Catalog of major explosions and paroxysms at Stromboli volcano (Italy) from 1970 to 2023

Abstract

The catalog consists of the dataset of the major explosions and paroxysms recorded at Stromboli from Jan. 1970 to Oct. 2023, as reconstructed through a detailed review of monitoring bulletins and reports, previous catalogs, and scientific literature of the last ca. 50 years. The catalog includes the calendar date, GMT time and phenomena descriptions for 89 explosive events, of which 4 were paroxysms, 51 were major explosions, and 34 were uncertain major explosions, i.e. explosions of unclear characterization that could have been major explosions or ordinary activity.

We detailed the event information content in five columns – (i) seismicity, (ii) sound/air shock, (iii) vents involved, (iv) ash plume/fallout, (v) ballistic projectiles. In addition, we indicated if there were any: (vi) field survey, (vii) pumices erupted, (viii) fires, (ix) map of the products, (x) photo/video of the event, (xi) hot avalanche, (xii) lava flow. The catalog also includes a list of the original literature sources that helped us in the complex characterization of the explosive events. We finally reported if there were people affected by the events, and any previous catalog that comprised them.

In our analysis (see also Bevilacqua et al., 2020b), we mostly relied on the detailed characterization of major explosions and paroxysms in Rosi et al. 2013 that provided quantitative constraints on total duration, fallout volume, mass discharge rate, ballistic size, ballistic range and column height of ordinary activity, major explosions, and paroxysms. In several cases, we had to carefully evaluate the original description of the phenomena, due to insufficient quantitative information in the scientific literature.

In particular, we considered the hazardous area affected by large ballistic projectiles as the main discriminant factor to distinguish between ordinary activity, major explosions and paroxysms. This area is limited to the Crater Terrace and upper Sciara del Fuoco in case of ordinary activity, to the summit area of the volcano and Sciara del Fuoco during major explosions, and can extend down to low elevations along large part of the island, and sometimes beyond the shoreline, during the paroxysms (Barberi et al., 1993). We also considered several other factors, including the height of the plume, the amount of ash and scoria fallout, the occurrence and strength of any associated shock wave. The occurrence of fires associated with the violent explosive activity was assumed as a good marker for a major explosion too (Rosi et al., 2013).

Whilst identifying the paroxysms was relatively straightforward, several possible major explosions were not clearly distinguishable from particularly violent episodes of ordinary Strombolian activity. Thus, our historical record includes the quantification of the main sources of uncertainty, i.e. the possibility of 34 major explosions of uncertain characterization because of insufficient information. We followed a conservative approach and we classified as “uncertain major explosions” all the explosive events for which we could not exclude they were major explosions. This particular case often occurs in the 1970s, 1980s and 1990s, before the installation of surveillance cameras, and, afterwards, when these cameras were not operating for bad weather conditions or temporary malfunctions.

In addition, the catalog includes 41 seismic sequences typically associated with higher-than-usual explosive activity but with a size significantly smaller than that of major explosions. These events may have produced a limited ballistic fallout just outside of the crater terrace, i.e. few tens of meters, or short lived effusive activity (e.g. intra-crateric), but they are not associated with the dangerous ballistic fallout of major explosions.

About these seismic sequences, we relied on the characterization in Falsaperla & Spampinato, 2003, that is a variable number of explosion quakes in rapid succession (i.e. from tens of seconds to a few minutes), associated with a notable increment in the amplitude of volcanic tremor. This definition relies on the availability of seismic registrations, and therefore a significant under-recording may affect the period before June, 1985, when seismic records started to be acquired continuously at Stromboli. Afterwards, short lapses in the available registrations possibly generated slight underrecording of the seismic sequences in the 1990s and 2000s. Since 2003/2004 the improvement in the seismic network significantly reduced the possible underrecording of seismic sequences.

The catalog is accompanied by four supporting files. Supporting Material S1 is a table summary of all the events in the catalog, including a synoptic panel comparing the new catalog to the pre-existing catalogs. Supporting Material S2 is the collection of excerpts from the source documents, including the original figures and descriptions. Supporting Material S3 is the bibliography; a digital version of the literature sources referenced is available from the corresponding author. Supporting Material S4 is an addendum catalog that comprises the descriptions of a number of supplementary explosive events reported as anomalous in literature or monitoring files for various reasons, but not classified by us as paroxysms, major explosions, uncertain major explosions, or seismic sequences.

This catalog is complementary to the historical catalog Bevilacqua et al. (2020a), which comprises the years from 1879 to 1960. In the time interval between 1960 and 1970 no major explosions or paroxysms were recorded; however, some under-recording of major explosions might affect that decade. The modeling and estimation of inter-event time and temporal rate of major explosions and paroxysms at Stromboli volcano is detailed in Bevilacqua et al. (2020b) based on the data available at that time.

Finally, it is worth mentioning that the present catalog is based on the above reported criteria to characterize the ordinary activity, major explosions and paroxysms which are mostly oriented to the assessment of the hazard associated with the explosive activity of Stromboli. It should also be recognized that a well-defined boundary between these categories may not exist. The catalog is open and dynamic and welcomes contributions from other sources and new information in order to make it more complete and robust.