Variable Magnitude and Intensity of Strombolian Explosions: Focus on the Eruptive Processes for a First Classification Scheme for Stromboli Volcano (Italy)

Abstract

Strombolian activity varies in magnitude and intensity and may evolve into a threat for the local populations living on volcanoes with persistent or semi-persistent activity. A key example comes from the activity of Stromboli volcano (Italy). The “ordinary” Strombolian activity, consisting in intermittent ejection of bombs and lapilli around the eruptive vents, is sometimes interrupted by high-energy explosive events (locally called major or paroxysmal explosions), which can affect very large areas. Recently, the 3 July 2019 explosive paroxysm at Stromboli volcano caused serious concerns in the local population and media, having killed one tourist while hiking on the volcano. Major explosions, albeit not endangering inhabited areas, often produce a fallout of bombs and lapilli in zones frequented by tourists. Despite this, the classification of Strombolian explosions on the basis of their intensity derives from measurements that are not always replicable (i.e., field surveys). Hence the need for a fast, objective and quantitative classification of explosive activity. Here, we use images of the monitoring camera network, seismicity and ground deformation data, to characterize and distinguish paroxysms, impacting the whole island, from major explosions, that affect the summit of the volcano above 500 m elevation, and from the persistent, mild explosive activity that normally has no impact on the local population. This analysis comprises 12 explosive events occurring at Stromboli after 25 June 2019 and is updated to 6 December 2020.

Unoccupied Aircraft Systems (UASs) Reveal the Morphological Changes at Stromboli Volcano (Italy) before, between, and after the 3 July and 28 August 2019 Paroxysmal Eruptions

“…The differences mentioned above could be the results of structural changes that occurred in the shallower portion of the central conduits after the 2007 eruption [32]. However, analyzing the magmatic and structural processes involved in the 2019 eruptions and leading to further interpretations is beyond the scope of this paper and the reader is referred to the recent literature for additional details [27,34,38,39,68,69].…”

Classifying Major Explosions and Paroxysms at Stromboli Volcano (Italy) from Space

“…To assess the hazards faced by communities living on the island, it is fundamental to detect the explosions of different magnitude and intensity and understand how to classify them. The classification being a paramount issue for a correct hazard assessment [7], in the last decades several classifications have been proposed. Barberi et al [8] distinguished three types of eruptive activity on a growing scale: (1) a persistent, ordinary explosive activity of low intensity, (2) major explosions and (3) paroxysmal events.…”

“…The persistent activity at Stromboli is characterized by several hundreds of short explosive transients (<10 s) per day erupting small ash columns (<100 m) that normally have no impact on the local population [7]. Conversely, the more intense and powerful explosions correspond to greater magnitude (i.e., erupted volume; [9]) and intensity (i.e., instantaneous effusion rate; [10]), resulting in longer explosive transients and higher eruptive columns [7,11].…”

“…Remote Sens. 2021, 13, x FOR PEER REVIEW 2 o paramount issue for a correct hazard assessment [7], in the last decades seve classifications have been proposed. Barberi et al [8] distinguished three types of erupt activity on a growing scale: (1) a persistent, ordinary explosive activity of low intens (2) major explosions and (3) paroxysmal events.…”

“…Phenomena observed during Strombolian paroxysms may vary case by case [7]. instance, large volumes (~10 5 m 3 ) of PDC are often ejected along the Sciara del Fu during paroxysms, whereas they are normally absent during major explosions, and thi Paroxysms are characterized by eruptive columns rising a few km above the craters and causing fires and damage to the populated villages on the lower flanks of the volcano, 2.0-2.5 km away from the summit craters [8,[16][17][18][19].…”