Classification, landing distribution, and associated flight parameters for a bomb field emplaced during a single major explosion at Stromboli, Italy

Abstract

International audienceWe propose a novel approach to studying a ballistic bomb deposit. Favorable circumstances, a unique dispersal axis, an operational thermal video camera, and application of an innovative methodology allowed estimates of volume and mass erupted, and definition of mass partitioning between bombs of various sizes. This allowed the creation of a multidisciplinary database for a single major explosion at Stromboli volcano (Italy), the type locality of Strombolian eruptions. The dispersion and direction of the deposit were consistent with a major explosion on 21 January 2010. Field data comprised 780 mapped bomb locations and sizes, and were organized into a GIS with a lidar-derived digital elevation model as its base. This allowed us to define the landing distribution and flight parameters for erupted bombs. The data defined discontinuous deposition to build a cluster-dominated bomb field, with a total deposit volume of ∼10 m3, a mass of ∼2 × 104 kg, and a grain size dominated by large bombs (1 m in diameter). The parameters defined here for a major eruption at Stromboli show that the Strombolian style of volcanism, and its deposits, need to be treated carefully, and a different approach is needed in the future to truly characterize and classify such small (but globally common) explosive eruptions. The recognition that sedimentation from such eruptions will be uneven leads to the important conclusion that isopachs and isopleths cannot be used to estimate eruption volumes for such explosions

The Communication and Risk Management of Volcanic Ballistic Hazards

“…Generally, the distance travelled and the total area impacted by ballistics increases with increasing explosivity, i.e. particles generally travel further and cover a greater area in Vulcanian eruptions (Nairn and Self 1978;Alatorre-Ibargüengoitia et al 2012;Maeno et al 2013) compared with Strombolian eruptions (Harris et al 2012;Gurioli et al 2013;Turtle et al 2016). However, eruptions can be directed, ejecting ballistics at low angles and at distances greater than those from more vertically directed eruptions Tsunematsu et al 2016).…”

“…When isopleths of particle size are included these rarely contain individual measurements and may be severely limited by the availability of only specific mapped locations (e.g., Kilgour et al 2010;Houghton et al 2011). For this reason, the number of particles, sizes of particles, and spatial density per unit area is rarely reported (only four publications could be found with this level of detail- Pistolesi et al 2008;Swanson et al 2012;Gurioli et al 2013;Kaneko et al 2016). This leads to a limited understanding of the hazard and risk posed to the area.…”

“…Blong (1981), Pomonis et al (1999) and Jenkins et al (2014) estimate a ballistic only needs 400-1000 J of kinetic energy to penetrate a metal sheet roof, far less than the estimated kinetic energy of ballistics (*10 6 J) from VEI 2-4 eruptions (Alatorre-Ibargüengoitia et al 2012). The distribution (distance from vent, direction, area and density) of ejected ballistics is controlled by the explosivity, type, size and direction of explosive eruptions, and usually creates spatially variable deposits (Gurioli et al 2013;Breard et al 2014;Fitzgerald et al 2014). Generally, the distance travelled and the total area impacted by ballistics increases with increasing explosivity, i.e.…”

“…The directionality of these blasts is often unpredictable, and can be influenced by external factors such as landslides (Christiansen 1980;Breard et al 2014), making it difficult to deterministically forecast future ballistic distributions. Mapped deposits from past eruptions are often not symmetrical around the vent, reflecting this directionality (Minakami 1942;Fudali and Melson 1972;Steinberg and Lorenz 1983;Kilgour et al 2010;Houghton et al 2011;Gurioli et al 2013;Fitzgerald et al 2014), and are sometimes the result of the crater and surrounding topography Tsunematsu et al 2016). Detailed descriptions and maps of ballistic impact distributions are rare, but those published may contain some of the following data: maximum ballistic travel distances (Steinberg and Lorenz 1983;Robertson et al 1998;Kaneko et al 2016); the outer edges of a ballistic field (Minakami 1942;Nairn and Self 1978;Yamagishi and Feebrey 1994); and/or maximum particle (Nairn and Self 1978;Steinberg and Lorenz 1983;Robertson et al 1998;Swanson et al 2012) or crater size (Robertson et al 1998;Maeno et al 2013;Kaneko et al 2016).…”

“…Ballistic hazard map zones may be classified by maximum travel distance of particles (either any size or a specific sized particle; Alatorre-Ibargüengoitia et al 2012), number of ballistic impacts per unit area (Gurioli et al 2013), probability of a specific size of ballistics reaching a given area (Artunduaga and Jimenez 1997), or probability of a specific consequence occurring e.g. death, injury, damage .…”