Report on Etna (Italy) — 13 July-19 July 2011
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 13 July-19 July 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, 13 July-19 July 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 the evening of 11 July Strombolian activity began from Etna's Bocca Nuova crater, representing the first magmatic eruption since 2002. Incandescence was first recorded with a monitoring camera on the SE flank and was later visible from population centers in the SE sector of Etna. During the night of 12-13 July incandescence was more continuous and intense than during the previous night. At varying intervals, incandescent bombs that were ejected above the crater rim fell back into the crater. On 13 July volcanologists visited Bocca Nuova and observed a single large vent on the crater floor that was the source of the Strombolian activity. The strongest explosions ejected incandescent bombs several tens of meters above the crater rim. Most bombs fell back into the crater but some went over the rocky partition that divided Bocca Nuova from Voragine, and fell into the S portion of the latter.
In the evening of 15 July, volcanologists again visited Bocca Nuova and noted that the Strombolian activity had decreased slightly but within less than two hours had increased to levels greater than those observed on 13 July. Immediately to the W of the explosive vent, a lava flow was issuing from underneath a sheet of pyroclastic material deposited by the nearby Strombolian activity. The flow cascaded into a deeper depression in the W central portion of the crater floor.
On 16 July, a series of ash emissions from the pit crater located on the E flank of the SE Crater cone marked the resumption of explosive activity within the crater, and produced loud booming sounds that were widely heard in populated areas on Etna's flanks. On the evening on 18 July Strombolian activity increased and culminated into a new paroxysmal eruptive episode on 19 July. Lava flows traveled down the steep W slope of the Valle del Bove, following the same path as the lavas emitted during the preceding eruptive episodes, and stagnated at the base near Monte Centenari. Lava fountains rose 200-250 m and produced heavy fallout of fluid spatter, forming several lava flows. The largest lava flow descended the S flank of the cone reaching the base. A dense plume of gas and ash drifted 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.