Mount Etna and the 1971 eruption - The collection and analysis of volcanic gases

Abstract
A French team, with workers from Centre d’Etudes Nucleaire, Fontenay, Commissariat a l’Energie Atomique, and Centre National des Recherche Scientifique, have conducted numerous missions to Etna in recent years and these will be briefly reviewed (Tazieff, Boulay, Garrand & Maulard 1968; Boutry & Jatteau 1968; Elskens 1969; Tazieff et al. 1969). Pre-1971 missions In 1969, the central crater had many deep explosions (figure 1). Of particular interest was the Bocca Nuova, a small vent, 6 to 7 m in diameter, which displayed vigorous high temperature gas emission. The gases were emitted in gusts with a regular period, and their physical and chemical characteristics were studied. The maximum water content was of the order of 30 to 40 %. The periodic explosions could be correlated with carbon dioxide contents of 40 to 60 %. All the gas samples taken from the Bocca Nuova were heavily contaminated with air, this could be due to either air percolating through the porous superstructure of the volcano into the vent throat, or by air being sucked into the vent via the orifice in between gusts. The latter is supported by measurements of velocity and a film taken of the phenomenon. In 1970, Le Guern & Le Bronec noted that the central crater was in the same state as 1969. Many explosions were taking place at the bottom of the chasm, which at the surface had dimensions of 200 m by 300 m. The ejectamenta accompanying the explosions rarely reached the top lip due to the great depth. The crater was filled with dense volcanic fumes which occasionally cleared, allowing a glimpse of the vertical walls, and by night, to see the explosive activity at the bottom.

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