Report on Etna (Italy) — 20 November-26 November 2002
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 20 November-26 November 2002
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2002. Report on Etna (Italy). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 20 November-26 November 2002. Smithsonian Institution and US Geological Survey.
37.748°N, 14.999°E; summit elev. 3295 m
All times are local (unless otherwise noted)
The 2002 Mt. Etna flank eruption that began on 27th October is continuing, after almost a month of activity. During this period several distinct phases of eruptive style have been observed. The first phase of the eruption ended on 5th November, when lava flows from the northern fissure stopped. Strombolian and fire-fountaining activity continued at the southern fissure, localised within the 2750 m elevation cinder cone that formed during early November. Lava jets reached heights of over 300 m above the crater, forming an ash column that spread mostly N, due to the strong wind, and reached an elevation of 4.7 km a.s.l..
The second phase of activity started on 12th November, when strong jets and continuous emission of ash gave way suddenly to mild Strombolian activity. Lava flows began to spread SW from the 2750 m vent on the 13th November. These flows ran parallel to the October flows towards Monte Nero and achieved a maximum length of 4 km on 19th November, stopping just 300 m before Casa Santa Barbara, at 1770 m a.s.l.. Lava output from the main vent then declined, and overflows covered the previous flow channel. As of 25th November the most advanced active flow fronts were located within 1 km from the vent.
Between 20 and 21st November another new vent opened on the SSE base of the 2750 m cinder cone. This vent produced a new lava flow that spread south towards Rifugio Sapienza. The flow length reached 1.9 km on the 22nd, and 2.7 km on the 23rd, covering the Rifugio K. The Rifugio Sapienza was threatened by the flow, and Civil Protection soon built up two earth barriers to divert the lava towards the east of buildings, as in the 2001 eruption. This diversion was once again successful, and the flow eventually stopped on 24th, a few metres before reaching the SP92 road connecting Zafferana to Rifugio Sapienza, after having traveled 3.6 km from the main vent.
Early on the 25th November, two new explosive vents opened to the N and SSE of the 2750 m cinder cone. This caused a shift in explosive activity from the crater of the previous cone to the newly formed vents, which produced fire fountaining activity and an ash plume rising to 4.7 km elevation and spreading north. Immediately afterwards the effusion rate of the south lava flow (towards Rifugio Sapienza) significantly decreased, and slightly increased in the southwest flow (towards Casa Santa Barbara). This caused new overflows above the previous flow channel on the lava flows directed to Casa Santa Barbara. The low effusion rate did not allow these flows to reach previous flow lengths, and they were less than 1 km long when last observed on 25th November. Observation of the flow field was impossible on the 26 November due to poor weather conditions.
SO2 emission from the volcano is still very high and fluctuating, keeping within the range of 20,000 to 7,000 tons per day. Taken together, the high amount of gas released by the volcano, the still high volcanic tremor, and the explosive activity still ongoing at the south vent, rather suggest that the eruption may continue for some time.
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.