Report on Etna (Italy) — 29 December-4 January 2011
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 29 December-4 January 2011
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2010. Report on Etna (Italy). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 29 December-4 January 2011. Smithsonian Institution and US Geological Survey.
37.748°N, 14.999°E; summit elev. 3295 m
All times are local (unless otherwise noted)
INGV-CT reported that during the first few days of December gas emissions from a large pit crater on the lower E flank of Etna's Southeast Crater cone nearly ceased. On 22 December at 0446 a strong explosion occurred at the W vent of the Bocca Nuova (BN-1). This event generated an ash plume a few meters high, which then drifted NE, causing light ashfall in areas as far as the town of Linguaglossa (17 km NE). On 23 December bluish gas rose from a vent at the base of the W wall of the pit, at the base of the Southeast Crater cone. Bright incandescence was intermittently visible on video footage. Inclement weather prevented clear observations that day and during the next few days. On 29 December extremely small amounts of incandescent material emitted from the pit crater were observed using visible and thermal cameras. The brief emissions (2-6 second intervals) were jets of mainly hot gas that barely rose above the rim of the pit crater. Inclement weather again prevented observations of the crater during 30-31 December.
During the late afternoon on 2 January, strong incandescence at the pit crater evolved into vigorous Strombolian activity. Frequent Strombolian explosions (1-3 per minute) ejected coarse-grained incandescent material a few tens of meters above the rim of the pit. On a few occasions, incandescent bombs fell outside the pit's rim, mainly to the S and E. The activity continued into the early morning then decreased markedly. Negligible quantities of volcanic ash were produced.
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.