Predicting Homogeneous Bubble Nucleation in Rhyolite

Hajimirza, Sahand; Gonnermann, H. M.; Gardner, James E.; Giachetti, Thomas

doi:10.1029/2018jb015891

Cited by 30 publications

(62 citation statements)

References 71 publications

(159 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Note that bubble number densities provided in this paper are glass‐referenced and correspond to the number density of both isolated and coalesced bubbles. It represents approximately the total number of bubbles that nucleated during the experiment (see Hajimirza et al , for details about the nucleation process during these experiments).…”

Section: Methodsmentioning

confidence: 99%

Bubble Coalescence and Percolation Threshold in Expanding Rhyolitic Magma

Giachetti

Gonnermann

Gardner

et al. 2019

Geochem Geophys Geosyst

Self Cite

View full text Add to dashboard Cite

Coalescence during bubble nucleation and growth in crystal-free rhyolitic melt was experimentally investigated, and the percolation threshold, defined as the porosity at which the vesicular melt first becomes permeable, was estimated. Experiments with bubble number densities between 10 14 and 10 15 m −3 were compared to four suites of rhyolitic Plinian pumices, which have approximately equal bubble number densities. At the same total porosity, Plinian samples have a higher percentage of coalesced bubbles compared to their experimental counterparts. Percolation modeling of the experimental samples indicates that all of them are impermeable and have percolation thresholds of approximately 80-90%, irrespective of their porosity. Percolation modeling of the Plinian pumices, all of which have been shown to be permeable, gives a percolation threshold of approximately 60%. The experimental samples fall on a distinct trend in terms of connected versus total porosity relative to the Plinian samples, which also have a greater melt-bubble structural complexity. The same holds true for experimental samples of lower bubble number densities. We interpret the comparatively higher coalescence within the Plinian samples to be a consequence of shear deformation of the erupting magma, together with an inherently greater structural complexity resulting from a more complex nucleation process.

show abstract

Section: Methodsmentioning

confidence: 99%

Bubble Coalescence and Percolation Threshold in Expanding Rhyolitic Magma

Giachetti

Gonnermann

Gardner

et al. 2019

Geochem Geophys Geosyst

Self Cite

View full text Add to dashboard Cite

show abstract

“…Explosive volcanic activity is powered by rapid melt degassing of mainly H 2 O, prior to and during fragmentation (e.g., Alidibirov and Dingwell 1996;Gonnermann and Manga 2007). Supersaturation of hydrous silicate melt induced e.g., by decompression drives vesicle formation and growth (e.g., Sparks 1978;Hurwitz and Navon 1994;Mourtada-Bonnefoi and Laporte 2004;Iacono-Marziano et al 2007;Hamada et al 2010;Gardner and Ketcham 2011;Preuss et al 2016;Shea 2017;Hajimirza et al 2019). The number of vesicles per unit volume of melt (VND), and thus the inter-vesicle distance, defines the degassing efficiency (e.g., Toramaru 2006;Allabar and Nowak 2018).…”

Section: Introductionmentioning

confidence: 99%

The effect of initial H2O concentration on decompression-induced phase separation and degassing of hydrous phonolitic melt

Allabar

Gross

Nowak

2020

Contrib Mineral Petrol

View full text Add to dashboard Cite

Supersaturation of H 2 O during magma ascent leads to degassing of melt by formation and growth of vesicles that may power explosive volcanic eruptions. Here, we present experiments to study the effect of initially dissolved H 2 O concentration (c H2Oini ) on vesicle formation, growth, and coalescence in phonolitic melt. Vesuvius phonolitic melts with c H2Oini ranging between 3.3 and 6.3 wt% were decompressed at rates of 1.7 and 0.17 MPa·s −1 and at temperatures ≥ 1323 K. Decompression started from 270 and 200 MPa to final pressures of 150-20 MPa, where samples were quenched isobarically. Optical microscopy and Raman spectroscopic measurements confirm that the glasses obtained were free of microcrystals and Fe-oxide nanolites, implying that the experiments were superliquidus and phase separation of the hydrous melt was homogeneous. A minimum number of the initially formed vesicles, defined by the number density normalized to vesicle-free glass volume (VND), is observed at ~ 5 wt% c H2Oini with a logVND of ~ 5 (in mm −3 ). The logVND increases strongly towards lower and higher c H2Oini by one order of magnitude. Furthermore, an important transition in evolution of vesiculation occurs at ~ 5.6 wt% c H2Oini . At lower c H2Oini , the initial VND is preserved during further decompression up to melt porosities of 30-50%. At higher c H2Oini , the initial vesicle population is erased at low melt porosities of 15-21% during further decompression. This observation is attributed to vesicle coalescence favored by low melt viscosity. In conclusion, c H2Oini determines the VND of initial phase separation and the evolution of vesiculation during decompression that controls the style of volcanic eruptions.

show abstract

“…Thus, Φ melt and c H2O at P final and T d are initially unknown. Nevertheless, the relative importance of H 2 O diffusion during decompression can be determined, which is quantified by the ratio of diffusion timescale τ diff to the timescale of decompression τ d (Hajimirza et al 2019). If the diffusion timescale is shorter than the decompression timescale (τ diff /τ d << 1), near-equilibrium degassing is facilitated and the melt porosity and c H2O prior to quench can be calculated.…”

Section: Quantification Of Melt Porosity Prior To Quenchmentioning

confidence: 99%

Vesicle shrinkage in hydrous phonolitic melt during cooling

Allabar

Dobson

Bauer

et al. 2020

Contrib Mineral Petrol

View full text Add to dashboard Cite

The ascent of hydrous magma prior to volcanic eruptions is largely driven by the formation of H 2 O vesicles and their subsequent growth upon further decompression. Porosity controls buoyancy as well as vesicle coalescence and percolation, and is important when identifying the differences between equilibrium or disequilibrium degassing from textural analysis of eruptive products. Decompression experiments are routinely used to simulate magma ascent. Samples exposed to high temperature (T) and pressure (P) are decompressed and rapidly cooled to ambient T for analysis. During cooling, fluid vesicles may shrink due to decrease of the molar volume of H 2 O and by resorption of H 2 O back into the melt driven by solubility increase with decreasing T at P < 300 MPa. Here, we quantify the extent to which vesicles shrink during cooling, using a series of decompression experiments with hydrous phonolitic melt (5.3-3.3 wt% H 2 O, T between 1323 and 1373 K, decompressed from 200 to 110-20 MPa). Most samples degassed at near-equilibrium conditions during decompression. However, the porosities of quenched samples are significantly lower than expected equilibrium porosities prior to cooling. At a cooling rate of 44 K•s −1 , the fictive temperature T f , where vesicle shrinkage stops, is up to 200 K above the glass transition temperature (T g), Furthermore, decreasing cooling rate enhances vesicles shrinkage. We assess the implications of these findings on previous experimental degassing studies using phonolitic melt, and highlight the importance of correctly interpreting experimental porosity data, before any comparison to natural volcanic ejecta can be attempted.

show abstract

Predicting Homogeneous Bubble Nucleation in Rhyolite

Cited by 30 publications

References 71 publications

Bubble Coalescence and Percolation Threshold in Expanding Rhyolitic Magma

Bubble Coalescence and Percolation Threshold in Expanding Rhyolitic Magma

The effect of initial H2O concentration on decompression-induced phase separation and degassing of hydrous phonolitic melt

Vesicle shrinkage in hydrous phonolitic melt during cooling

Contact Info

Product

Resources

About