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L’activité volcanique
 du Stromboli : un laboratoire naturel de choix à la base de la classification des projections

Abstract : Textural and chemical analyses of bombs quenched directly from a strombolian explosion were integrated with coincident seismic, acoustic and thermal data, for Stromboli volcano. The data set defines a new gas-dominated type of “strombolian” eruption (Type 0). Type 0 events are characterized by high velocity emission (150-250 m s-1) of a few, relatively small, juvenile particles, with entrained lithics that have fallen back into the vent to be re-erupted. For the studied event, the explosion depth was more than 250 m deep, and the particles showed little residence (degassing) time in the shallow system between the surface and the free magma surface. Slug ascent velocities over the final 20-35 m of magma-filled conduit, and the low viscosity of the resident magma, are all consistent with simple bubble burst in a “clean” conduit. This conduit type and eruption style likely fits popular slug ascent and burst models used to explain “strombolian” eruptions. Our comparison with a Type 1 (ballistic-dominated) eruption shows that such events are associated with larger proportions of degassed material in the shallow system magma mix. We argue that the additional volume of this degassed material pushes the free surface upwards. Because of the larger volume of material available for entrainment into a Type 1 slug burst, which has to fragment through a thick cap of degassed material, Type 1 events tend to be rich in particles. In contrast, the less spectacular, gas-rich (Type 0) events have little material to entrain, thus being poor in lapilli and bombs. Our results also show the importance of sampling the bombs, as well as scoria and ash, during Strombolian events, in parallel with key geophysical and remote sensing measurements. Such a truly multidisciplinary sampling strategy, integrated by textural and geochemical studies, is essential if we are to properly understand, model, and explain the dynamics and mechanisms of Strombolian eruptions, as well as to correctly apply models and assumptions to extract shallow system dynamics from geophysical data sets.
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Estelle Rose-Koga, Lucia Gurioli, Andrew J.L. Harris, Ludovic Leduc. L’activité volcanique
 du Stromboli : un laboratoire naturel de choix à la base de la classification des projections. Revue d'Auvergne, Association des amis des universités de Clermont-Ferrand, 2014, 127, pp.622. ⟨hal-02109221⟩

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