Report on Etna (Italy) — 8 September-14 September 2004
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 8 September-14 September 2004
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2004. Report on Etna (Italy). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 8 September-14 September 2004. 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 at about 1030 on 7 September an effusive eruption began at Etna's summit. An approximately 230-m-long fissure opened at the base of Southeast Crater without any significant accompanying seismicity. Lava flowed from the base of the fissure, spreading SE towards the Valle del Bove. After 2 days of slow expansion of the field of fractures, between 0600 and 0700 on 10 September a new effusive vent opened at 2,650-m elevation on the upper western flank of the Valle del Bove. A lava flow poured out from this vent towards the E, spreading on the upper wall of the Valle del Bove. No explosive activity accompanied the emission of lava, but some phreatic explosions were triggered by lava flowing on a thick layer of snow. By 0930 the longest branch of the lava flow was 300 m long and 50 m wide. On the afternoon of 13 September, another effusive vent opened within the Valle del Bove, at about 2,200-m elevation, about 500 m SE of the previous vent. A lava flow from this vent spread in the valley at low output rate, while the previous flow from the vent at 2,650 m continued to feed a 1-km long lava flow. No lava flows threatened villages; the closest lava flow was at least 10 km from the nearest village.
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.