Constraints on cooling rates and permeabilities of pumice in an explosive eruption jet from colour and magnetic mineralogy

Tait, S.; Thomas, Rick; Gardner, James E.; Jaupart, Claude

doi:10.1016/s0377-0273(98)00075-4

Cited by 58 publications

(47 citation statements)

References 13 publications

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“…Such rapid cooling is also predicted to occur in the outer few centimeters of large pumices. These times are very short compared to those needed to oxidize pumices at low temperatures [Tait et al, 1998]. Our model therefore predicts that small pumices and the rims of large ones cool too quickly to oxidize, concurring with observations from the Minoan fall deposit of the differences between small and large pumices.…”

Section: Assumptions and Limitssupporting

confidence: 83%

Constraints on cooling and degassing of pumice during Plinian volcanic eruptions based on model calculations

Hort¹,

Gardner²

2000

J. Geophys. Res.

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Abstract. During explosive volcanic eruptions, pumice clasts are transported into the atmosphere, and their thermal and degassing histories determine how much volatiles are lost syneruptively. This process is studied by combining a steady state eruption column model with a model for the cooling and degassing of pumice. In the model we investigate the impact of various parameters (e.g., mass eruption rate, Blot number, eruption temperature, and geometry) on the cooling and degassing of If this ratio is larger than 50, degassing of the pumice will be nearly complete with a few percent of the original volatiles left in the outer rind of the pumice. For a ratio of less than 0.1 no volatiles escape the pumice. Typical values for thermal and species diffusivity as well as vesicle wall thickness indicate that in the case of degassing C1 and HeO the transition from 0.1 to 50 will be in the pumice size range of 1-10 cm. Here volatile concentration is a strong function of position inside the pumice, suggesting that values for volatile contents measured on picked matrix glass from crushed samples may not be the best way to estimate the volatile content of matrix glass, a number which is frequently used to estimate the total volatile input of volcanic eruptions. This effect is even more pronounced when looking at hydrogen isotopic fractionation with larger pumices tending toward 5D • -120%o and small samples giving 5D > -800/00 .

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Section: Assumptions and Limitssupporting

confidence: 83%

Constraints on cooling and degassing of pumice during Plinian volcanic eruptions based on model calculations

Hort¹,

Gardner²

2000

J. Geophys. Res.

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“…4). Pumice clasts from the Plinian fall deposits span a wide range of bulk vesicularities but have similar permeabilities (0.5-5.0× 10 -12 m 2 ), a permeability range characteristic of pumice from many fall deposits (Klug and Cashman 1996;Gilbert and Sparks 1998;Tait et al 1998;Saar and Manga 1999). By contrast, clast permeability in longtube pumice from the Wineglass Welded Tuff is highly variable (10 -13 to 3×10 -11 m 2 ) over a relatively small range in vesicularity (78-81%), reflecting a strong permeability anisotropy in clasts with highly elongate vesicles.…”

Section: Whole-clast Imagingmentioning

confidence: 99%

“…The extent to which these clasts continue to expand after fragmentation (Thomas et al 1994;Kaminski and Jaupart 1997) is not well constrained. The limited range in pumice permeability observed in Plinian fall deposits (~10 -12 m 2 ; Klug and Cashman 1996;Tait et al 1998) suggests that preservation, rather than disruption, of larger clasts may require that a threshold permeability be reached. Fine ash (<63 µm) may result from rapid decompression of individual overpressured bubbles (Sparks 1978) or by pulverization of quenched clasts within the conduit (Kaminski and Jaupart 1998).…”

Section: Introductionmentioning

confidence: 99%

Structure and physical characteristics of pumice from the climactic eruption of Mount Mazama (Crater Lake), Oregon

