Report on Etna (Italy) — August 1977
Natural Science Event Bulletin, vol. 2, no. 8 (August 1977)
Managing Editor: David Squires.
Etna (Italy) Two eruptions in August generate fountaining and lava flows
Please cite this report as:
Global Volcanism Program, 1977. Report on Etna (Italy) (Squires, D., ed.). Natural Science Event Bulletin, 2:8. Smithsonian Institution. https://doi.org/10.5479/si.GVP.NSEB197708-211060.
37.748°N, 14.999°E; summit elev. 3320 m
All times are local (unless otherwise noted)
"After a period of quiescence since the beginning of this year, Etna erupted again on 16 July. New explosive and effusive boccas opened on the lower flank of the Northeast Crater cone at an altitude of 3,200-3,270 m. The first signs of eruption occurred in early July when a small pit opened on the N edge of the Northeast Crater Cone. Initially this pit emitted high-temperature gas which during the night was seen to be incandescent.
"The first sign of lava emission was seen by a guide at 0400 on 16 July when he observed a small 'lake' of lava in the bottom of the pit. An hour later weak explosive activity started and increased to become stable at about 15 explosions/minute by 1000. Incandescent material was thrown 300 m above the vent, with a maximum height of 500 m. The maximum range of the bombs was 400-500 m. During this early period of explosive activity, a fracture opened at about 3,240 m on the lower slopes of the cone and flows were emitted from the end of the fracture (at 3,220 m), first towards the NE and later to the E. At the same time ephemeral boccas (3,200 m) opened below the main fracture and fed a small flow in a northerly direction. Explosive activity reached its peak during the night of 17 July. During the early hours of 18 July collapse occurred in the Northeast Crater itself, causing great clouds of dust and ash. The explosive activity at the new vent then diminished both in frequency and intensity, becoming extreme1y variable.
"On 18 July the flows had reached a length of 800 m to the N and 2 km to the E. From then onwards the explosive activity continued to diminish, as did the effusion of lava to the N flow. The E flow reached the edge of Valle del Leone and continued as the principal flow, reaching a total length of 4 km by the end of the eruption. The N flow stopped with a total length of 1 km. Explosive activity ended at 1000 on 22 July and the lava flows stopped in the late afternoon.
"The area covered by lava was 0.16 km2, the volume of lava was 4.8 x 105 m3 and volume of pyroclastic material 500 m3. Microseismic activity was noted before and during the eruption.
"The Northeast Crater started erupting again on 5 August at 1430. The activity began with strong explosions from the July vent, with lava fountains being thrown to 400 m in the early stages. One lava flow formed, advancing N from a fracture on the N slope of the Northeast Crater Cone. The fracture was oriented approximately NNE. The lava was fluid and traveled about 3 km. Seismic activity was observed just before and during the eruption, which ended at 0630 on 6 August."
UPI reported that a third eruption began early 14 August and lasted only 14 hours. Fountains or strombolian ejecta rose 200 m above the vent, and two lava flows, each about 200 m wide, moved about 4 km down 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.
Information Contacts: R. Romano, G. Frazzetta, and D. Condarelli, IIV; J. Guest, Univ. of London; UPI.