Modelling pyroclastic density currents from a subplinian eruption at La Soufrière de Guadeloupe (West Indies, France)

Abstract

We have used a three-dimensional, non-equilibrium multiphase flow numerical model to simulate subplinian eruption scenarios at La Soufrière de Guadeloupe (Lesser Antilles, France). Initial and boundary conditions for computer simulations were set on the basis of independent estimates of eruption source parameters (i.e. mass eruption rate, volatile content, temperature, grain size distribution) from a field reconstruction of the 1530 CE subplinian eruption. This event is here taken as a reference scenario for hazard assessment at La Soufrière de Guadeloupe. A parametric study on eruption source parameters allowed us to quantify their influence on the simulated dynamics and, in particular, the increase of the percentage of column collapse and pyroclastic density current (PDC) intensity, at constant mass eruption rate, with variable vent diameter. Numerical results enabled us to quantify the effects of the proximal morphology on distributing the collapsing mass around the volcano and into deep and long valleys and to estimate the areas invaded by PDCs, their associated temperature and dynamic pressure. Significant impact (temperature > 300 °C and dynamic pressure > 1 kPa) in the inhabited region around the volcano is expected for fully collapsing conditions and mass eruption rates > 2 × 107 kg/s. We thus combine this spatial distribution of temperature and dynamic pressure with an objective consideration of model-related uncertainty to produce preliminary PDC hazard maps for the reference scenario. In such a representation, we identify three areas of varying degree of susceptibility to invasion by PDCs—very likely to be invaded (and highly impacted), susceptible to invasion (and moderately impacted), and unlikely to be invaded (or marginally impacted). The study also raises some key questions about the use of deterministic scenario simulations for hazard assessment, where probability distributions and uncertainties are difficult to estimate. Use of high-performance computing techniques will in part allow us to overcome such difficulties, but the problem remains open in a scientific context where validation of numerical models is still, necessarily, an incomplete and ongoing process. Nevertheless, our findings provide an important contribution to the quantitative assessment of volcanic hazard and risk at La Soufrière de Guadeloupe particularly in the context of the current unrest of the volcano and the need to prepare for a possible future reawakening of the volcano that could culminate in a magmatic explosive eruption.

Magmatic Processes at La Soufrière de Guadeloupe: Insights From Crystal Studies and Diffusion Timescales for Eruption Onset

“…CE eruption is interpreted as a VEI 3 sub-Plinian eruption with a short-lived column reaching, which transported juvenile material, and associated column-collapse and scoriaceous pyroclastic density-currents up to 6 km from the vent (Komorowski, 2008;Komorowski et al, 2012;Komorowski et al, 2013). The combined pyroclastic DRE erupted volume is ∼0.06 km 3 (Boudon et al, 2008;Komorowski, 2008;Legendre, 2012;Esposti Ongaro, 2020). The 1530 Cal CE eruption is used as a calibrated scenario for a future magmatic eruption, as it is representative of La Soufrière Allard et al, 2014;Pichavant et al, 2018).…”

The Basse-Terre Island of Guadeloupe (Eastern Caribbean, France) and Its Volcanic-Hydrothermal Geodiversity: A Case Study of Challenges, Perspectives, and New Paradigms for Resilience and Sustainability on Volcanic Islands

“…Although, several more intense explosive eruptions have been identified at La Soufrière in the last 10,000 years. Even though less intense than magmatic eruptions, the more frequent non-magmatic eruptions of La Soufrière can generate small pyroclastic flows (Esposti Ongaro et al 2020 [113]), lateral directed explosion with blast (Boudon et al 1984 [114]) and, of course, tephra fall (e.g., volcanic bombs, lapilli, and ash). The state of the art of knowledge of phreatic and hydrothermal eruptions shows that they are typically frequent and sudden, that their precursor signals are frequently absent or even few and equivocal, that they are characterized by a very long duration and variable intensity, and that the associated phenomena are very varied and can be particularly dangerous in the proximity (Barberi et al 1992;Christenson et al 2010;and Kato et al 2015 [115-117]).…”

“…A restoration of the pre-shock conditions has too elevated costs to be feasible and implies an almost full reset of the local socio-economic model. On the contrary, eruptions such as the 1976-1977 (VEI ~2) might be fully managed at a local and/or regional scale for its whole duration at a comparably limited cost mainly determined by the disruption of activities in the close surroundings of La Soufrière (~2-3 km of radius; Esposti Ongaro et al 2020 [113]) and, if necessary, temporary evacuations of the resident population. This goes beyond the scopes of this paper, but it is clear that local responsive policies should then be able to include the displacement, by zonal sectors, of some activities and businesses, such as tourism, wellbeing and agri-food activities…”

Energy facies: A global view of pyroclastic currents from vent to deposit

“…The distributions of the deposit thickness, lithic and juvenile clasts and temperature in pyroclastic successions are key, as they record the macroscopic eruptive conditions that occur in ancient explosive volcanic eruptions. They also give insights on the temporal evolution of pyroclastic currents at active volcanoes, where the source dynamics can be better constrained and the topographic interaction can be inferred Cas et al, 2011;Cashman & Giordano, 2014;Di Vito et al, 2009;Doronzo, 2012;Doronzo et al, 2017;Dufek & Bergantz, 2007;Esposti Ongaro et al, 2020;Giordano & Doronzo, 2017;Guzman et al, 2020;Palladino et al, 2014;Palladino & Giordano, 2019;Wright et al, 2016).…”

“…It is similar to Energy facies 5 but represents its evolution as a topography-surviving current (Table 2). Energy facies 5, 6 and 7 have been recognized for Mount St. Helens, Colli Albani PNO, Vulcano and Soufrière de Guadeloupe (Esposti Ongaro et al, 2012;Esposti Ongaro et al, 2020;Giordano & Doronzo, 2017;Doronzo et al, 2017; see Table 1).…”