Citation

Montalto A. Nat. Hazards 1995; 11(1): 57-73.

Copyright

(Copyright © 1995, Holtzbrinck Springer Nature Publishing Group)

DOI

10.1007/BF00613310

PMID

unavailable

Abstract

Active volcanic areas are sometimes affected by phreatic eruptions, which are explosions due to the outbreak of a confined pocket of steam and gas without the direct involvement of molten magma. Eruptive activity at 'La Fossa' Volcano, Island of Vulcano (Italy), typically starts with a phreatic explosion, continues as phreatomagmatic and turns into a late magmatic stage, depending on the reduction in the efficiency of magma-water interaction. The present risk is mainly related to a village located at the very foot of the active volcanic cone, which in summer seasons is inhabited by more than 10,000 people. Because the last eruptive episode occurred in 1888-1890, when no local instrumental control was performed, the scientific community does not have any information about the seismic phenomena which could precede the initial phreatic blast. Inferences from similar monitored volcanoes, which awakened in the last few years after more or less long quiescence, are therefore made to tentatively depict possible pre-eruptive seismic scenarios and also to evaluate the most appropriate surveillance and alert criteria to adopt. Appreciable signs of volcanic unrest have been detected in recent years, mainly related to modifications in the physical and chemical features of fumarolic fluids discharged at the active crater. Following the classification of local seismic shocks, the recording oflong-period events (peak frequency ≤2 Hz) should be taken into account as a realistic seismic warning of volcanic hazard enhancement. A likely short-term seismic precursor may be finally given by the appearance of the so-calledbanded tremor, a seismic signal likely produced by intermittent hydrothermal boiling accompanying the hydraulic fracturing of rocks at the top of a pressurized aquifer. Real-time recognition of tremor can be therefore very useful to avoid, at least, injuries to volcanologists and visitors working or staying on the most dangerous sectors of the volcano.

Language: en