Dynamics and tephra dispersal of Violent Strombolian eruptions at Vesuvius: insights from field data, wind reconstruction and numerical simulation of the 1906 event

Abstract

Mt. Vesuvius is one of the most studied volcanoes in the world and its proximity to an extremely populated area makes it also one of the most threatening. Violent Strombolian (VS) events have occurred in the most recent history of the volcano, and they are the type most likely to occur in case of reactivation of the volcano in the near future. In order to investigate the dynamics and hazard of this type of eruption, we performed new field and laboratory work and numerical simulations of plume dynamics, fallout and tephra dispersal associated with such eruptions. Attention was specifically focused on the 1906 eruption, a recent and well-studied VS event. Based on new field analyses and historical observations, we reconstructed the temporal evolution of eruption source conditions during the event. The reconstructed explosive phase of the eruption is inferred to have been 8 days long and characterized by two distinct stages: a former short and intense period with sustained convective plume fed by powerful lava fountains (20 h) followed by a prolonged and less intense period of ash emission (172 h). The total grain-size distributions for both phases, used as inputs to the model, were obtained by field work and laboratory analyses. Based on these new volcanological data and reconstruction of wind field direction and intensity, partially derived from historical sources, the 1906 event was numerically simulated and results compared to deposit distributions. The modelling outcomes for the ash emission phase provide a better agreement with the measured tephra mass load for a simulation run in which ash aggregation (described by the models of Cornell et al. J Volcanol Geotherm Res 17:89-109, 1983, and Biass et al. Nat Hazard Earth Syst Sci 14:2265-2287, 2014) is specifically taken into account, confirming the importance of this process during tephra dispersal. The aggregation model that best fits the simulated results to the measured ground loadings has 80 % of particles Φ≥4 that aggregate uniformly in the range Φ=−1 to 3. Two additional simulations of a VS event were carried out by using meteorological data of two specific periods to exemplify weather's potential on impacts of such eruptions, particularly tephra loading, on the surrounding areas. The model outcomes clearly highlight the major effects of differences in local meteorology on plume dynamics and ash dispersal and the key role of wind shear in determining the cumulative thickness of ground deposits. Results also show that, due to the long duration of this kind of eruption and the large variability in zonal winds at this latitude, ash dispersal and fallout from VS events at Vesuvius represent a probable hazard for all of the territory near Vesuvius, including the city of Naples, where cumulative tephra loadings might reach critical thresholds for roof collapse and infrastructure damage.

Effects of eruption source parameter variation and meteorological dataset on tephra fallout hazard assessment: example from Vesuvius (Italy)

“…Barberi et al 1990;Barsotti et al 2015;Bonadonna et al 2002;Bonasia et al 2011;Capra et al 2008;Costa et al 2009;Hill et al 1998;Jenkins et al 2015;Macedonio et al 2008;Scaini et al 2012;Scollo et al 2008;Sieron et al 2014). However, the eruption source parameters of the considered reference scenario are commonly kept fixed an their variability and uncertainty are rarely taken into account.…”

Assessing future vent opening locations at the Somma‐Vesuvio volcanic complex: 1. A new information geodatabase with uncertainty characterizations

“…Continuous ash emission (AE) eruptions (e.g., AP3, AP4, and AP5, several events of Middle Age activity, 1794, and 1660)-with magnitudes up to 10 −2 km 3 and intensities <10 5 kg/s-resulted in the deposition of sequences (from few centimeters up to several decimeters thick) of ash deposits interlayered with minor lapilli beds. The most important feature of this latter type of activity is its prolonged duration (from weeks to months) (details in Cioni et al [2008] and Barsotti et al [2015]). Cioni et al [2008] discussed in detail the temporal evolution of volcanic activity at SV, by estimating the main physical parameters related to a large set of past eruptions (see Figure 3 from this paper and Table 1 from Cioni et al [2008]).…”

“…Continuous ash emission (AE) eruptions (e.g., AP3, AP4, and AP5, several events of Middle Age activity, 1794, and 1660)—with magnitudes up to 10 −2 km 3 and intensities <10 5 kg/s—resulted in the deposition of sequences (from few centimeters up to several decimeters thick) of ash deposits interlayered with minor lapilli beds. The most important feature of this latter type of activity is its prolonged duration (from weeks to months) (details in Cioni et al [] and Barsotti et al []).…”

“…The small‐scale explosive eruption data set (Figure ) comprises the violent Strombolian (VS) and continuous ash emission (AE) categories, which have been placed here into one data set to reflect similar magnitudes and intensities, although deposits and related hazards are quite different [ Cioni et al , ; Neri et al , ; Barsotti et al , ].…”

Reconstructing eruptive source parameters from tephra deposit: a numerical study of medium-sized explosive eruptions at Etna volcano

“…Tracking puff movements within the 3D domain, the code computes at each time step the amount of mass advected out of the domain, still suspended in the atmosphere and deposited on the ground. VOL-CALPUFF has been tested and adopted to simulate volcanic ash dispersal and deposition at several volcanoes worldwide Barsotti et al 2011;Spinetti et al 2013;Barsotti et al 2015).…”