Italy's Volcanoes: The Cradle of Volcanology

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Activity from 1985 to 1995:
A decade in the history of Stromboli

Part 2: The story in detail - 1989-1991

Eruption from vent 1 in Crater 1 on the morning of 17 September 1989.

Vent 2 within Crater 3 is seen here in eruption. Lava fountains were obliquely projected onto the S rim of the crater.

The activity in late March and early April 1990 was slightly more vigorous than in September 1989. The most striking difference was the frequent occurrence of dense ash plumes during the eruptions of vent area 3/2. Eruptions from this site were most frequent while those of 1/1 occurred about once or twice per hour. Very loud gas emissions with the ejection of few bombs occurred from 1/3; the bombs probably were rock fragments torn from the conduit walls by the violent gas outrush. No activity was noted at crater 2. Vent area 3/1 had active lava at depth, as could be stated from the characteristic sound audible at Pizzo sopra la Fossa.

I accessed the crater terrace shortly before and during sunset and had spectacular views of the features inside Craters 3 and 1. Vent area 3/2 had just had an eruption and incandescent bombs were still lying in it when I climbed to Crater 3's south rim. When darkness fell, three more or less circular pits each 3-5 m in diameter became well visible at vent area 3/1. They all contained brightly incandescent lava at depth which apparently was actively boiling, causing a fluctuating glow. No spatter ejections took place.

The view into Crater 1 was even more surprising. Two small cones were visible on its floor, each about 20 m high. Vent area 1/1 apparently had not developed a cone and appeared a gaping hole behind the regularly formed central cone at 1/2. This cone did not erupt during the entire visit to the summit and craters but an enchanting glow was visible within its 5-m-wide summit crater. On the left (southwestern) base of the cone there was a small hornito, merely a bocca with an elevated, ring-shaped rim. This vent only emitted steam and did not glow, nor did it erupt.

Crater 1 seen from the northeast on the afternoon of 1 April 1990. A small conelet, about 20 m high, is visible at vent area 1/3.

Spatter cone at vent area 1/2 (center of Crater 1) on the evening of 1 April 1990, viewed from the southeastern rim of the crater, about 30-50 m distant. The vent of this cone showed a suggestive glow but did not erupt.

Conelet at vent location 1/3, with eccentrically placed bocca at its southern base. No distinct summit bocca is recognizable.

Maybe the strangest feature within Crater 1 was a cone at vent area 1/3 which maybe had an extinct vent at its summit (I did not really recognize one), and an active bocca on its southern base. This eccentric vent, less than 5 m wide, was the site of occasional loud gas emissions, and between eruptions, was incandescent like the vent on the neighboring cone.

I left the crater terrace after about 30 minutes of observation. Several hours later, eruptions from 3/2 became much stronger and dropped abundant bombs on the area where I had stayed longest during my crater visit and taken photographs of the incandescent boccas at 3/1 and of the cones in Crater 1. The strong wind and low temperatures at night forced me to descend during darkness for the first time. It is possible, but it is very little pleasure! If you ever happen to do it, don't take the route on the back side of the volcano. I don't like it at daylight, at night it must be horrendous.

The first of several periods of highly increased explosive activity began during the summer of 1990 and reached its culmination in October of that year. According to a report in the GVN Bulletin, this was the strongest activity at Stromboli since 25 years.

I watched the activity on 7-8 November and found it most impressive, even though the climax had already passed. Although the summit was covered with dense steam clouds and observation of the craters from Pizzo sopra la Fossa was extremely difficult, it could be stated that many vents were active, most within Crater 1, and there were several periods of continuous activity that lasted up to 2 hours. Often, up to three vents erupted simultaneously. Still, each one had a very distinct manner of eruption. The northeasternmost one in Crater 1 did not participate in the periods of continuous activity but produced distinct blasts every 2-10 minutes, often accompanied by cannon-shot like bangs. A small vent in its vicinity emitted gas at very high pressure, causing a tremendous roaring sound similar to a jet engine, during a period of at least two hours.

After nightfall, occasional glimpses of the crater terrace could be made from Pizzo sopra la Fossa. The craters appeared largely filled with material that had accumulated since my last visit in early April 1990, and vent 1 in Crater 3 (where there had been three small lava ponds 7 months earlier) was now plainly visible, being no more than two small boccas that ejected tiny oblique jets of lava. Eruptions from vent 2 in Crater 3 were more rare but very powerful. At 2000, this vent and another one in Crater 1 erupted violently at the same time, followed by another powerful eruption from another vent in Crater 1. The entire crater terrace was covered with a sheet of incandescent bombs, and for a moment, all the gas and vapor had been blown away. There was a wide area having countless yellow-orange dots through which three vents blasted their continuous low fountains of liquid spatter. I was alone on the summit, there was the full moon rising in my back, and I was screaming! In the distance, the lights of Calabria and Sicily were flickering, there was lightning from a distant thunderstorm (which fortunately did not arrive at Stromboli), and countless stars dotted the sky...

Panoramic view of the crater terrace seen from Pizzo sopra la Fossa on 29 August 1991. Note filling of craters with pyroclastics and small cone at vent area 3/1 (in center of image).

During the months following, normal conditions prevailed at Stromboli. I saw it again on 29 August 1991 (together with Jon Dehn), during a period of very reduced activity which allowed a descent to the craters and observation of the activity inside Crater 3. A small cone was present at the site of vent 1, and incandescence was visible even during daylight in two openings on the sides of the cone. Vent 2, in the SW part of Crater 1, erupted frequently. During the night of 29-30 August, lava fountains from this vent had risen about 100 m high, but on the morning, while we stayed on the crater rim, they were much lower, barely reaching the crater rim which was maybe 50 m above the crater floor.

We noted that between the eruptions the vent was buried under material that had slid from the inner crater walls. Eruptions usually first fragmented some of the scoria over the vent before fresh lava sprayed up, thus producing diffuse ash plumes mixed with glowing lava fragments. Virtually all of this material fell back into the crater, causing small avalanches that buried the vent within seconds after an eruption.

Very noisy explosions occurred about twice per hour from a vent at the NE end of Crater 1, preventing us from approaching that crater. We were nonetheless able to observe a small, very regularly shaped cone at the southwesternmost vent in the same crater. This cone steamed heavily but did not produce eruptions.


Copyright © Boris Behncke, "Italy's Volcanoes: The Cradle of Volcanology"

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