Report on Etna (Italy) — 9 November-15 November 2011
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 9 November-15 November 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, 9 November-15 November 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 eighteenth paroxysmal eruptive episode of 2011 took place at the New SE Crater (New SEC) of Etna during the morning of 15 November. Thermal monitoring cameras at the observatory in Catania and at Montagnola, about 3.5 km S of the summit craters, recorded a small thermal anomaly at the lower end of the eruptive fissure on the SE flank of the cone at about 0700. The anomaly slowly grew in size and temperature, caused by the emission and expansion of a small lava flow. Mild Strombolian activity commenced at 0900 from within the New SEC, and spattering began from several vents along the fissure on the SE flank of the cone. This activity continued for nearly three hours, while increasing very slowly, and the lava flow spread out into several branches at the SE base of the cone, advancing only a few hundred meters. At about 1155, the activity markedly and rapidly increased both within the crater and along the fissure, and just after 1200 lava fountains and ash emissions rose from the crater. Lava fountains then rose from vents along the SE flank fissure. Bombs and scoria fell into the cone.
At 1230 ash emissions significantly increased, especially from a vent located in the SE portion of the New SEC, and a plume of ash and gas rose several kilometers above the summit and drifted SE. The most intense phase of the eruption occurred between 1245 and 1315 when jets heavily laden with incandescent bombs rose as high as 800 m above the crater. Pyroclastic material fell onto the New SEC cone, areas well beyond the base, and the nearby old SEC cone. During this phase explosions occurred from a vent on the N flank of the New SEC cone, likely the same vent that emitted small lava flows on 28 September and 8 October. At about 1325 the activity started to diminish and ceased abruptly at 1329, but was followed by passive ash emissions that lasted until just after 1400. Weak and discontinuous spattering accompanied by slow lava effusion continued for a few hours from a single vent in the central portion of the eruptive fissure on the SE flank of the New SEC cone.
Lava flows from the eruption traveled less than 4 km toward the floor of the Valle del Bove, immediately to the N of the Serra Giannicola ridge, stagnating to the SW of Monte Centenari. The New SEC grew in height by 10 m on the S side, bringing the total height of the cone to about 180-200 m above its base. Ash and lapilli deposits affected the SE flank, including the towns of Zafferana Etnea (10 km SE) and Acireale (20 km SE).
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.