Report on Etna (Italy) — 6 April-12 April 2011
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 6 April-12 April 2011
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2011. Report on Etna (Italy). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 6 April-12 April 2011. Smithsonian Institution and US Geological Survey.
37.748°N, 14.999°E; summit elev. 3295 m
All times are local (unless otherwise noted)
INGV-CT reported that from 29 March through the first few days of April, a series of gas-and-ash emissions, rarely with minor incandescent material, rose from the pit crater on the E flank of Etna's SE Crater cone. On 8 April small Strombolian explosions occurred from two vents located in the W portion of the crater floor; ejecta were confined to the crater depression. On 9 April seismicity from the Strombolian activity increased throughout the day. In the afternoon, explosive activity commenced from two vents before lava flows covered the crater floor. Later that evening incandescent blocks appeared within a breach in the E rim of the crater, followed by a small overflow of lava. The lava flow advanced from the base of the SE Crater cone toward the W headwall of the Valle del Bove, as far as 1 km. At the same time small but frequent Strombolian explosions continued within the crater.
During the night of 9-10 April, the Strombolian activity within the pit crater gradually increased, as well as volcanic tremor amplitude. The lava flow continued to advance. On 10 April, activity and tremor amplitude significantly increased and culminated with vigorous lava fountaining. An ash-and-gas plume drifted SE, causing ashfall in areas downwind. The lava-flow emission rate also increased dramatically. A second lava flow covered the first and traveled down into the Valle del Bove, essentially following the same path as the lava flows of 12-13 January and 18 February. The lava flow encountered thick snow cover, leading to violent explosive interactions that generated pyroclastic flows, and resulted in spectacular vapor-and-ash plumes. The eruption declined rapidly after about 1500; no activity was observed later than the afternoon.
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.