Report on Etna (Italy) — 6 February-12 February 2013
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 6 February-12 February 2013
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2013. Report on Etna (Italy). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 6 February-12 February 2013. 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 during the days following the 2 February eruptive episode at Etna intermittent emissions of small quantities of ash were repeatedly observed from both the New Southeast Crater (NSEC) and Bocca Nuova Crater.
Volcanologists visited Etna on 5 February and observed the recent changes that had taken place at Bocca Nuova Crater, notably the growth of a pyroclastic cone surrounding the eruptive vent in the SE portion of the crater. This cone had grown at least 50-70 m, about halfway up the inner crater wall, and was leaning into the wall. The entire crater floor was covered with recent lava.
Later in the evening of 5 February a webcam recorded weak Strombolian activity at NSEC, which continued until daybreak the next day, and then became invisible due to deteriorating weather conditions. Seismic data showed an instantaneous increase of tremor at 1020; volcanic tremor amplitude rose to a peak within a few minutes after the start of the activity, and began to descend after less than one hour. People in the ski area on the NE flank of the volcano briefly saw a dense but ash-free gas plume rising from the summit.
After the episode on 6 February through most of 8 February sporadic ash emissions from NSEC were observed, although poor weather conditions often prevented observations. On the evening of 8 February weak glow from NSEC was intermittently visible. At 2100 a webcam recorded fluctuating glow from within Bocca Nuova which became more intense over the next 10 minutes. Around 2125 jets of incandescent lava were repeatedly seen rising above a thick blanket of clouds drifting over the summit area of Etna. Contemporaneously, the volcanic tremor amplitude rose sharply. After 2200 the volcanic tremor amplitude began to decrease, whereas the eruptive activity continued without showing signs of diminishing until about 30 minutes later. After 2230 on 8 February and during 9-10 cloud cover prevented observations. A brief ash emission was observed on 10 February.
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.