Publication Date:
2013-12-29
Description:
[1] The type of explosive activity known as strombolian is characterized by repeated, low energy, explosions and is named after the volcano where such activity has persisted for around 2000 years, i.e., Stromboli (Aeolian Islands, Italy). Because activity is virtually guaranteed, Stromboli represents an excellent laboratory where measurements of the explosions can be made from safe, but close, distances. During a field campaign in 2008, two 15 cm-diameter bombs, were quenched and collected shortly after a normal explosion. The bombs were characterized in terms of their textural, chemical, rheological and geophysical signatures. The vesicle and crystal size distribution of the samples, coupled with the glass chemistry, enabled us to quantify variations in the degassing history and rheology of the magma resident in the shallow, near-surface, open-vent system (i.e., in last 250 meters of conduit length). The different textural facies observed in these bombs showed that fresh magma was mingled with batches of partially to completely degassed, oxidized, high crystallinity, high viscosity, evolved magma. This magma sat at the top of the conduit and played only a passive role in the explosive process. The fresh, microlite-poor, vesiculated batch, however, shows a response to the explosive event, by undergoing rapid decompression. Integration of geophysical measurements with sample analyses indicates that popular bubble-bursting models may not fit this case. We suggest that the degassed, oxidized magma forms a plug, or rheologically defined layer, at the top of the conduit, through which the fresh magma bursts. In this model we need to consider the paradox of a slug ascending too fast through a magma that is a mixture of magma batches of varying viscosity and yield strength.
Print ISSN:
0148-0227
Topics:
Geosciences
,
Physics
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