The 15 March 2007 paroxysm of Stromboli: video-image analysis, and textural and compositional features of the erupted deposit

Abstract

On 15 March 2007, a paroxysmal event occurred within the crater terrace of Stromboli, in the Aeolian Islands (Italy). Infrared and visible video recordings from the monitoring network reveal that there was a succession of highly explosive pulses, lasting about 5 min, from at least four eruptive vents. Initially, brief jets with low apparent temperature were simultaneously erupted from the three main vent regions, becoming hotter and transitioning to bomb-rich fountaining that lasted for 14 s. Field surveys estimate the corresponding fallout deposit to have a mass of ∼1.9×107 kg that, coupled with the video information on eruption duration, provides a mean mass eruption rate of ∼5.4×105 kg/s. Textural and chemical analyses of the erupted tephra reveal unexpected complexity, with grain-size bimodality in the samples associated with the different percentages of ash types (juvenile, lithics, and crystals) that reflects almost simultaneous deposition from multiple and evolving plumes. Juvenile glass chemistry ranges from a gas-rich, low porphyricity end member (typical of other paroxysmal events) to a gas-poor high porphyricity one usually associated with low-intensity Strombolian explosions. Integration of our diverse data sets reveals that (1) the 2007 event was a paroxysmal explosion driven by a magma sharing common features with large-scale paroxysms as well as with “ordinary” Strombolian explosions; (2) initial vent opening by the release of a pressurized gas slug and subsequent rapid magma vesiculation and ejection, which were recorded both by the infrared camera and in the texture of fallout products; and (3) lesser paroxysmal events can be highly dynamic and produce surprisingly complex fallout deposits, which would be difficult to interpret from the geological record alone.