STROMBOLI, 28-29 September 1995

Stromboli has shown a generally low level of activity during most of 1995 so far, much lower than it was in summer-autumn 1994. Visits by numerous persons in August to October revealed that eruptions occurred from several vents and produced either low lava fountains or ash plumes. The most regular activity occurred, as during recent years, from vent 3/1 in the NE part of crater C3, consisting of continuous night glow and frequent spatter ejections, at times projecting bombs outside the crater. Small ash and bomb explosions occurred from its southwestern neighbor, vent 3/2. The northeasternmost vent in the crater area, vent 1/1 in C1, had periods of vigorous lava fountaining, often dropping incandescent bombs on the upper part of the Sciara del Fuoco, particularly in early September. During dry weather, a very dense gas plume was always vis- ible above Stromboli, often forming a hazy layer at about 850-900 m altitude that extended for tens of kilometers away from the volcano.

A summit visit on 28-29 September by Giada Giuntoli and Boris Behncke was made in order to reveal changes to the crater morphology and eruptive behavior, but bad weather and very strong gas and steam emission from the craters seriously hampered the observations which therefore give only a sketchy impression of the state of the volcano at that time. The view of the craters from the summit was almost impossible because the vapor and gas plume was driven immediately above the viewing point at Pizzo sopra la Fossa by strong wind.

Craters 2 and 3 had not changed significantly since the last summit visit on 20 April. No active vents and no fumarolic activity were seen at night (when observations were at times possible) in C2, and vent 3/1 showed its usual fluctuating glow but no spatter ejections. Vent 3/2 had very weak emissions of reddish ash at intervals ranging from 5 to 20 minutes. The ash passively mixed with the dense vapor plume and did not pierce through it, pointing to the low energy of the emissions. No noise was heard during these emissions, but weak noises could have easily been masked by the stormy wind at Stromboli's summit.

Crater 1 had been largely filled with small spatter cones during the summer 1994 activity, but destruction of these cones began with a powerful phreatic explosion on 5 March 1995. That explosion opened a pit about 70 m in diameter and blew away half of the largest 1994 cone (at vent 1/2) and all of the smaller cones north and northeast of it (in the vent area 1/1). The remaining half of the cone at 1/2 has further collapsed since April 1995 and now forms a small rounded hump instead of the spine-like feature it was before. The "Gemelli" (twin) cones in vent area 1/3 remain standing. None of them has erupted after September/October 1994, but a new incandescent vent (about 10 m wide) has formed at the SE base of the southwestern twin cone. This vent was the site of brief noisy gas explosions that did not eject any rock fragments but a diffuse incandescent gas cloud.

The most vigorous eruptions during the observation period occurred from vent 1/1 which itself could not be observed. The eruptions ejected black ash plumes that rose vertically above the vapor plume, at times higher than 100 m, in spite of the wind, testifying the much higher energy of these eruptions with respect to those from vent 3/2. At dark, incandescent ejections were seen in some of these eruptions, and loud roaring noises were always audible. Such eruptions occurred at intervals ranging from 5 minutes to more than 1 hour.

Observations by more fortunate observers in early October disclosed continuing low-level activity with eruptions from vents 1/1 and 3/2 and incandescence from vents 1/3 and 3/1. Many of the eruptions produced ash plumes and were probably phreatomagmatic.

After the period of very intense activity in summer-autumn 1994, Stromboli presents itself at a very low level of activity since early 1995, lower probably than at any time since the last major effusive eruption in 1985-1986. The low level of visible activity is confirmed by the seismic data acquired by the University of Udine (see recent Bulletins) and has been interpreted as a possible precursor of a much more powerful eruption in the near future by several researchers, resulting in a warning and prohibition of access to the volcano in April-May. The alarm, although never officially lifted, has not been mentioned anymore during recent months, and people again croweded the summit during the summer nights.

BACK TO STROMBOLI IN1994

BACK TO STROMBOLI IN1995