain 20.10-20.30
III fountain 22.00-22.25
|07.31, lasts till 17.50||VIII fountain, with the formation of a sustained eruption
plume. Scoria of 500-1000 g fall onto Poggiomarino.
From 10.00 scoria fall onto S.Giuseppe (maximum diameter between 5 -15 cm. From 12.48 the lava fountain transforms into an ash plume that reaches an height of ~5-6 Km above the crater rim . The activity is accompanied by the formation of small pyroclastic flow on the sides of the cone. The activity comes to an ed at 17.50
|20.00||Wet ash fall onto S.Giuseppe|
|21.00||Several explosions with the emission of two distict plumes on the souther and northern margin of the crater.|
|Ash fall accompanied by lithics onto Torre del Greco; at S.Giuseppe there is a fall of lapilli embedded into an ice layer. Seismic crysis between 11 and 12h. Fall of red lapilli, crystals and small pumice onto Poggiomarino. This kind of activity continue with a decreasing intensity until the 29. At this time the crater with a volume of 25x106 m3 and a depth of 300 m is already formed|
The sequence of events that occurred during the eruption of 1944 is similar to those of other eruptions occurred at Vesuvius in the period between 1631 and 1944, like for example the eruption of 1906 described by Perret. Notably these eruptions begin with an emission of lava flow followed by strong lava fountains and finally by an explosive phase with a sustained eruption column. The estimates of the magma discharge rate of the different phases of 1944 eruption suggest that the the shift to the more explosive character of the eruption is probably related with an increase of the volumetric discharge.
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