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 - 1992-1993

Lava fountain erupting from a shield-like vent in the center of Crater 1 in early May 1993, during a phase of dramatically increased activity. This photo was taken by Stephen O'Meara of Sky And Telescope. The large version of this image is available at Volcano World, click on the image to get connected.

I did not see the summit of Stromboli in 1992 and 1993. This photo of Jon Dehn shows the crater and the N slope of Sciara del Fuoco abount one month after the brief effusive episodes of mid-May 1993. The new flow lobes show clearly on the slope below Crater 1, reaching a length of max 150 m. Nine months later, during my first summit visit since August 1991, the flows were completely buried under material ejected by the violent October 1993 explosions. Note the filling of Crater 1 with small cones.

Early morning explosion from central vent in Crater 1, June 1993. The large version of this photo shows large glowing bombs within and beyond the ash column. Ash eruptions from Crater 1 are much less common than those from Crater 3. This notable photograph was taken by Jon Dehn.

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

Stromboli had three major eruptive events in 1993, departing from its usual persistent small-scale activity. The first one of these was a powerful explosion on 10 February that caused tephra falls in Ginostra village. The second significant event was a period of unusually intense activity in April-May 1993 that culminated in two brief episodes of lava flow emission; the third, early on 16 October 1993, was a powerful explosion that deposited large bombs on Pizzo sopra la Fossa. The latter event, had it occurred during the high season, with tens of tourists camping on the summit, could have had serious consequences.

The 10 February explosion was accompanied by a "lateral blast" and generated small pyroclastic avalanches on the Sciara del Fuoco (Bonaccorso et al., 1996), and it appears that the activity had both magmatic and phreatomagmatic components. For some time after this explosion the activity was at low levels, but then increased again.

When visited in early May 1993, Stromboli was more vigorously active than it had been for many years. The activity was practically continuous and small scoria cones grew rapidly in Crater 1. Small lava flows within Crater 1 were witnessed during the night of 2-3 May 1993, but larger flows flowed out of that crater onto the N part of Sciara del Fuoco on 15 and 18 May 1993. These lava flows, the first since the 1985-1986 eruption, moved only about 300 m down the northern part of the Sciara del Fuoco.

Activity continued at a "normal" scale through mid-October 1993. On the early morning of 16 October 1993, residents of the island were awakened by powerful detonations. One person who was sleeping immediately below the Pizzo sopra la Fossa, in what seemed to be a relatively safe place, had a narrow escape from falling bombs; her sleeping bag was burned by a large bomb. This woman and another person who was on the Pizzo sopra la Fossa at the time of the explosion, received burns and traumas from falling incandescent pyroclastics, none of these, fortunately, of the size of those that burned the sleeping bag. At daybreak, a light ash deposit was discovered to have covered Stromboli village. Investigation of the summit area by Jürg Alean (Stromboli On-line) and his wife the day after revealed that large fluid ("cowdung") bombs had fallen onto the outlook platform of Pizzo sopra la Fossa, some having diameters of >30 cm. Impressive photos are available at Stromboli On-line.

It appears that the explosion originated at Craters 1 and 2, and all material - pyroclastics and the intracrater cones formed in May - was blown out of these craters. Strong explosive activity continued for about 10 minutes, and this event was described as the largest explosive event at Stromboli in 10 years (Bonaccorso et al., 1996). For several weeks after the explosion the activity was at low levels, but returned to normal late in the year.

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

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