Klug

Cashman

Bacon

2002

Bulletin of Volcanology

213

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The vesicularity, permeability, and structure of pumice clasts provide insight into conditions of vesiculation and fragmentation during Plinian fall and pyroclastic flow-producing phases of the ~7,700 cal. year B.P. climactic eruption of Mount Mazama (Crater Lake), Oregon. We show that bulk properties (vesicularity and permeability) can be correlated with internal textures and that the clast structure can be related to inferred changes in eruption conditions. The vesicularity of all pumice clasts is 75-88%, with >90% interconnected pore volume. However, pumice clasts from the Plinian fall deposits exhibit a wider vesicularity range and higher volume percentage of interconnected vesicles than do clasts from pyroclastic-flow deposits. Pumice permeabilities also differ between the two clast types, with pumice from the fall deposit having higher minimum permeabilities (~5×10 -13 m 2 ) and a narrower permeability range (5-50×10 -13 m 2 ) than clasts from pyroclastic-flow deposits (0.2-330×10 -13 m 2 ). The observed permeability can be modeled to estimate average vesicle aperture radii of 1-5 µm for the fall deposit clasts and 0.25-1 µm for clasts from the pyroclastic flows. High vesicle number densities (~10 9 cm -3 ) in all clasts suggest that bubble nucleation occurred rapidly and at high supersaturations. Post-nucleation modifications to bubble populations include both bubble growth and coalescence. A single stage of bubble nucleation and growth can account for 35-60% of the vesicle population in clasts from the fall deposits, and 65-80% in pumice from pyroclastic flows. Large vesicles form a separate population which defines a power law distribution with fractal dimension D=3.3 (range 3.0-3.5). The large D value, coupled with textural evidence, suggests that the large vesicles formed primarily by coalescence. When viewed together, the bulk properties (vesicularity, permeability) and textural characteristics of all clasts indicate rapid bubble nucleation followed by bubble growth, coalescence and permeability development. This sequence of events is best explained by nucleation in response to a downward-propagating decompression wave, followed by rapid bubble growth and coalescence prior to magma disruption by fragmentation. The heterogeneity of vesicle sizes and shapes, and the absence of differential expansion across individual clasts, suggest that post-fragmentation expansion played a limited role in the development of pumice structure. The higher vesicle number densities and lower permeabilities of pyroclastic-flow clasts indicate limited coalescence and suggest that fragmentation occurred shortly after decompression. Either increased eruption velocities or increased depth of fragmentation accompanying caldera collapse could explain compression of the pre-fragmentation vesiculation interval.Editorial responsibility: M. Rosi

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“…Hort and Gardner (2000) discuss the assumptions and limitations of that modeling pumice cooling, one of which is the assumption of conductive cooling. They showed, however, that model results match the observations of Tait et al (1998) for the rate of oxidation of pumice, which occurs only in high temperature pumice. Note: Lipari = powder of Lipari obsidian; Phonolite = powder of Laacher See phonolite; Rhyodacite = powder of Minoan rhyodacite.…”

Section: Discussionmentioning

confidence: 86%

Experimental and model constraints on degassing of magma during ascent and eruption

Gardner¹,

Burgisser²,

Hort³

et al. 2006

Neogene-Quaternary Continental Margin Volcanism: A Perspective From Me´xico

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Surface volcanic gases may reflect volatile budgets of magma and forecast impending eruptions, and their release to the atmosphere may affect climate. The dynamics of magma degassing is complicated, however, by differences in the solubility, partitioning, and diffusion of the various volatiles, all of which can vary with pressure, temperature, and melt composition. To constrain possible gas outputs, we carried out experiments to determine how Cl partitions between water bubbles and silicate melt, and decompression experiments to examine how Cl behaves duringclosed-and open-system degassing. We incorporate our findings and those from the literature for CO 2 and S into a steady, isothermal, and homogeneous flow model to estimate fluxes of gases at the vent from ascending water-rich magma, assuming different scenarios for the onset and development of permeability in bubbly magma. We find that, for given permeability scenarios, total gas fluxes vary with magma flux, but ratios of gas species do not change. The S/Cl and SO 2 /CO 2 ratios do change, however, depending on whether the magma is oxidized or reduced. After magma fragments into a Plinian eruption column gases continue to escape from cooling pumice in the plume, but here the rate of gas release is controlled by diffusion, which varies with temperature.Degassing of pumice and ash was modeled by linking a steady-state plume model, which gives the vertical variation of mean temperature and velocity of particles inside the plume, to a conductive cooling model of pumices, which controls diffusion of Cl, CO 2 , and S in pumice. We find that gas loss increases with column height (mass flux) and initial temperature, because in both cases pumices cool over a longer time period, allowing more gas to diffuse out of the matrix glass. The amount of gas released also depends on the size distribution of particles in the erupting mixture, with less being released for a finely skewed distribution.

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Constraints on cooling rates and permeabilities of pumice in an explosive eruption jet from colour and magnetic mineralogy

Cited by 58 publications

References 13 publications

Constraints on cooling and degassing of pumice during Plinian volcanic eruptions based on model calculations

Constraints on cooling and degassing of pumice during Plinian volcanic eruptions based on model calculations

Structure and physical characteristics of pumice from the climactic eruption of Mount Mazama (Crater Lake), Oregon

Experimental and model constraints on degassing of magma during ascent and eruption

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