Impact of reduced near‐field entrainment of overpressured volcanic jets on plume development

Saffaraval, Farhad; Solovitz, Stephen A.; Ogden, D. E.; Mastin, Larry G.

doi:10.1029/2011jb008862

Cited by 23 publications

(18 citation statements)

References 37 publications

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“…This hypothesis is based on the self‐similarity of pure jets or plumes (e.g., Batchelor, ). On the other hand, because eruption columns are not self‐similar, the value of k varies considerably with height (e.g., Carazzo et al, ; Kaminski et al, ; Saffaraval et al, ; Suzuki & Koyaguchi, ). Here we calculate the values of Q in ,

\overset{v}{true}

, and

\overset{r}{true}

from the 3‐D simulations without gravity using equations and (see Appendix B) and determine k as a function of height (cf.…”

Section: Results Of 3‐d Simulations Without Gravitymentioning

confidence: 99%

The Condition of Eruption Column Collapse: 2. Three‐Dimensional Numerical Simulations of Eruption Column Dynamics

et al. 2018

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The scenarios leading to column collapse during explosive volcanic eruptions are diverse because of their complex dependence on geological and petrological factors. In a companion paper, we proposed a reference model to predict column collapse condition on the basis of analytical solutions of one‐dimensional eruption models. Here we perform three‐dimensional (3‐D) simulations of eruption column dynamics to confirm the reference model. In the 3‐D simulations, the velocity and pressure boundary conditions at the crater top are determined from quasi‐1‐D conduit flow. When a gas‐pyroclast mixture erupts from a conduit‐crater system that satisfies the conditions of choked flow at the crater base or top, the mixture exits as either an underexpanded (overpressured) or overexpanded (underpressured) jet. The 3‐D simulations show that the underexpanded jets are accelerated and the overexpanded jets are decelerated due to decompression‐compression processes just above the vent. The total momentum flux after these decompression‐compression processes measured in the 3‐D simulations agrees well with the values estimated using the reference model. The column collapse condition determined by the 3‐D simulations is consistent with the reference model, with an effective entrainment coefficient of k = 0.05. We also find that complex flow patterns in the transitional state of column collapse result from multidimensional compressible fluid dynamical and buoyancy effects.

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\overset{v}{true}

, and

\overset{r}{true}

from the 3‐D simulations without gravity using equations and (see Appendix B) and determine k as a function of height (cf.…”

Section: Results Of 3‐d Simulations Without Gravitymentioning

confidence: 99%

The Condition of Eruption Column Collapse: 2. Three‐Dimensional Numerical Simulations of Eruption Column Dynamics

et al. 2018

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“…As we simulated smaller‐scale eruptions (

{\overset{m}{true}}_{0} =

2.51×10 6 kg s −1 ) than these previous studies, we infer that there is some specific mechanism that suppresses entrainment around volcanic plumes/jets as the magma discharge rate decreases. In addition to these mechanisms, it has also been suggested that the entrainment can be suppressed in supersonic flows [ Saffaraval et al , ; Suzuki and Koyaguchi , ]. To better constrain the values of k for volcanic plumes/jets over a wide range of eruption conditions, more comprehensive parameter studies using 3‐D numerical simulations including supersonic flow would be necessary.…”

