Italy's Volcanoes: The Cradle of Volcanology

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The 1985-1995 unrest at Vulcano

20 September 1989
20 September 1989

30 March 1990

30 March 1990

6 November 1990
6 November 1990

18 March 1992
18 March 1992

18 April 1995
18 April 1995

13 September1995
13 September 1995

Comparison photographs taken from the highest point on the SW rim of the Gran Cratere, showing variations of the fumarolic activity between September 1989 and September 1995. Note village of Vulcano Porto in the background.

Since the end of the 1888-1890 eruption, there have been two major episodes of increased fumarolic and seismic activity, one in the mid-1920's and another one starting in 1985 that seems to have delined in 1995. Montalto (1996) speculates that the recent increased activity could have been triggered by a magmatic intrusion to shallow depth. Much of the following is summarized from Montalto (1996); more recent (post 1991) data are from various sources.

The first notable event that affected Vulcano after the 1920s' increased fumarolic activity was a magnitude 5.5 earthquake on 15 April 1978 (causing about 8 deaths in northern Sicily). Its hypocentral area lay about 5 km south of Vulcano. Starting in 1985, there was an increase in the fumarole temperature from about 200 to about 300° C and in the overall gas output from the fumaroles at the Gran Cratere. This was accompanied by changes in the chemical composition of the fumarolic gases. New fractures and vents opened on the N rim of Gran Cratere, and notable ground deformation was observed (Montalto 1996).

Increased shallow seismic activity (a swarm of high-frequency events) began on 25 April 1985 and lasted until 5 June, then was followed by another one from 8 July until 25 August 1985. This was accompanied by an increased steam output from fumaroles at Gran Cratere and other hydrothermal phenomena. Both seismic swarms were accompanied by inflation.

Sulfur deposits
Sulfur deposits on the N rim of the Gran Cratere, September 1995. Much of this area has not been visible due to dense steam clouds in the past years; the diminished fumarolic activity of 1995 makes the fumarolic area more accessible.

From late 1986 to early 1987, fumarole temperatures at Gran Cratere. rose gradually from about 300 to >400° C, and new fumarole fissures and vents became active on the N crater rim and on the N flank of the Fossa cone. A part of the NE flank of Fossa cone collapsed on 20 April 1988, during a period of high regional seismic activity (lasting from March until June 1988). Early speculations that this landslide was triggered by a small phreatic explosion in that area proved incorrect.

A new episode of increased local seismicity began on 9 August 1988, affecting mostly the S part of Vulcano island. This activity levelled off on 14 August but was immediately followed by shallow events immediately below the Gran Cratere, lasting until October 1988. Thereafter, a marked increase in the fluid output of the fumaroles was observed, together with an increase in the soil CO2 output.

The period December 1989-May 1990 was characterized by areal contraction which is interpreted by Montalto (1996) as a possible sign of cooling and crystallization of a shallow magma body emplaced sometime during the increased activity observed before. Another similar event took place before February 1991.

Seismic activity during 1992 was slightly more intense than during 1991, and most of the earthquake epicenters were located around the Gran Cratere. During 1993 there was a marked diminuition of seismic activity on and around the island, and this trend continued through late June 1994. A swarm of 65 earthquakes, the largest of which had a magnitude of 4.0, occurred between 3 and 25 July 1994, arousing some concern among residents and the local authorities. The epicenters lay off the SSW coast of the island. Another slight increase of the seismicity occurred in October-November 1994 (Barberi, Bertagnini and Landi, 1994).

Fumarole temperatures peaked in 1993 when almost 700° C were measured in a fumarole on the inner N wall of the Gran Cratere. After mid-1993, there was a slow diminuition of the measured maximum temperatures, and between 1995 and 1998 they ranged from 400 to 500° C (La Volpe et al., 1999).

Since 1994, also the visible activity has shown a progressive decrease (see the comparison images at right). On 18 April 1995 fumarolic activity at the N rim of Gran Cratere had notably diminished but become more vigorous in the deep central pit of the crater. A further notable decrease of the visible fumarolic activity on Gran Cratere's N rim was evident during a visit on 13 September 1995. There was continuing fumarolic activity in the upper Forgia Vecchia crater where strong hydrothermal alteration is continually undermining the steep and unstable slope immediately above the village of Vulcano Porto. Similar conditions were found during a visit to the crater on 22 September 1996. During a period of humid weather in late April 1997, large steam plumes were again visible over the Gran Cratere, but shortly thereafter, with less relative humidity, the emissions were again very minor.

Another visit to the crater on 26 October 1997 showed that there was no significant change in the visible fumarolic activity since September 1996. The most active fumaroles were on the northern inner slope of the Gran Cratere while the fumaroles on the northern rim were less active than during the period 1989-1995.

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

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