Report on Etna (Italy) — 20 February-26 February 2013
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 20 February-26 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, 20 February-26 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 two episodes of lava fountaining from Etna's New Southeast Crater (NSEC) on 20 February. The first episode's most energetic phase occurred during 0150-0235, producing an ash plume that drifted ESE, small lahars, lava flows from the fissure cutting the SE crater rim, and lava flows from a new eruptive fissure which opened on the lower SW flank of the cone. After the cessation of lava fountaining, weak spattering and low-rate lava emission continued from two small fissures at the SE base of the cone. During the late morning, eruptive activity at NSEC re-intensified. The second episode began just after 1415 and ended at about 1450. An ash cloud drifted E, and new lava flows traveled towards the Valle del Bove, following the paths of previous flows. Slow-moving lava flows from the fissures at the SE base of the NSEC continued into the next day, accompanied by sporadic, weak Strombolian explosions at the NSEC.
At 0233 on 21 February a new vent opened high on the W slope of the Valle del Bove and produced a lava flow that melted snow, creating lahars and voluminous steam plumes. At about 0300 Strombolian activity resumed at the NSEC; the activity became virtually continuous by 0440 and produced jets of incandescent lava that rose at most 100 m above the crater rim. Cloud cover periodically prevented observations, but at 0540 the clouds were illuminated, and at 0545 a lava flow emerged from the cloud cover. An ash plume drifted N, causing ashfall in the area between Randazzo (15 km NNE) and Linguaglossa (7 km NE), at Patti on the Tyrrhenian (N coast of Sicily), and as far as Lipari (more than 80 km N). Scoria clasts up to 15 cm in diameter also fell in Linguaglossa. After the cessation of this fourth paroxysm in just over two days, effusive activity continued from the eruptive vents, feeding two lava flows that traveled 2.5 km down to the base of the steep W slope of the Valle del Bove. This activity, accompanied by sporadic small Strombolian explosions at the NSEC, continued into the morning of 22 February.
At about 0700 on 22 February, rising tremor amplitude signaled the onset of a new episode, but from Bocca Nuova. Between 0730 and 0815 many vapor puffs and thermal anomalies were observed. Cloud cover prevented clear views, but mild Strombolian activity was likely occurring within the crater. At about 0815 the volcanic tremor amplitude started decreasing and the gas emissions from Bocca Nuova became less conspicuous. Contemporaneously, the emission of lava from the two effusive vents at the SE base of the NSEC cone and below the Belvedere station decreased and completely ceased during the afternoon of 22 February.
At about 1625 on 23 February thermal anomalies were detected from NSEC and 15 minutes later lava was visible from the vent at the SE base of the NSEC cone. By nightfall the lava flow and Strombolian activity were visible from populated areas on the S and E flanks, although cloud cover hampered views. Activity intensified during 1900-1930; lava fountains rose at most 150 m above the crater rim and a well-fed lava flow spilled through the breach in the SE crater rim and traveled toward the W slope of the Valle del Bove. Within the next 10 minutes jets of lava rose 500-800 m above the rim. During that time, the emission of pyroclastic material increased dramatically, forming a dense plume that drifted NE; the entire NE flank, from the NSEC to Pizzi Deneri and beyond, was covered with a sheet of incandescent material. Eyewitnesses also reported the fall of large clasts, some incandescent, in the area of Monte Baracca, ~5 km NE of the NSEC. High lava fountaining continued for about 35 minutes. At 2014 the height of the lava fountains rapidly decreased, and two minutes later, the activity had changed to Strombolian explosions that ejected incandescent tephra up to 100 m above the crater rim. At 2030 all explosive activity was essentially over. During the morning of 24 February, the lava flow emitted from NSEC continued to be fed, probably by one or more vents near Belvedere.
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.