Ash erupted during normal activity at Stromboli (Aeolian Islands,Italy) raises questions on how the feeding system works |
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Authors: | Email author" target="_blank">Claudia?D’OrianoEmail author Antonella?Bertagnini Massimo?Pompilio |
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Institution: | (1) Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Pisa, Via della Faggiola 32, 56126 Pisa, Italy |
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Abstract: | Ash fallout collected during 4 days of sampling at Stromboli confirms that a crystal-rich (HP) degassed magma erupts during
the Strombolian explosions that are characteristic of the normal activity of this volcano. We identified 3 different types
of juvenile ash fragments (fluidal, spongy and dense), which formed through different mechanisms of fragmentation of the low-viscosity,
physically heterogeneous (in terms of the size and spatial distribution of bubbles) shoshonitic magma. A small amount (less
than 3 vol%) of volatile-rich magma with low porphyricity (LP), erupted as highly vesicular ash fragments, has been collected,
together with the HP magma, during normal strombolian explosions. Laboratory experiments and the morphological, textural and
compositional investigations of ash fragments reveal that the LP ash is fresh and not recycled from the last paroxysm (15
March 2007). We suggest that small droplets of LP magma are dragged to the surface by the time-variable but persistent supply
of deep derived CO2-rich gas bubbles. This coupled ascent of bubbles and LP melts is transient and does not perturb the dynamics of the HP magma
within the shallow reservoir. This finding provides a new perspective on how the Stromboli volcano works and has important
implications for monitoring strategies. |
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