Report on Etna (Italy) — 2 December-8 December 2015
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 2 December-8 December 2015
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2015. Report on Etna (Italy). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 2 December-8 December 2015. 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 that after a progressive intensification of activity during the evening of 2 December, an eruption at Etna's Voragine Crater peaked between 0330 and 0410 on 3 December. During the peak period sustained lava fountains rose over 1 km above the crater with some jets of hot material rising 3 km high. An ash plume rose several kilometers high and drifted NE, causing ashfall in Linguaglossa, Francavilla di Sicilia, Milazzo, Messina, and Reggio Calabria. Activity had almost ceased by dawn. This event was among the largest in the last 20 years, similar to large events occurring at the same crater on 22 July 1998 and 4 September 1999.
At about 1000 on 4 December renewed activity at Voragine Crater was characterized by tall lava fountains and an ash plume that rose 7-8 km high. The ash plume had a mushrooming top and produced deposits of coarse-grained pyroclastic material on the upper SW flank above 2 km elevation. Ashfall was reported in Giarre-Zafferana Etnea on the E flank. The activity was accompanied by frequent ash emissions from a new pit crater that had recently opened on the upper E flank of the New Southeast Crater (NSEC) cone. Two more events occurred at Voragine Crater during 4-5 December, between 2130 and 2215 on 4 December and 1555 and 1635 on 5 December, again producing tall lava fountains and many-kilometer-high ash plumes.
During the evening of 5 December activity at Voragine Crater progressively diminished. Between 0300 and 0400 on 6 December surveillance cameras recorded the onset of vigorous Strombolian activity from the vent on the E flank of the NSEC cone. Repeated collapses of both old and new material from the cone's flank generated hot avalanches that traveled a few hundred meters E towards the Valle del Bove. Ongoing effusive activity through the day produced two lava flows; one advanced NE for less than 1 km and the other advanced E. Strombolian activity continued through the evening. On 7 December a second vent on the E part of NSEC was also active, and the main lava flow had advanced 4 km. During the early morning hours of 8 December Strombolian activity progressively diminished and then ended. Later that afternoon weak Strombolian activity and ash emission were observed at the Northeast Crater.
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.