Report on Etna (Italy) — 18 July-24 July 2001
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 18 July-24 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, 18 July-24 July 2001. Smithsonian Institution and US Geological Survey.
37.748°N, 14.999°E; summit elev. 3295 m
All times are local (unless otherwise noted)
A large flank eruption began on 17 July at Etna and produced several lava flows that were emitted from four new fissures and strong explosive activity at a fifth. Four of the fissures were on the SE flank, and the fifth was on the NE flank. There were fears that lava flows from two of the fissures would reach the town of Nicolosi (~15 km SSE of the volcano) and a nearby popular tourist area. According to the Italy's Volcanoes website, the 17th eruptive episode in 2001 began on the morning of 17 July and a few hours later a new eruptive fissure opened at the S base of the Southeast Crater cone (see map of fissure locations). Mild Strombolian activity occurred from the fissure and a lava flow extended SSE. During the evening of the 17th a second eruptive fissure emitted an extensive lava flow that spread SE toward the Valle del Bove rim. On 18 July at about 0200 a seismic swarm was accompanied by the opening of a third eruptive fissure at about 2,100 m elevation. Mild Strombolian activity and a sluggish lava flow traveled toward the S. Later in the day the lava flow crossed the main access road to the S flank of Etna and headed towards Nicolosi. A spectator was seriously injured when he fell while trying to avoid projectiles.
On the evening of 18 July the fourth eruptive vent since the episode began opened near 2,700 m elevation on the SE flank. The main explosive activity occurred at this vent, including powerful Strombolian blasts that sent incandescent volcanic bombs as high as 200 m and produced ash columns that rose several kilometers. Lava from this vent progressed towards the tourist complex around the Rifugio Sapienza. On 20 July around 1100 a fifth eruptive fissure became active, but unlike the other fissures it was on the NE flank in the Valle de Leone. Lava emitted from this fissure flowed SE.
By 22 July the lava flow from the third fissure was 4 km away from Nicolosi, but it was advancing very slowly over nearly flat terrain and appeared to have stopped by the next day. Earth barriers were created in an attempt to divert lava from the tourist complex that had already been damaged by volcanic bombs. Continuous ashfall occurred near the explosive fourth vent. The entire area between the towns of Giarre (~17 km E of the volcano) and Catania (~25 km SSE of the volcano) was covered by a thin layer of ash; there was an especially large amount of ash in Catania. The Fontanarossa International Airport of Catania was closed on 22 July and again the next day due to ashfall.
The Toulouse VAAC reported that the new Etna Sistema Poseidon webcam showed ash emission starting on 20 July. The previous webcam had been damaged by earthquakes near the start of the eruption. SE-drifting ash clouds were detected several times on satellite imagery. An ash cloud was reported to have reached a maximum height of ~5.2 km on 22 July. According to news reports, a state of emergency was declared for the area near Etna on 20 July. As of 24 July the eruption was continuing.
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.