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Large volcanic explosions are well known to be capable of exciting a range of atmospheric waves including sound, infrasound, and acoustic-gravity waves (AGW), that can be recorded at very large distances from the source. Understanding their generation and propagation is important to correctly interpret recorded signals and retrieve source parameters, as well as to study atmospheric phenomena of the upper layers of the atmosphere, such as the formation of ionospheric traveling disturbances associated with propagating Lamb waves. Most studies rely on models based on a simplified (linearized) version of the Navier-Stokes equations that do not allow to fully investigate the effects due to the complexity of volcanic sources (presence of gas particle mixtures, shock waves, directivity of the volcanic jet) and to non-linear propagation phenomena. Here, we present preliminary results and efforts to test, within the open-source MagmaFOAM framework, based on the OpenFOAM library, a numerical model that solves the full set of equations for compressible fluids, including the presence of multiple phases (e.g. gas-particles) and components (e.g. air-water vapor). The model is able to consider the relatively large atmospheric computational domains that are required to study AGW. The validated model may provide the opportunity to investigate the generated wavefield for selected eruption source processes and scenarios as well as to test simplified source models., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

Nucleation and growth of crystals, and the resulting crystal size distribution, play a fundamental role in controlling the physical properties of magmas and consequently the dynamics of the eruptions. In the past decades, laboratory experiments demonstrated that size and shape of crystals strongly control the physical properties of magma and lava. Additionally, natural and experimental samples are usually characterized in terms of their crystal size distribution to link it with physical processes that are not directly observable, such as cooling or decompression mechanisms. In this paper, we present CrystalMoM, a new predictive model, based on the quadrature-based method of moments, developed for studying the kinetic of crystallization in volcanic systems. The quadrature-based method of moments, well established in the field of chemical engineering, represents a mesoscale modelling approach that rigorously simulates the space–time evolution of a distribution of particles, by considering its moments. The method is applied here, for the first time, for studying the equilibrium/disequilibrium crystallization in magma, modelling the temporal evolution of the moments of a crystal size distribution. The model, verified against numerical and experimental data, represents a valuable tool to infer the cooling and decompression rates from the crystal size distribution observed in natural samples.

Nucleation of water gas bubbles in trachyphonolitic magmatic melts has been investigated integrating theory and numerical modelling with decompression experiments and analysis of natural ash samples of explosive eruptions. Bubble nucleation, considered the natural response of magmas to decompression, is strongly dictated by the gas-melt surface tension. Here, I use an integrated approach to quantify the role of the surface tension in the nucleation process combining high pressure - high temperature nucleation experiments with a numerical modelling based on the gradient theory (Cahn and Hilliard, 1959). This theory, successfully applied in several studies of industrial polymers (Poser and Sanchez, 1981; Harrison et al., 1999; Kahl and Enders, 2000; Enders et al., 2005) was never been used before to study systems of volcanological interest. I show that surface tension is far to be a constant, but it decreases with in- creasing nucleation pressure (i.e. the confining pressure). Entering the values of surface tension into the classical theory of nucleation, I obtain a variable supersaturation pressure triggering nucleation. The decreasing value of the gas-melt surface tension with increasing pressure, facilitate bubble nucleation at high pressure, thus enhancing the explosivity of eruptive events from deeper reservoirs. Instead, the hindered nucleation at relatively low pressure, due to high bubble surface tension, implies that the generation of explosive eruptions from shallow reservoirs requires high decompressions. Finally the vesiculation, in terms of nucleation and growth, of natural samples of ash-rich eruptions has been studied by applying a novel technique able to take 3D measurements of bubbles preserved on ash particle’s surface. The Bubble Size Distributions (BSD), together with the field evidence, suggest that the ash production in these ash-rich eruptions, rather than to magma-water explosive interaction, is related to the high decompression necessary to nucleate bubbles in a shallow reservoir.