Report on Etna (Italy) — 5 January-11 January 2011
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 5 January-11 January 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, 5 January-11 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)
After a few hours of quiescence on the evening of 3 January, very weak emissions of incandescent material (probably mostly hot gas with little or no solid material) resumed from the pit crater located on the lower E flank of Etna's Southeast Crater cone. Later that evening intense incandescence from the pit crater was reported by observers in the village of S. Alfio on the E flank of Etna. The emissions continued on 4 January at a rate of 4-6 events per hour, producing small plumes that appeared as thermal anomalies in thermal video footage. Activity ceased in the afternoon. Very weak emissions of incandescent material (probably again mostly hot gas) were observed on 5 January at the same rate as the previous day. A camera recorded white vapor plumes occasionally accompanied by some grayish-brown ash. Weak, intermittent incandescence from the pit crater was observed at night during 5-6 January. Emissions on 6 January occurred at a frequency of 3-4 events per hour, producing small plumes seen in thermal camera footage. That same day, intense degassing occurred from the W vent of Bocca Nuova (BN-1), and from the Northeast Crater, where pulsating emissions produced mushroom-shaped vapor plumes.
Starting in the late evening of 11 January, the seismic network recorded a slight increase in volcanic tremor amplitude. The amplitude peaked early on 12 January, and the source of the tremor shifted from a location N of the Northeast Crater towards the Southeast Crater. Weak Strombolian activity from the pit crater accompanied these changes on 11 January, and gradually became more intense on 12 January.
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.