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Report on Etna (Italy) — July 1994

Bulletin of the Global Volcanism Network, vol. 19, no. 7 (July 1994)
Managing Editor: Richard Wunderman.

Etna (Italy) Explosive degassing from La Voragine; fumarole temperatures reported

Please cite this report as:

Global Volcanism Program, 1994. Report on Etna (Italy). In: Wunderman, R (ed.), Bulletin of the Global Volcanism Network, 19:7. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199407-211060.

Volcano Profile |  Complete Bulletin


Etna

Italy

37.748°N, 14.999°E; summit elev. 3295 m

All times are local (unless otherwise noted)


The following describes [fieldwork] on 1-27 June and 10-18 July 1994.

"As during visits in June-July and September-October 1993, Northeast Crater was blocked and inactive, but collapse was continuing around the edge with minor rockfalls every few minutes or so. Southeast Crater was also little changed from 1993, with a quietly degassing vent under the SE rim, but no indication of gas coming out under pressure. There was strong high-temperature fumarolic activity around the crater rim, temperatures being generally highest in the cracks.

"The Chasm (La Voragine) had a single vent in its floor measuring ~ 8 x 10 m, discharging gas continuously under pressure in rhythmic puffs at a rate of ~ 30 puffs/min. On 17 June and 12 July only, distinct explosions could be heard at the rate of 1-8/min. These were the first signs of explosive activity since the end of the 1991-93 eruption, and an indication that the Strombolian degassing that has characterized the summit over the past few hundred years is resuming.

"Bocca Nuova vent was degassing almost totally silently from two vents, one to the SE and one to the W; however, on 27 June when the weather was calm, 13 very faint gas puffs/min could be heard. The SE vent seemed similar to last year, measuring ~ 10 m in diameter, but the W vent had collapsed and enlarged considerably, now measuring perhaps as much as 50 m in diameter. On the early morning of 16 June a reddish tinge to the plume above Bocca Nuova was first noticed. Upon closer inspection on 17 June, the SE vent was seen to be pouring out thick clouds of red dust, apparently a result of internal collapse within the vent, while the W vent continued to emit white fume only. Dust emission intensified in the following days, causing the downwind side (S through W) of the summit to become a striking red color. The activity was continuing in mid-July.

"The levelling traverse showed comparatively small vertical movements since September 1993. The area near Belvedere, and other areas over the dyke intruded during the 1991-93 eruption, had subsided by up to 2 cm, as had the NE rift zone near Monte Pizzillo. During the same period, a small area ~1 km SW of the summit inflated by just over 1 cm. Horizontal movements measured since October 1993 showed generally small or insignificant changes, with nearly all lines recording changes of >1 cm. Only two stations appear to have moved by more than this; a station on the E edge of Southeast Crater had shifted 3 cm E relative to nearby stations, and a station close to the NW edge of the Bocca Nuova had moved 2 cm W. These movements are consistent with expansion of the central magma column as it refills.

"Surface temperatures were measured between 1 and 27 June at four active fumarole areas with a Minolta/Land Cyclops Compac 3 hand-held radiometer (8-14 mm). Temperatures were not corrected for spectral emissivity, so all radiant temperatures are given here as brightness temperatures. On the NE rift zone, nine areas of fumaroles were observed near the N edge of the 1966-67 lavas (between 2,450 and 2,500 m altitude). Temperatures for fumaroles at the two lowest of these areas ranged between 33 and 50°C. Another area of fumaroles observed at the upper rim of the W wall of the Valle del Bove around Belvedere, above the 1991-93 dyke, had temperatures in the 57.5-84.7°C range. Temperatures measured at fumaroles and cracks in the still-cooling 1991-93 lava-flow field in the Valle del Bove were between 85 and 221°C. The locations and temperatures of fumarole areas measured in the vicinity of the summit craters are given in table 5. Temperatures of the vents within the central craters were also measured from the crater rim: 342°C for the Chasm vent, and 159 and 81.5°C, respectively, for the SE and W vents of Bocca Nuova. Active fumaroles were observed, but not measured, along the 1991-93 fissure zone and 14 December 1991 cones and flows between Southeast Crater and Belvedere, along the October 1986 fissure zone, and in the Valle del Bove below Monte Simone."

Table 5. Fumarole temperatures in the vicinity of Etna's summit craters, measured on 18 and 27 June, and 14 October 1994. Courtesy of Andrew Harris, Open University.

Date Fumarole / Rift Locations Temperature (°C)
27 Jun 1994 NE Crater - at N rim 50.4-65.0
27 Jun 1994 NE Crater - rifts at NW rim 56.0-141
27 Jun 1994 NE Crater - at dip in NW rim 45.5-97.4
27 Jun 1994 NE Crater - at E rim 51.4-85.6
18 Jun 1994 Bocca Nuova - on N slope 40.5-75.6
18, 27 Jun 1994 Bocca Nuova - inside N rim 42.2-54.3
27 Jun 1994 Bocca Nuova - rifts at N rim 52.0-74.4
18 Jun 1994 Bocca Nuova - at SW rim 52.0-65.7
18, 27 Jun 1994 Central Craters - at S rim 40.6-82.6
27 Jun 1994 Between central and SE Craters 59.1-81.3
18, 27 Jun 1994 SE Crater - rifts and fumarole at N rim 51.2-312
27 Jun 1994 SE Crater - rifts and fumarole at W rim 60.0-208
14 Oct 1994 NE Crater - fumarole at N rim 39.2-77.4
14 Oct 1994 NE Crater - rifts at NW rim 153-246
14 Oct 1994 NE Crater - fumarole at W flank 50.4-74.2
14 Oct 1994 NE Crater - fumarole at W rim 41.0-210
14 Oct 1994 NE Crater - fumarole at S rim 50.5-221
14 Oct 1994 Bocca Nuova - fumarole at N flank 50.1-75.5
14 Oct 1994 Bocca Nuova - rifts and fumarole at N rim 47.3-74.5
14 Oct 1994 Bocca Nuova - fumarole at SW rim 50.0-72.4
14 Oct 1994 Central Craters - fumarole at S rim 49.2-82.4
14 Oct 1994 Fumarole between central and SE craters 50.2-82.8
14 Oct 1994 SE Crater - rifts and fumarole at N rim 57.5-482
14 Oct 1994 SE Crater - rifts and fumarole at NW rim 56.4-218
14 Oct 1994 SE Crater - rifts and fumarole at W rim 46.8-99.5
14 Oct 1994 SE Crater - rifts and fumarole at S rim 49.9-88.0
14 Oct 1994 SE Crater - rifts and fumarole at E rim 68.5-180
14 Oct 1994 SE Crater - rifts and fumarole at NE rim 52.2-121

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. Murray and A. Harris, Open Univ; L. Platt, Sheffield Univ; D. Renouf, UK.