Report on Etna (Italy) — July 1979
Scientific Event Alert Network Bulletin, vol. 4, no. 7 (July 1979)
Managing Editor: David Squires.
Etna (Italy) Eruption from summit and SE flank
Please cite this report as:
Global Volcanism Program, 1979. Report on Etna (Italy). In: Squires, D. (ed.), Scientific Event Alert Network Bulletin, 4:7. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN197907-211060.
37.748°N, 14.999°E; summit elev. 3295 m
All times are local (unless otherwise noted)
By early July, activity had resumed at the Chasm in Etna's central crater. The Chasm had been continuously active for many years but had become quiescent and largely filled with ash during the 1978 eruptions. John Guest and coworkers arrived at the volcano 11 July and observed small, sharp, strombolian explosions from a small pit that had formed in the floor of the Chasm. When visited again on 27 July, the pit was filled with lava, covered by a thin crust that swelled prior to frequent Strombolian explosions. The lava lake had grown further by the next day. Large blisters formed in the lake, then burst, throwing bombs 200 m or more high. Some fell 50-60 m outside the rim of the Chasm.
Bocca Nuova, adjacent to the Chasm, was quiet on 11 July. However, collapse activity deep in this crater could be heard 27 July, and billowing clouds of dust were emitted.
Guest and coworkers observed the beginning of activity at a third site during the morning of 16 July, when strong gas emission started from a vent at the bottom of one of the 1978 craters on the upper SE flank (figure 5). Ejection of lithic blocks and a little fresh magma soon commenced, with the proportion of juvenile material increasing steadily. By afternoon, strong strombolian activity was occurring from the vent. The next day, bombs from many of the spasmodic explosions rose 200-300 m above the rim of the (100-m deep) 1978 crater. Most bombs fell back inside the crater, but a few landed as much as 50 m outside the rim. Another vent, on the side of the 1978 crater, emitted ash, building a small conecone. Similar activity continued until the night of 22-23 July, when the explosions became stronger and more frequent. The stronger activity continued through the morning of the 23rd, then declined to the more moderate levels of 17-22 July. Six vents were active at various times, two of which were dominant. This activity persisted, with some fluctuations in intensity, through 28 July, when Guest and coworkers left the volcano.
After a series of felt earthquakes 29-30 July, strong explosions from the Chasm began during the night of 3-4 August. Heavy ashfall took place in Catania, closing the airport, and ash fell as far away as Syracusa, about 80 km to the SSE. Unusual lightning accompanied the explosions, which were visible from the mainland, 75 km from Etna. Two fissures opened early 4 August near crater l, at 2950 m and 2875 m altitude. By afternoon, fluid lava from these fissures had traveled 13 km down the E flank, threatening the village of Fornazzo and forcing its evacuation. However, about 300 m from Fornazzo the lava changed direction, and damage was limited to about 1,000 acres of fruit and nut orchards. By late 4 August, summit explosions had apparently ceased.
Several new fissures opened the next day. The first was 1 km long, located at 1,800 m altitude in the Valle del Bove, on the SE flank. Others opened later on the NE flank, producing lava that flowed down two valleys. Lava effusion from some of these vents was continuing as of the morning of 7 August.
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.
Information Contacts: J. Guest, J. Murray, Univ. of London; R. Romano, IIV; UPI; Reuters.