Report on Etna (Italy) — 29 February-6 March 2012
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 29 February-6 March 2012
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2012. Report on Etna (Italy). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 29 February-6 March 2012. 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 third episode of lava fountaining from Etna's New Southeast Crater (New SEC) occurred on the morning of 4 March and was more explosive than the preceding episode. The beginning of the eruption was characterized by a rapid increase in volcanic tremor amplitude coincident with Strombolian explosions that increased in intensity and frequency. Just after 0800 lava overflowed the deep breach in the SE rim of the crater and reached the SE base of the cone within 15 minutes, then advanced towards the W rim of the Valle del Bove. Explosive activity changed to continuous lava fountaining and an eruption plume developed at about 0830. Large pyroclasts fell on the steep flanks of the cone, causing avalanches.
At about 0850 small pyroclastic flows generated by the partial collapse of the eruption column mainly descended the NE flank, and somewhat down the S flank. A lava flow was emitted from a new eruptive vent on the upper SW flank of the New SEC cone and descended into the saddle between the old and new SEC cones. The lava interacted with snow, causing powerful explosions and small pyroclastic flows. These phreatic explosions generated jets of vapor and launched rock fragments to distances of several tens of meters. A lahar developed which traveled toward the "Belvedere" monitoring station, on the W rim of the Valle del Bove, and passed a few tens of meters to the N of the monitoring instruments.
A lava flow also issued from an eruptive fissure on the upper N flank of the cone and descended a few hundred meters to the NE, surrounding the N base of the cone. After descending the steep W slope of the Valle del Bove, the flow split into several branches on the more gently sloping terrain. These branches exceeded in length those of 9 February, reaching a total distance of about 3.5 km from the crater. Shortly after 1000, the activity started to diminish; lava fountaining ceased at 1032, two hours after the onset of the paroxysmal phase. The lava flow emitted from the fissure on the SW flank of the cone continued advancing for a few hours after the cessation of the activity.
The eruption column rose several kilometers above the summit of Etna. Ash and lapilli were carried NE by the wind, affecting the areas around Piedimonte, Etneo, and Taormina. Fine ash fell as far as the Messina area and southern Calabria. Again, the pyroclastic cone of the New SEC had grown in height, mainly on its N rim.
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.