Report on Etna (Italy) — 30 January-5 February 2013
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 30 January-5 February 2013
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2013. Report on Etna (Italy). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 30 January-5 February 2013. Smithsonian Institution and US Geological Survey.
37.748°N, 14.999°E; summit elev. 3295 m
All times are local (unless otherwise noted)
Sezione di Catania - Osservatorio Etneo reported that intense Strombolian activity at Etna's Bocca Nuova Crater began on the evening of 30 January and was the fifth episode of activity during a three-week interval that began on 10 January. Weak glow from a vent on the SE part of the crater floor was first observed at 1807. The glow became stronger and was visible to nearby residents; simultaneously volcanic tremor amplitude rapidly increased, and shifted from below the New Southeast Crater (NSEC) toward Bocca Nuova. Between 1900 and 1915 the activity intensified, and from 1920 onward jets of incandescent volcanic bombs and scoria nearly continuously rose higher than the crater rim. Some tephra was ejected 150 m above the rim.
During 1930-2000, lava fountains rose 100 m above the rim. Shortly after 2000, the fountain leaned SW and produced heavy fallout of incandescent bombs and scoria on the outer SW flank of the central summit cone, down to its base. At 2016 the fountain rose vertically and pyroclastic fallout outside the crater diminished.
Around 2030 the lava fountain started to wane; the incandescent jets became discontinuous and only rarely rose more than 100 m above the crater rim, except for one jet, at 2100, which rose 150 m above the rim. In addition, the volcanic tremor amplitude rapidly decreased and returned to normal levels in the late evening. After 2200, the incandescent pyroclastic jets no longer rose above the crater rim, and the glow became progressively less brilliant. During the night, however, weak eruptive activity continued on the crater floor, evident from a dull glow emanating from the crater. During the early morning hours of 31 January, the glow gradually faded away, and the episode ended with a series of sporadic, small ash emissions, the last of which was seen around 0641.
During 31 January-1 February ash emissions at New Southeast Crater (NSEC) were nearly continuous for intervals lasting from a few minutes to more than one hour. On 1 February small discrete "puffs" of ash rose from Bocca Nuova. At both craters ash plumes rose no higher than 100 m above the crater rims.
At 0300 on 2 February a camera recorded weak glow from NSEC then after 0330 sporadic small explosions ejected incandescent pyroclastic material up to a few tens of meters above the crater rim. The strongest explosions (at 0345, 0400, 0409, and 0411) ejected glowing bombs onto the flanks of the NSEC cone. Two minutes after the last of the explosions, weak glow appeared at Bocca Nuova that only lasted a short time; during the following 30 minutes, however, intermittent glow was recorded at both craters. At 0450 jets of lava rose above the rim of Bocca Nuova; at 0500 Strombolian activity became continuous, producing jest that rose many tens of meters above the rim. Small Strombolian explosions resumed in NSCE at 0512. Just after 0515 activity at Bocca Nuova started to increase rapidly; contemporaneously, the volcanic tremor amplitude showed a sharp rise. Lava fountains rose 120-150 m above the rim. Activity at NSEC started to decrease at 0530 then ceased just before 0600. Activity at Bocca Nuova decreased markedly between 0620 and 0630; weak intracrater activity continued for a few more hours and then by 0900 the episode was over.
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.