Report on Etna (Italy) — 13 March-19 March 2013
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 13 March-19 March 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, 13 March-19 March 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 Strombolian activity continued at Etna's Voragine Crater after the 5-6 March paroxysm at the New Southeast Crater (NSEC), but was rarely detected by 14 March. Sometime during the afternoon of 15 March, numerous explosion signals were detected, and the volcanic tremor amplitude increased through the evening. After nightfall, incandescence from the NSEC was visible, and nearby residents (on the SE flank) heard loud bangs coming from the crater. This activity continued during the night and through the following morning. At daybreak on 16 March, numerous gas rings formed by the more powerful explosions were recorded by the monitoring cameras and photographed by observers in the field.
During the early afternoon of 16 March, activity started to intensify more rapidly, and frequent jets of incandescent lava were launched up to150 m above the crater rim. At about 1800 lava started to flow through the deep breach in the SE rim of NSEC. Approximately 15 minutes later, explosions became progressively more energetic, ejecting incandescent bombs onto the outer flanks of the cone; contemporaneously, the quantity of pyroclastic material (ash and lapilli) in the eruptive plume increased. Ash plumes drifted SE.
Between 1830 and 1845, the eruptive activity changed from Strombolian explosions to lava fountaining, with the highest jets rising 600-800 m above the crater rim. The eruption column rose about 2 km above the summit of Etna before it was blown SE by the strong winds. Around 1900, several lightning flashes within the eruptive cloud were observed. Large, incandescent bombs and scoriae were deposited on the entire cone of the NSEC and the adjacent areas to the S and SE. Observations made after the end of the paroxysm revealed that a lava flow was emitted from the area of the saddle between the SEC cones. During the phase of most intense lava fountaining, numerous volcanic bombs fell onto the pyroclastic cones formed during the 2002-2003 eruption, up to 2 km from the NSEC. In this phase, the lava fountains were also spectacularly visible from the town of Randazzo, on the NNE flank, about 15 km from the NSEC.
Heavy tephra fall, mostly in the form of scoriaceous lapilli, affected the SE flank; on the W headwall of the Valle del Bove this material was still incandescent. Further downslope, in the towns of Zafferana Etnea, Santa Venerina, and a number of villages to the N of Acireale, the tephra fallout formed a continuous deposit of scoriaceous lapilli, which in the N portion of Zafferana Etnea locally was up to 10 cm thick. Many clasts in this area had diameters from 5 to 8 cm, and more rarely up to 10 cm. Numerous car windshields, skylights, and roof tiles were broken. Even on the Ionian coast, the deposit consisted largely of lapilli, with only a minor fraction of ash.
The activity started to decrease around 1904, and at 1910 the activity evolved into violent explosions that ejected broad fans of large, incandescent bombs, accompanied by loud bangs and detonations. These explosions ceased at 1920, but at 1927 two particularly powerful explosions ejected large incandescent rock fragments towards the SW at least 1.5 km from the crater. A few weaker Strombolian explosions occurred shortly after 1930. At 0449 on 17 March, a series of explosions started at Voragine, which continued for about 5 minutes, generating strong thermal anomalies that were recorded by the thermal surveillance camera, and probably produced small ash puffs. During the next few hours, weak glow coming from Voragine was recorded by a monitoring camera. There were also small collapses and slides of still hot material from unstable portions on the NSEC cone, which generated minor quantities of ash.
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.