Report on Etna (Italy) — 25 April-1 May 2012
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 25 April-1 May 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, 25 April-1 May 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 twenty-fifth paroxysmal eruptive episode since January 2011 took place at New SE Crater (New SEC) of Etna during the morning of 24 April following about 11 days of quiescence. During 21-22 April a series of small ash emissions observed by web cameras drifted downslope to the E. On 22 April prolonged emissions of white vapor rose from an area in the upper portion of the fissure that cuts the SE flank of the cone. At night several incandescent spots were visible on the NE and S crater rims, where hot gas heated the surrounding rocks. On 23 April a small thermal anomaly in the area of New SE Crater was produced by a tiny lava flow, which issued from the same vent that had produced the prolonged vapor emissions on the previous day. The lava flow slowly advanced a few hundred meters toward the Valle del Bove, but stagnated on the W rim. Another lava flow was produced later that day.
At around 1800 the effusive vent started to vigorously spatter. A second vent became active a few tens of meters further upslope, which initially ejected spatter, but activity rapidly evolved into frequent Strombolian explosions accompanied by a slow rise in the volcanic tremor amplitude. During the following hours, sporadic explosions were also observed from a vent located within the New SEC; the activity remained more or less consistent, while the volcanic tremor amplitude fluctuated at only slightly elevated levels. At 0210 0n 24 April the Strombolian activity showed a marked increase and turned into sustained lava fountaining at 0230. A plume with a heavy load of ash and lapilli rose a few kilometers, drifted NE, and produced ashfall 15-17 km NE in Linguaglossa, Piedimonte, and Presa. The upper part of the plume drifted E and produced pea-sized lapilli fall in the area between Fornazzo (10 km E) and Giarre (17 km E). The phase of most intense lava fountaining lasted approximately 25 minutes, from 0240 until 0305 on 24 April, after which the intensity rapidly decreased and returned to Strombolian activity, before ceasing completely around 0340.
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.