Effects of particle mixtures and nozzle geometry on entrainment into volcanic jets

Jessop, David; Jellinek, M.

doi:10.1002/2014gl060059

Cited by 30 publications

(28 citation statements)

References 22 publications

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“…Valentine (1997) suggested that narrow vents and high exit velocities favour the generation of buoyant plumes. Jessop and Jellinek (2014) investigated the effect of vent geometry on entrainment characteristics of volcanic jets. They found that air entrainment is more efficient for diverging vents because of a larger surface of the jet's boundary layer due to particle inertia and trajectory.…”

Section: Introductionmentioning

confidence: 99%

Release characteristics of overpressurised gas from complex vents: implications for volcanic hazards

et al. 2020

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Many explosive volcanic eruptions produce underexpanded starting gas-particle jets. The dynamics of the accompanying pyroclast ejection can be affected by several parameters, including magma texture, gas overpressure, erupted volume and geometry. With respect to the latter, volcanic craters and vents are often highly asymmetrical. Here, we experimentally evaluate the effect of vent asymmetry on gas expansion behaviour and gas jet dynamics directly above the vent. The vent geometries chosen for this study are based on field observations. The novel element of the vent geometry investigated herein is an inclined exit plane (5, 15, 30° slant angle) in combination with cylindrical and diverging inner geometries. In a vertical setup, these modifications yield both laterally variable spreading angles as well as a diversion of the jets, where inner geometry (cylindrical/diverging) controls the direction of the inclination. Both the spreading angle and the inclination of the jet are highly sensitive to reservoir (conduit) pressure and slant angle. Increasing starting reservoir pressure and slant angle yield (1) a maximum spreading angle (up to 62°) and (2) a maximum jet inclination for cylindrical vents (up to 13°). Our experiments thus constrain geometric contributions to the mechanisms controlling eruption jet dynamics with implications for the generation of asymmetrical distributions of proximal hazards around volcanic vents.

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Section: Introductionmentioning

confidence: 99%

Release characteristics of overpressurised gas from complex vents: implications for volcanic hazards

et al. 2020

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“…The critical condition separating the RSF and non‐RSF regimes and that for column collapse can be affected by other factors. The particle decoupling from gas phase can alter the entrainment properties of plumes (e.g., Cerminara, Esposti Ongaro, & Neri, ; Jessop & Jellinek, ; Jessop et al, ). The crater geometry, such as the opening angle of crater, controls the decompression‐compression processes and the exit velocity at the crater top (Carcano et al, ; Cigala et al, ; Kieffer, ; Koyaguchi & Suzuki, ; Ogden et al, ; Woods & Bower, ) and the entrainment properties (e.g., Cerminara, Esposti Ongaro, & Neri, ; Jessop & Jellinek, ).…”

Section: Discussionmentioning

confidence: 99%

Control of Vent Geometry on the Fluid Dynamics of Volcanic Plumes: Insights From Numerical Simulations

Suzuki

Costa

Koyaguchi

2020

Geophysical Research Letters

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We present three-dimensional numerical simulations of eruption clouds from circular to linear fissure vents to investigate the control of vent shape on the height and stability of volcanic plumes during large explosive eruptions. Our results show that clouds ejected from circular or low-aspect-ratio (nearly square-like) fissure vents can be associated with radially suspended flow (RSF) at the top of the jet region, whereas those emitted from narrow-fissure vents are not. Non-RSF plumes are more stable than those associated with RSF because the highly concentrated parts of the ejected mixture are easily dissipated and mixed with air near the vent. Plume height in the RSF regime decreases while that in the non-RSF regime increases with increasing aspect ratio, even for a fixed magma flow rate. These observations suggest that the efficiency of air entrainment is influenced by the vent shape, which in turn controls the dynamics of eruption plumes.Plain Language Summary Explosive volcanic eruptions eject hot mixtures of gas and ash, forming eruption clouds. Eruption clouds can either become buoyant and rise upward as kilometer-scale volcanic plumes, from which they release ash and gas into the atmosphere, or flow downward along the ground, resulting in devastating pyroclastic flows. Understanding the dynamics of eruption clouds and the critical conditions for generating pyroclastic flows versus volcanic plumes is an important focus of modern volcanology research. We present numerical simulations of eruption clouds using a three-dimensional numerical model to investigate the effects of volcanic vent geometry on plume stability and height. Our simulation results indicate that plume height depends on the shape of the volcanic vent and can have different dynamics even for the same eruption intensity. These effects of vent shape are caused by the complex mechanism of mixing between the eruption cloud and the ambient air. The efficiency of such mixing inside the cloud largely controls the critical conditions for the generation of pyroclastic flows; above a critical mass flow rate, clouds ejected from circular vents can generate pyroclastic flows, whereas those ejected from thin fissure vents develop stable volcanic plumes.

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“…Particles were found to augment the angular momentum of entraining eddies, forcing them to overshoot more deeply into, deform and engulf the ambient fluid. Entrainment in the flow was also enhanced for flared nozzles but it was reduced for cylindrical nozzles (Jessop and Jellinek 2014). Experiments made with linear and annular vents revealed that entrainment was reduced as the vent width became small compared to its length because the size of the entraining eddies scaled with the vent width ).…”

Section: Sustained Plinian Columnsmentioning

confidence: 97%

“…(3) Many aspects of the physics of gas-particle flows, which are ubiquitous in explosive volcanic eruptions at various solid concentrations, remain poorly understood. These include (i) the coupling between the fluid and solid phases and its consequences for the particle concentration and structure of the mixtures (e.g., Breard et al 2016, Weit et al 2019, and (ii) the interaction between these flows and their surrounding environment such as a solid substrate, a water body or the atmosphere (e.g., Jessop and Jellinek 2014). (4) Experimental work related to monitoring studies is likely to increase in the near future as it will help to better understand the relationship between observed signals and eruptive dynamics.…”

Section: Summary and Perspectivesmentioning

confidence: 99%

The contribution of experimental volcanology to the study of the physics of eruptive processes, and related scaling issues: A review

Roche

Carazzo

2019

Journal of Volcanology and Geothermal Research

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The experimental approach has become a major tool increasingly used by volcanologists in recent decades to investigate the physics of eruptive processes in complement to field and theoretical works. Researchers have developed various methodologies to study volcanic phenomena at reduced length scale. The works involve natural or analogue materials and their types range from first-order tests, to identify fundamental processes and make qualitative comparison with field observations, to more sophisticated experiments in which precise data obtained in a controlled environment can be used to validate outputs of theoretical models. Scaling is a central issue to ensure dynamic similarity between the small-scale experiments and the large-scale volcanic phenomena when natural conditions cannot be simulated due to inherent length scale difference and/or technical limitations. In this respect, dimensionless numbers are used to map physical regimes and to define scaling laws, which allow experimental results to be extrapolated to natural scale. This review presents the variety of experimental studies conducted to investigate subterraneous and aerial volcanic phenomena involving in particular fluid-particle mixtures. We focus on the major scaling issues and the physical regimes investigated, and we also highlight in a historical perspective some of the major advances achieved through experimental studies. Finally we conclude on some perspectives for future works.

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Effects of particle mixtures and nozzle geometry on entrainment into volcanic jets

Cited by 30 publications

References 22 publications

Release characteristics of overpressurised gas from complex vents: implications for volcanic hazards

Release characteristics of overpressurised gas from complex vents: implications for volcanic hazards

Control of Vent Geometry on the Fluid Dynamics of Volcanic Plumes: Insights From Numerical Simulations

The contribution of experimental volcanology to the study of the physics of eruptive processes, and related scaling issues: A review

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