Report on Etna (Italy) — 25 July-31 July 2001
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 25 July-31 July 2001
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2001. Report on Etna (Italy). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 25 July-31 July 2001. Smithsonian Institution and US Geological Survey.
37.748°N, 14.999°E; summit elev. 3320 m
All times are local (unless otherwise noted)
During 25-31 July the eruption that began on 17 July at Etna's Southeast Crater continued at the same five eruptive fissures as the previous week. One of the fissures was located on the NE flank and the other four on the S flank at elevations of 2,950, 2,700, 2,500, and 2,100 m. During 24-26 July eruptive activity declined at the 2,100 m fissure, but then intensified on 27 July to reach the original level of Strombolian activity on the evening of 28 July. On 26 July modest lava emission occurred at the NE-flank fissure. At the 2,500 m fissure, where the strongest explosive activity occurred, a change was noted from the mostly phreatomagmatic eruptions that were prominent during the previous week to more violent Strombolian explosions and lava effusion. After lava began to flow from the 2,500 m fissure on 25 July, a pyroclastic cone began to grow around three of the vents and by 30 July the cone was ~100 m high. At the 2,950 m fissure (near the base of Southeast Crater) and 2,700 m fissure lava emission and mild explosive activity continued.
On 26 July lava from the 2,500 m elevation fissure continued to flow towards Rifugio Sapienza tourist complex, and as of 31 July a cable car base station and a small tourist shop had been destroyed by lava that surpassed constructed earth barriers. Lava continued to flow from the lower vents of the 2,100 m fissure in the direction of the town of Nicolosi (~15 km SSE of the volcano), but it was no longer considered a significant threat to the town. Near-continuous ashfall occurred S of the volcano, including in the town of Catania, ~25 km SSE of the volcano. The international Fontanarossa airport in Catania was closed repeatedly on 29 and 30 July due to ash on the runways. The Toulouse VAAC reported that ash clouds were occasionally visible on the Sistema Poseidon web cam and satellite imagery, with the highest cloud rising ~5.5 km above the volcano.
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.