Complex geometry of volcanic vents and asymmetric particle ejection: experimental insights

Abstract

Explosive volcanic eruptions eject a gas-particle mixture into the atmosphere. The characteristics of this mixture in the near-vent region are a direct consequence of the underlying initial conditions at fragmentation and the geometry of the shallow plumbing system. Yet, it is not possible to observe directly the sub-surface parameters that drive such eruptions. Here, we use scaled shock-tube experiments mimicking volcanic explosions in order to elucidate the effects of a number of initial conditions. As volcanic vents can be expected to possess an irregular geometry, we utilise three vent designs, two “complex” vents and a vent with a “real” volcanic geometry. The defining geometry elements of the “complex” vents are a bilateral symmetry with a slanted top plane. The “real” geometry is based on a photogrammetric 3D model of an active volcanic vent with a steep and a diverging vent side. Particle size and density as well as experimental pressure are varied. Our results reveal a strong influence of the vent geometry, on both the direction and the magnitude of particle spreading and the velocity of particles. The overpressure at the vent herby controls the direction of the asymmetry of the gas-particle jet. These findings have implications for the distribution of volcanic ejecta and resulting areas at risk.

Drone deployed sensors: a tool for multiparametric near-vent measurements of volcanic explosions

“…This specific type of activity was especially interesting, since it closely resembles the dynamics of shock-tube experiments [e.g. Cigala et al 2017;Schmid et al 2022].…”

“…With the aid of scaled laboratory experiments as well as numerical and theoretical models, the influence of reservoir volume, pressure and vent geometry have been established [e.g. Ogden et al 2008;Koyaguchi et al 2010;Schmid et al 2020;Cigala et al 2021;Schmid et al 2022]. Thus, a basis for the interpretation of surface signals has been generated and reliable measurements at the vent have become the remaining prerequisite for an estimation of source parameters.…”

UAS‐Based Observations of Infrasound Directionality at Stromboli Volcano, Italy

“…Infrasound can be used to detect, locate, and quantify sources from local to remote distances (De Angelis et al., 2019; Fee & Matoza, 2013; Johnson & Ripepe, 2011; Matoza et al., 2019) and is therefore useful for volcano monitoring. While many explosions may be well‐described by a simple volumetric source (monopole), sources such as buried chemical explosions (e.g., Blom et al., 2020; Kim et al., 2022), complex volcanic eruptions (e.g., Iezzi et al., 2019; Johnson et al., 2008; Jolly et al., 2016, 2017, 2022; Kim et al., 2012; Matoza et al., 2013; Schmid et al., 2020, 2022; Watson et al., 2021), and mass movements (e.g., Johnson et al., 2021; Marchetti et al., 2019; Ripepe et al., 2010; Toney et al., 2021; Ulivieri et al., 2011) can have a significant directional component. Hazardous ballistic and gas trajectories may be consistent with acoustic directionality (Fitzgerald et al., 2020; Jolly et al., 2017).…”

The Effect of Conduit Walls Roughness on Volcanic Jets and Their Seismo‐Acoustic Radiation: An Experimental Investigation

“…High values of conduit length to diameter ratio, as in volcanic explosion occurring at depth, increase the thickness of the initial shear layer: for fixed diameters, the higher the length of the pipe the higher the initial thickness of the shear layer (e.g., Jothi & Srinivasan, 2009). Similarly, the geometrical properties of jet nozzle have been shown to modulate jet structures: amongst others the arrangement of chevrons at the nozzle (e.g., Bridges & Brown, 2004; Heeb et al., 2016), the geometry of the exit vent (e.g., Cigala et al., 2017; Schmid et al., 2022; Swanson et al., 2018), pipe surface roughness at the micron scale (e.g., Jothi & Srinivasan, 2013). Clearly, it is of paramount importance to map the effect of complex volcanic geometries on observable parameters through well‐constrained aeroacoustics laboratory studies.…”