Report on Etna (Italy) — February 1997
Bulletin of the Global Volcanism Network, vol. 22, no. 2 (February 1997)
Managing Editor: Richard Wunderman.
Etna (Italy) Summary of activity since November 1996
Please cite this report as:
Global Volcanism Program, 1997. Report on Etna (Italy). In: Wunderman, R (ed.), Bulletin of the Global Volcanism Network, 22:2. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199702-211060.
37.748°N, 14.999°E; summit elev. 3295 m
All times are local (unless otherwise noted)
The following summarizes the activity observed at Etna from November 1996 through March 1997.
Activity during November 1996. On 2 November both Bocca Nuova (BN) and Northeast Crater (NEC) produced Strombolian activity lasting all night. On 6 November an old degassing vent on the inner wall on the SE side of the crater emitted one ash puff that reached 1 km in height. The associated explosion enlarged the vent and caused debris from the inner walls to cover a wide portion of the S crater bottom. A few small lava blocks fell on the S crater rim and a brown, totally non-juvenile ash deposit covered the E sector of Etna's summit a few kilometers down from the crater. The same day Southeast Crater (SEC), quiet since Autumn 1991, began very low Strombolian activity from two vents on its floor. During the evening of 6 November glow was seen above the SEC, but in the following days eruptive activity remained very low.
Overflights on 5-7 November confirmed that Strombolian activity occurred at BN almost continuously from one or more closely spaced vents on the intracrater cone. Besides almost continuous ash puffs produced on 10 and 11 November at BN, there were two large ash explosions on 16 and 18 November.
The surveillance video camera captured intervals of night glows over NEC (from 0110 to 0130 on 23 November; from 1812 to 2100 on 24 November; and for a half-hour during the night of 27-28 November). At SEC between 23 and 28 November weak Strombolian activity occurred sporadically. BN produced several discrete Strombolian explosions from 2005 to 2140 on 28 November.
Activity during December 1996. The summit craters erupted infrequently in the first half of December and more frequently in the second half. On 15 December Strombolian activity was reported at both craters during 2340-0200. At NEC episodes of Strombolian activity occurred on 17 December (1730-2140), 18 December (0150-0438, 1830-0045), 19 December (1740-1747, 2125-2215), and 21 December (0400-0540, 1730-1800).
During the morning of 16 December some ash explosions occurred at BN; in the morning of 19 December there was both an ash plume and ash puffs. A small wall collapsed on 21 December at BN's S vent adding particulate to the summit plume.
Between 22 and 24 December some short periods of Strombolian activity were recorded at both NEC and BN. At SEC during December there were no available video records; however, direct observations revealed only very weak and discontinuous activity.
Activity during January 1997. BN's Strombolian activity was reported at multiple times: 1800-2100 on 7 January; 2348-0102 beginning on 9 January; during several ~1-hour intervals, 11-13 January; and as weak, continuous activity, 14-24 January. More episodes occurred at 1940-2130 on 27 January; at 0800- 1400 on 29 January; at 0800-0900 on 30 January; and at 0400-0500 on 31 January.
NEC's Strombolian activity took place at these times: 2000-2100 on 7 January; several ~1-hour episodes between 11-13 January; and sporadic weak episodes, 20-22 January. Later, from 25 January until the end of the month, the eruptive vigor rose; ash emissions occurred during 0800-1400 on 29 January and eruptions could be watched from a distance from sunset until 2200 on 30 January.
On 25 January, at 1920 SEC began one hour of very weak Strombolian activity. The activity of SEC had formed a small cinder cone inside the crater and some short fan-shaped aa lava flows departing from the cone.
Activity during February-5 March 1997. The first half of February was characterized by the continuous emission of ash from BN; bomb and lapilli ejections inside the crater were reported on 11 February. There was strong degassing from NEC but weak emissions from Voragine Crater. Inside SEC the small cinder cone spattered continuously, though weakly. During the second half of February both BN and NEC plumes frequently contained ash.
A field survey on 5 March revealed that some cinder cones formed in BN. One of these cones threw bombs up to the crater rim and a vent in the SE part of the crater gave off strong emissions of gas and red ash. Fresh lava tongues were identified on 5 March at the W edge of the SEC cinder cone. A later image of SEC (11 March) is shown in figure 65. Voragine crater only degassed whereas NEC collapsed slightly as indicated by minor debris in the crater.
|Figure 65. Aerial view of SEC on 11 March 1997 showing the intracrater cinder cone and the small lava flow first seen on 5 March. Photo by A. Amantia; provided courtesy of CNR-Istituto Internazionale di Vulcanologia.|
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: Mauro Coltelli and Paola Del Carlo, CNR Istituto Internazionale di Vulcanologia, Piazza Roma 2, Catania, Italy (URL: http://www.ingv.it/en/).