Italy's Volcanoes: The Cradle of Volcanology

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Volcanic hazards at Vulcano

Although eruptive activity at Vulcano has rarely had major effects beyond the immediate vicinity of the eruption vents, a very high volcanic hazard exists on the island, due to the presence of a settlement and major tourist resorts in an area very likely to be affected by future eruptions. As shown in the section on the geological evolution, Vulcano is capable of displaying eruptive phenomena that are extremely dangerous, if not lethal, to humans

It is very probable that Vulcano will erupt in the future much the same way as it did in the past. Like in the past, the initial activity will probably be strongly influenced by external water as magma will inevitably encounter groundwater levels when rising up to the surface. The initial activity will therefore consist of violent hydrothermal explosions with generation of wet and dry surges and possibly explosion breccias. It will occur either from the present Fossa crater or from a new vent, most probably near the Fossa cone. Since vents have generally shifted westwards or northwards during the eruptive history of Fossa volcano, it is well possible that a new eruption will open a new vent W or N of the present Fossa crater.

Surges produced by the ongoing activity may affect all of the Fossa caldera area if the eruptive vent is assumed to coincide with the present Fossa crater. The thickest deposits from surges will form at the base of the Fossa cone where the abrupt break in the slope will slow their movement. If a new vent opens on the N side of the Fossa crater, the surges will have their maximum destructive force in the area of Volcano Porto village. Effects from surges are known well from recent eruptions such as the 1965 eruption of Taal volcano, Philippines which killed about 190 people. Virtually no one staying in the Fossa caldera (this implies, in the major portion of Vulcano Porto village) would survive the passage of the surges from Fossa crater.

The southern part of Vulcano is considered relatively safe from the surges but falls of bombs like those during the 1888-1890 eruptions could present a hazard to people and their property in that area. The outflow of lava is not considered a dangerous phenomenon.

The volcanic hazard situation on Vulcano is dramatically illustrated in this photo (of March 1992) taken from the steaming crater rim and looking down on the houses of the village and the harbor of Porto Levante (right). The conspicuous rocky feature visible in the right part of the photo is the "Faraglione", an eroded remainder of a small volcanic cone.

A significant hazard exists also when the volcano is not erupting. Part of the N rim of the Gran Cratere is highly unstable due to erosional undercutting and weakening of the rock by hydrothermal (fumarolic) activity persisting since the most recent eruption. The area of greatest instability is above the parasitic Forgia Vecchia craters on the N flank of Fossa cone.

Numerous cracks have already formed in that area indicating that blocks are detaching from the N rim of Gran Cratere and may fall towards Vulcano Porto village at any time. Some of the detached blocks were seen to have subsided by up to 20 cm in September 1995.

A major collapse of the N crater rim will probably unleash a debris avalanche capable of reaching, and covering parts of, Vulcano Porto village. Compared with other volcanic debris avalanches, this one will be extremely small, but since it would fall directly into a population center, it could have devastating consequences.

It is possible that a major collapse of the N crater rim will also have hazardous effects by the uncapping of the hydrothermal system lying immediately below. Steam blasts could be one of those effects which would threaten the village below Fossa cone with the fall of large blocks.

No detailed investigation in the light of eruptive processes and volcanic hazards has until now been made at Vulcanello. A large portion of its cones consists of thinly bedded, fine-grained light-colored tuffs that were probably ejected during phreatic and/or phreatomagmatic activity. Although it apparently has erupted less frequently and its magma production rate in the past 2500 years or so has been siginificantly lower than that of Fossa (1.5 x 104 m3/year compared to 5 x 104 m3/year; Sheridan et al. 1987), it is potentially active and should be considered hazardous. Renewed activity at Vulcanello could encompass hydromagmatic eruptions, Strombolian activity and emission of major lava flows with a higher fluidity than those of Fossa cone. In the case of new eruptive activity at Vulcanello, all buildings (many luxurious villas with beautiful gardens, large hotel complexes, holiday villages and other tourist facilities) are likely to be damaged or destroyed.

Another problem may have arisen since 1995 from the simple fact that Vulcano is quieter since then than during the preceding ten years. As in the case of Vesuvio (Vesuvius), the decline of increased fumarolic output is by many interpreted as a sign that the volcano will not erupt, and this will probably lead to further construction and touristic development in the area of highest risk.


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

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