Section: Estimation Of Entrainment Efficiencymentioning

confidence: 99%

Effects of wind on entrainment efficiency in volcanic plumes

Suzuki

Koyaguchi

2015

JGR Solid Earth

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The entrainment of air by turbulent mixing plays a central role in the dynamics of volcanic eruption clouds, as the amount of entrained air controls the height of the plume. In one‐dimensional models of volcanic plumes, the efficiency of entrainment under a wind field is parameterized using two empirical constants. The first is the coefficient associated with the entrainment caused by the shear between the volcanic plume and the ambient air (i.e., the radial entrainment coefficient), and the other is associated with the entrainment caused by wind (i.e., the wind entrainment coefficient). In this study, we used three‐dimensional numerical simulations of volcanic plumes to determine the effective values of these empirical constants from the relationship between eruption conditions and plume heights. These simulations suggest that the value of the radial entrainment coefficient is 0.05–0.06, which is slightly smaller than that of pure jets or plumes seen in laboratory experiments (0.07–0.15). The value of the wind entrainment coefficient was estimated to be 0.1–0.3, which is significantly smaller than those estimated from laboratory experiments (0.3–1.0). The entrainment coefficients derived from these simulations successfully explain the observations made during the 2011 Shinmoe‐dake eruptions in which the volcanic plumes were significantly distorted by the wind.

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“…This assumption is appropriate for slender plumes (Morton et al, 1956;Woods, 1988;Linden, 2000), where the length scale of radial variations is much smaller than the length scale for vertical variations. The assumption may not be appropriate very near to the vent, where the erupted material can have a substantial over-pressure (Woods and Bower, 1995;Ogden et al, 2008b;Saffaraval et al, 2012). This alters the flow dynamics (Woods and Bower, 1995;Ogden et al, 2008b,a), in particular the turbulent mixing processes, such that a different parameterization of entrainment is required (Saffaraval et al, 2012).…”

Section: The Plumerise Model Of Moist Wind-blown Volcanic Plumesmentioning

confidence: 99%

“…The assumption may not be appropriate very near to the vent, where the erupted material can have a substantial over-pressure (Woods and Bower, 1995;Ogden et al, 2008b;Saffaraval et al, 2012). This alters the flow dynamics (Woods and Bower, 1995;Ogden et al, 2008b,a), in particular the turbulent mixing processes, such that a different parameterization of entrainment is required (Saffaraval et al, 2012). However, the pressure in the near vent jet rapidly adjusts to atmospheric pressure (Saffaraval et al, 2012) and therefore we expect the model results to be little affected by the simplified description (Saffaraval et al, 2012).…”

Section: The Plumerise Model Of Moist Wind-blown Volcanic Plumesmentioning

confidence: 99%

A global sensitivity analysis of the PlumeRise model of volcanic plumes

Woodhouse

Hogg

Phillips

2016

Journal of Volcanology and Geothermal Research

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Integral models of volcanic plumes allow predictions of plume dynamics to be made and the rapid estimation of volcanic source conditions from observations of the plume height by model inversion. Here we introduce PlumeRise, an integral model of volcanic plumes that incorporates a description of the state of the atmosphere, includes the effects of wind and the phase change of water, and has been developed as a freely available web-based tool. The model can be used to estimate the height of a volcanic plume when the source conditions are specified, or to infer the strength of the source from an observed plume height through a model inversion. The predictions of the volcanic plume dynamics produced by the model are analysed in four case studies in which the atmospheric conditions and the strength of the source are varied. A global sensitivity analysis of the model to a selection of model inputs is performed and the results are analysed using parallel coordinate plots for visualisation and variance-based sensitivity indices to quantify the sensitivity of model outputs. We find that if the atmospheric conditions do not vary widely then there is a small set of model inputs that strongly influence the model predictions. When estimating the height of the plume, the source mass flux has a controlling influence on the model prediction, while variations in the plume height strongly effect the inferred value of the source mass flux when performing inversion studies. The values taken for the entrainment coefficients have a particularly important effect on the quantitative predictions. The dependencies of the model outputs to variations in the inputs are discussed and compared to simple algebraic expressions that relate source conditions to the height of the plume.

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Impact of reduced near‐field entrainment of overpressured volcanic jets on plume development

Cited by 23 publications

References 37 publications

The Condition of Eruption Column Collapse: 2. Three‐Dimensional Numerical Simulations of Eruption Column Dynamics

The Condition of Eruption Column Collapse: 2. Three‐Dimensional Numerical Simulations of Eruption Column Dynamics

Effects of wind on entrainment efficiency in volcanic plumes

A global sensitivity analysis of the PlumeRise model of volcanic plumes

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