Report on Etna (Italy) — 10 August-16 August 2011
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 10 August-16 August 2011
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2011. Report on Etna (Italy). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 10 August-16 August 2011. 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 on 11 August sporadic ash emissions from Etna's New SE Crater produced small grayish-brown ash plumes. Thermal surveillance cameras revealed hot material in late-afternoon emissions. In the evening and throughout the night small Strombolian explosions were observed at intervals of a few tens of minutes. Early on 12 August, the day of the tenth paroxysmal eruptive episode of 2011, the Strombolian activity intensified and was accompanied by an increase in volcanic tremor amplitude. Strombolian explosions then produced dark ash clouds, and lava overflowed the E rim of the crater through a deep breach formed during previous eruptions. During the following 30 minutes or so Strombolian activity rapidly intensified, and formed a pulsating lava fountain about 100 m tall. Fifteen minutes later a dense column of ash rose above the lava fountain while large bombs and blocks fell onto the cone surrounding the New SE Crater.
During the most intense period three vents in the crater were active, two in the central portion and one close to the E-rim breach. Soon after, the two vents in the center of the crater emitted only ash, while the E vent continued to eject jets of incandescent lava. The activity completely ceased more than a half an hour later. The lava produced during the eruption descended the W slope of the Valle del Bove in numerous lobes; the most advanced lava fronts reached the base of the steep slope above Monte Centenari. Ash- and lapilli-fall affected a relatively narrow area between Zafferana (10 km SE), and the coastal area between Giarre and Acireale, on the SE flank.
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.