Report on Etna (Italy) — 13 February-19 February 2013
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 13 February-19 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, 13 February-19 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 that during the evenings of 13 and 14 February a camera recorded incandescence from Etna's New Southeast Crater (NSEC). In the early hours of 15 February incandescent bombs were ejected just higher than the crater rim. Strombolian activity gradually intensified on 17 February along with volcanic tremor amplitude. Small Strombolian explosions occurred every 1-2 seconds at daybreak, launching coarse-grained pyroclastic material a few tens of meters above the crater rim. After reaching a peak around 0700, activity started to diminish; a few hours later, the volcanic tremor amplitude returned to background levels, and by the evening there was no sign of eruptive activity.
Shortly before midnight on 18 February, the clouds dissipated from the summit area, revealing continuous weak Strombolian activity within NSEC. During 0000-0200 on 19 February the volcanic tremor amplitude rose gradually, then distinctly increased after 0200. Contemporaneously, the eruptive activity started to intensify from one vent in the center of the crater. About 10 minutes later, lava started to overflow through the deep notch in the SE crater rim, expanding slowly toward the steep W slope of the Valle del Bove. At 0457 the small pit crater that had formed on the SW rim of the NSEC on 27 August 2012 started to emit ash, and repeated rim collapses generated small landslides. Activity of the main vent within the crater rapidly increased, and at 0503 a lava fountain rose about 200 m above the summit of the cone.
During the interval from 0503 until 0507, several vents became active along a fracture from the pit crater to the notch in the SE crater rim. A dense cloud of ash rose and drifted E. Next, the entire NSEC cone was subjected to heavy fallout of coarse-grained pyroclastic material. The main lava flow advanced SE, and a small lava flow that developed on the flank below the pit crater traveled along the March 2012 fracture zone between the old and new SEC cones. At 0515 lava fountains rose 300-500 m above the crater rim and produced bombs and spatter that covered the S flank of the cone. Small avalanches of this incandescent material generated ash clouds. During 0516-0518 the S flank of the cone was veiled by a dense curtain of fallout from the lava fountains. At the same time, dense vapor clouds rose from the upper E flank of Etna, generated by the copious fallout of incandescent pyroclastic material onto the snow.
At 0519, a more substantial avalanche of fresh material detached from the S flank of the cone, generating a small pyroclastic flow that expanded a few hundred meters first S and then E. At 0536 a thermal monitoring camera recorded a lahar from near the Belvedere area, which was followed by a broad lava flow that descended the steep slope and reached the base after less than 20 minutes. During its descent, the lava continued to melt snow, producing numerous small lahars. At 0550 a second lava flow N of the first also generated lahars. Finally, at about 0600, a third lava flow, which generated a lahar, descended the W slope of the Valle del Bove to the S of the first flow.
Lava fountaining from the pit crater started to diminish around 0525, and at 0535 transitioned into ash emissions alternating with brief jets of incandescent lava. At 0545, one single vent, in the central portion of the NSEC, continued to produce lava fountains about 200 m high. A few minutes later, however, a new lava flow started to descend the lower SE flank of the cone, possibly after the opening of a new eruptive vent in the lower part of the notch cutting that sector of the cone. Surveillance cameras showed brief lava fountaining at that site, before all lava fountaining ceased shortly before 0600. During the interval between 0600 and 0615, the activity was characterized by emission of a dense ash plume with frequent jets of lava and powerful explosions, which launched large glowing bombs beyond the summit of the old Southeast Crater cone. After 0615 only ash emission persisted. At 0622 a puff of ash was emitted from the Bocca Nuova; shortly thereafter, ash emissions from the NSEC diminished notably and became discontinuous; the last, weak puffs of ash were observed around 0710. Slow lava emissions continued for a few more hours from the lowermost vent, which had opened shortly after 0547 on the SE flank of the cone. During the late afternoon of 19 February, small ash puffs were again emitted from the Bocca Nuova. Tephra fell in a narrow area extending from the NSEC towards the E, including Milo and Fornazzo (10 km E), Giarre (16 km E) and Riposto (18 km E).
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.