Report on Etna (Italy) — December 2000
Bulletin of the Global Volcanism Network, vol. 25, no. 12 (December 2000)
Managing Editor: Richard Wunderman.
Etna (Italy) Summary of July to November 2000 notes small lava flows, Strombolian eruptions
Please cite this report as:
Global Volcanism Program, 2000. Report on Etna (Italy) (Wunderman, R., ed.). Bulletin of the Global Volcanism Network, 25:12. Smithsonian Institution.
37.748°N, 14.999°E; summit elev. 3295 m
All times are local (unless otherwise noted)
This summary of Sistema Poseidon reports covers the period from July to November 2000. The summit craters discharged several minor lava flows, some Strombolian eruptions, and frequent degassing. The Bocca Nuova (BN) vent was particularly active.
During July and well into August the summit craters displayed comparatively low activity. During July at BN three different vents were degassing. During July at NEC emissions came from one primary vent. Emissions were robust on 18 August, and commonly bore light-brown ash.
During late August, Southeast Crater (SEC) renewed emission of a weak lava flow from a fracture on the N side. The lava stream, which flowed into the Valle de Bove, persisted throughout 27 August, and increased progressively on the night of 27-28 August.
At 0135 on 28 August fairly sustained degassing occurred at SEC with initially violent Strombolian emissions. Beginning at about 0600, the explosive Strombolian activity changed rapidly to violent lava fountains, which generated an eruptive cloud rising thousands of meters above the summit. Ash and lapilli fell on the Etna's E slopes. This phase lasted about one hour, and was analogous to what had been observed during episodes in the first half of 2000.
The lava flow, despite appearing larger during the more violent degassing phase, moved little on its farthest-advanced fronts, which along the W face of the Valle del Bove reached to about 2,200-2,300 m elevation. Rather, the flow tended to widen in the zone between 2,800 and 2,700 m. The lava emission rate at the vent appeared to be drastically reduced at the end of this degassing phase.
A new degassing episode was confirmed on 29 August. This was characterized by its brevity and by the way in which it manifested itself, producing explosive Strombolian blasts (rhythmic expulsion of pyroclastics) rather than true lava fountains.
As frequently observed for the last episode, this one also started with a glimmer of light on the N flank of the SEC announcing the beginning of a new lava emission. Eruptive activity increased between 22 and 28 August, while the volcanic tremor first showed a modest increase at 0339 on 29 August, when sporadic explosions from the SEC summit crater began. Only after 0530 did the explosive activity reach a continuous intensity. It concluded at about 0610. Peak activity did not reach the same levels as the preceding phase, but ejected pyroclastics ~200 m above the crater rim. The finer portions were carried several hundred meters and dispersed E, without reaching residential areas.
Observations at the conclusion of the late-August explosive phase showed the new lava flow still spreading over the N flank of the SEC, but new lava had ceased venting. This new flow overrode the one from 28 August, and descended to ~2,100 m on the W face of the Valle del Bove.
The other craters in the volcano's summit area chiefly slowly emitted gas vapors, with the exception of one of BN's vents, which frequently ejected brown ash. The emission of ash from this vent intensified during the week. As September began, BN continued to produce abundant steam and ash emissions, which at times seemed aided by elevated atmospheric humidity and by infiltration of recent precipitation. This effect continued later into September.
In mid-September, BN produced generally mild degassing. During 19, 22, and 23 September nearly continuous ash emission took place. Primarily dark gray and sometimes brownish colored plumes were visible for many kilometers. For the preceding weeks these plumes had vented at two distinct crater cavities on the inside of the BN. The larger cavity lies in BN's center and discharged gaseous blue-white emissions. The smaller cavity lay near BN's internal SW wall, and it expelled ash. During this same time, as in past weeks during the month, the Voragine and Northeast Crater continued to emit abundant steam. The SEC weakly degassed from fumaroles.
October activity continued as in past months with ash emissions at the BN. These were particularly visible on 3-6 October. At night it was possible to observe light coming from the crater cavity on the inside of the BN, suggesting weak Strombolian activity. Mid-October behavior included explosive Strombolian eruptions from both crater cavities; incandescent bombs occasionally fell outside of the crater. Milder episodes occurred on 17 and 21 October. Between 24 and 29 October two stronger episodes took place.
At the Voragine and the NEC, the early days of October showed rather sustained steam emissions, in part accentuated by the first snowfalls and by the elevated humidity on the summit. The SEC displayed mostly fumarolic activity. Later, the Voragine gave off copious steam, but at the SEC and NEC weak degassing occurred.
The last days of October and the early days of November were distinguished by a decline of the explosive Strombolian activity from the two emission points within BN. Strombolian activity sent tephra ~100-150 m high, which still frequently fell outside of the BN crater.
During November, BN continued to produce modest explosive Strombolian activity that sometime spewed incandescent material of moderate size outside the crater walls. Observers continued to note two distinct cavities in BN.
In the early hours of 29 November observers noted the presence of a small lava flow at the base of the SEC. Upon close viewing, observers found that the flow gushed from the base of a fracture on the N sector of the cone at the SEC and continued downslope for ~200 m. Although lava continued to flow in the succeeding days, atmospheric conditions obscured later views of this area. No relevant activity aside from a constant steam emission occurred either at the Voragine or at the NEC during this time.
Geologic Background. Mount Etna, towering above Catania, Sicily's second largest city, has one of the world's longest documented records of historical volcanism, dating back to 1500 BCE. Historical lava flows of basaltic composition cover much of the surface of this massive volcano, whose edifice is the highest and most voluminous in Italy. The Mongibello stratovolcano, truncated by several small calderas, was constructed during the late Pleistocene and Holocene over an older shield volcano. The most prominent morphological feature of Etna is the Valle del Bove, a 5 x 10 km horseshoe-shaped caldera open to the east. Two styles of eruptive activity typically occur, sometimes simultaneously. Persistent explosive eruptions, sometimes with minor lava emissions, take place from one or more summit craters. Flank vents, typically with higher effusion rates, are less frequently active and originate from fissures that open progressively downward from near the summit (usually accompanied by Strombolian eruptions at the upper end). Cinder cones are commonly constructed over the vents of lower-flank lava flows. Lava flows extend to the foot of the volcano on all sides and have reached the sea over a broad area on the SE flank.
Information Contacts: Sistema Poseidon, a cooperative project supported by both the Italian and the Sicilian regional governments, and operated by several scientific institutions (URL: http://www.ct.ingv.it/en/chi-siamo/la-sezione.html).