Report on Etna (Italy) — 5 October-11 October 2011
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 5 October-11 October 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 October-11 October 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 the sixteenth paroxysmal eruptive episode of 2011 took place at the New SE Crater (New SEC) of Etna during the afternoon of 8 October. A rapid increase in volcanic tremor amplitude was detected that morning, and at about 1300 weak and discontinuous Strombolian explosions were recorded by surveillance cameras. Two hours later, lava flowed from a deep notch in the SE rim of the crater.
At around 1545 vigorous Strombolian activity was observed from numerous vents along a short fissure on the SE flank of the cone, which had first been active during the 29 August paroxysm (the twelfth). Weather conditions deteriorated at about 1615, preventing direct observations of the Strombolian activity changing into sustained lava fountaining and ash emissions. However, this change was audible around 1630, and a dense ash-and-vapor plume rapidly rose above the weather clouds and drifted E. At the same time lava flows descended on the W slope of the Valle del Bove. Eruptive vents opened on the NE flank of the cone, approximately along the fracture that first opened during 8 September, and two small lava flows were emitted. The more voluminous lava flow traveled a few hundred meters downslope. The paroxysmal phase lasted a little longer than 20 minutes and ended around 1650. Ash emissions continued until 1945, when the volcanic tremor amplitude returned to levels similar to those preceding the paroxysmal episode, and the lava flow fronts appeared to stagnate. The ash cloud drifted ENE and produced ash- and lapilli-fall in a narrow sector from the Ripe della Naca area and the village of Puntalazzo (13 km E) to the town of Mascali (18 km E).
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.