Ash erupted during normal activity at Stromboli (Aeolian Islands, Italy) raises questions on how the feeding system works
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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.
KeywordsStromboli Strombolian activity Ash Paroxysms Clast morphology Glass chemistry Bubble ascent
We are indebted to A. Aiuppa for constructive criticisms and to B.F. Houghton for the stimulating review and his noble forgiving character. We thanks M. Marsella for providing digital elevation model of Stromboli and A. Cavallo for technical assistance in EMP analyses. C.D. was funded by MIUR project: Advancing Interdisciplinary Research Platform on Volcanoes and Earthquakes (AIRPLANE). This work was supported by the Project V2-Paroxysm 2007–2009 INGV-DPC agreement.
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