Report on Etna (Italy) — 11 December-17 December 2013
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 11 December-17 December 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, 11 December-17 December 2013. Smithsonian Institution and US Geological Survey.
37.748°N, 14.999°E; summit elev. 3295 m
All times are local (unless otherwise noted)
INGV reported on the 20th paroxysm in 2013 from Etna’s New Southeast Crater (NSEC) began with a strong explosion at 0925 on 14 December from a vent near the NE rim which generated an ash plume that rose 2 km. Intermittent ash emission gradually turned into Strombolian activity. After 1413 the activity intensified; small ash puffs were produced and Strombolian explosions ejected incandescent pyroclastics onto the flanks of the cone. Over the next few hours activity continued to intensify and a diffuse ash plume drifted ESE. At 2323 lava overflowed the SE crater rim and flowed towards the Valle del Bove. During the night explosive activity continued to intensify, and by 0330 on 15 December Strombolian activity was intense and virtually continuous. After 0500 explosive activity started to diminish, and at 0550 the volcanic tremor amplitude and the intensity and frequency of Strombolian explosions showed a sharp drop. Explosive activity continued to produce copious amounts of ash until about 0830. According to a news article, the ash emissions caused the cancellation of more than 20 flights in and out of the Catania airport.
At 0610 and 0633 two vents opened within the deep trench cutting the SE flank of the NSEC cone (where lava was still flowing from the crater since the previous evening), the first just a few tens of meters below the crater rim, the second about 100 m further downslope. Both vents initially produced lava fountains for a few minutes, with jets a few tens of meters high, and then produced lava flows that descended through the trench.
Between 0945 on 15 December and the morning of 16 December ash emission varied in frequency and intensity, related to variations in the intensity of the Strombolian activity at NSEC. During the afternoon and evening of 15 December explosive activity lasted a few to a few tens of minutes and Strombolian activity became significantly more intense or passed into pulsating, low lava fountains. The more intense periods produced greater amounts of ash leading to ashfall in populated areas on the E and SE flank, from the Milo-Zafferana area toward the Ionian coast. At night during 15-16 December lava flows continued to flow towards the Valle del Bove. A shift in wind direction caused ashfall in areas SE, S, and SW.
On 15 December small and periodic ash emissions also occurred from Northeast Crater. Small thermal anomalies detected with a thermal camera were detected during 15-16 December.
Strombolian activity at the NSEC continued through 16 December at a slowly decreasing rate and with numerous minor intensifications that generated diluted ash plumes. Lava effusion also gradually diminished, but at about 1430 on 16 December, a short fissure opened on the lower NE flank of the NSEC cone, producing a small lava flow which advanced a few hundred meters. Explosive activity finally ceased around midnight on 17 December. Very slow lava effusion continued, at a gradually decreasing rate, from the fissure on the NE flank of the NSEC cone, through the night of 17-18 December.
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.