Experiments on gas-ash separation processes in volcanic umbrella plumes

Holasek, Rick E.; Woods, Andrew W.; Self, Stephen

doi:10.1016/0377-0273(95)00054-2

Cited by 62 publications

(52 citation statements)

References 24 publications

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“…[11] The growth of the umbrella cloud is modeled as an axisymmetrical gravity current, spreading out to form a uniform layer at the NBL (the gravity current model) [Holasek et al, 1996b;Sparks et al, 1997]. On the basis of mass conservation law and dimensional analysis, the radius of umbrella cloud R for a volumetric flow rate _ V from below is given as…”

Section: Gravity Current Model Of Umbrella Cloudmentioning

confidence: 99%

“…Holasek et al [1996a] suggested that the value of l ranges from 0.1 to 0.6 from comparisons with laboratory experiments [Holasek et al, 1996b] and field observations [Woods and Kienle, 1994]; however, this range is too wide for the reconstruction of the dynamics of eruption clouds, because the estimate of _ V by equation (2) sensitively depends on the assumed value of l.…”

Section: Dmentioning

confidence: 99%

“…The total height of eruption column, the altitude of NBL and the volumetric flow rate at the NBL are calculated as a function of the mass discharge rate at the vent on the basis of a steady 1-D plume model [Sparks, 1986;Woods, 1988Woods, , 1995. The spreading rate (the increase rate of radius) of umbrella cloud is also calculated from the volumetric flow rate at the NBL on the basis of axisymmetrical gravity current model [Holasek et al, 1996b;Sparks et al, 1997]. These simplified models can run on standard personal computers [Mastin, 2007].…”

Section: Introductionmentioning

confidence: 99%

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A three‐dimensional numerical simulation of spreading umbrella clouds

Suzuki¹,

Koyaguchi²

2009

J. Geophys. Res.

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[1] During explosive volcanic eruptions, an eruption column buoyantly rises as a turbulent plume, and an umbrella cloud spreads laterally as a gravity current at the neutral buoyancy level. The source conditions of explosive eruptions such as mass discharge rates of magma at vents have been estimated from the field observations (e.g., satellite images) on the height of the eruption columns and the spreading rate of umbrella clouds on the basis of the one-dimensional (1-D) plume model and the gravity current model. However, these simplified models contain empirical constants (entrainment coefficient of turbulent plume, k, and Froude number of gravity current, l) that should be justified. We developed a time-dependent three-dimensional (3-D) numerical model of eruption clouds to independently determine the values of these constants. The 3-D model is designed to calculate quantitative features of turbulent mixing between an eruption cloud and the ambient air without any a priori empirical constants by applying a sufficiently fine grid size with a third-order accuracy scheme. It has reproduced the fundamental features of eruption clouds including eruption columns, pyroclastic flows, coignimbrite ash clouds, and umbrella clouds. The altitudes of the spreading umbrella clouds in the 3-D simulations are consistent with those of the neutral buoyancy level of eruption columns estimated by the 1-D plume model with the entrainment coefficient k $ 0.1. The relationship between the volumetric flow rate and the spreading rate of the umbrella cloud in the 3-D simulations is explained by the axisymmetrical gravity current model with l $ 0.2 for eruption clouds in the tropical atmosphere and l $ 0.1 for those in the midlatitude atmosphere. On the other hand, the total column height in the 3-D simulations strongly oscillates even for a constant mass discharge rate, and its time average tends to be substantially greater than the column height estimated by the 1-D plume model with k $ 0.1, particularly for large-scale eruption clouds in the midlatitude atmosphere. We recommend a method to estimate the mass discharge rate from the observation of the column height or the spreading rate of umbrella cloud. The method and the accuracy of the 3-D simulations are tested on the basis of the field data (e.g., the total height of the eruption column, the altitude and the spreading rate of the umbrella cloud, and the mass discharge rate) of the Pinatubo 1991 eruption.

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Section: Gravity Current Model Of Umbrella Cloudmentioning

confidence: 99%

Section: Dmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A three‐dimensional numerical simulation of spreading umbrella clouds

Suzuki¹,

Koyaguchi²

2009

J. Geophys. Res.

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“…The partial mismatch of chemical influence (as indicated in the whole air samples) and ash particle detection during the flight on 16 May 2010 over Northern Ireland and on 19 May over the Norwegian Sea shows a partial separation of volcanic ash and volcanic gases, presumable already close to the volcano eruption column (Holasek et al, 1996), with subsequent somewhat different dispersion due to wind shear. This also means that glazing of aircraft turbines by melting ash and abrasion of aircraft windows does not necessarily occur in the same airspace where enhanced corrosion may occur due to sulphuric acid formed when volcanic SO 2 reacts with atmospheric water.…”

Section: Trace Gases In the Volcanic Cloudsmentioning

confidence: 88%

CARIBIC aircraft measurements of Eyjafjallajökull volcanic clouds in April/May 2010

Rauthe-Schöch¹,

Weigelt

Hermann

et al. 2012

Atmos. Chem. Phys.

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The Civil Aircraft for the Regular Investigation of the Atmosphere Based on an Instrument Container (CARIBIC) project investigates physical and chemical processes in the Earth's atmosphere using a Lufthansa Airbus long-distance passenger aircraft. After the beginning of the explosive eruption of the Eyjafjallajökull volcano on Iceland on 14 April 2010, the first CARIBIC volcano-specific measurement flight was carried out over the Baltic Sea and Southern Sweden on 20 April. Two more flights followed: one over Ireland and the Irish Sea on 16 May and the other over the Norwegian Sea on 19 May 2010. During these three special mission flights the CARIBIC container proved its merits as a comprehensive flying laboratory. The elemental composition of particles collected over the Baltic Sea during the first flight (20 April) indicated the presence of volcanic ash. Over Northern Ireland and the Irish Sea (16 May), the DOAS system detected SO<sub>2</sub> and BrO co-located with volcanic ash particles that increased the aerosol optical depth. Over the Norwegian Sea (19 May), the optical particle counter detected a strong increase of particles larger than 400 nm diameter in a region where ash clouds were predicted by aerosol dispersion models. Aerosol particle samples collected over the Irish Sea and the Norwegian Sea showed large relative enhancements of the elements silicon, iron, titanium and calcium. Non-methane hydrocarbon concentrations in whole air samples collected on 16 and 19 May 2010 showed a pattern of removal of several hydrocarbons that is typical for chlorine chemistry in the volcanic clouds. Comparisons of measured ash concentrations and simulations with the FLEXPART dispersion model demonstrate the difficulty of detailed volcanic ash dispersion modelling due to the large variability of the volcanic cloud sources, extent and patchiness as well as the thin ash layers formed in the volcanic clouds

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“…Despite evidence that the ash and gas components of some plumes may separate, ultimately rising to different altitudes [Holasek et al, 1996b;Seftor et al, 1997], all of these models assume well-mixed plumes where the ash and gas rise confluently. The models describe plumes that initially spread both laterally and vertically at speeds determined by the mass eruption rate of magma from the vent, the exsolved gas content of the erupting magma, and the local vertical wind…”

Section: Introductionmentioning

confidence: 99%