Reconciling bubble nucleation in explosive eruptions with geospeedometers

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

doi:10.1038/s41467-020-20541-1

Cited by 35 publications

(38 citation statements)

References 70 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Bubble sizes and number density reflect ascent rates and conditions (e.g., Toramaru, 2006;Hajimirza et al, 2021). Embayments almost always preserve low bubble number densities and sizes.…”

Section: Discussionmentioning

confidence: 99%

“…The textures can be interpreted to infer processes in the subsurface that are not directly observable, including pre-eruptive magmatic storage, magmatic ascent, and fragmentation (e.g., Toramaru, 2006Toramaru, , 2008Rutherford, 2008;Gardner et al, 2017). Some textures can be used as geospeedometers because they preserve information about the rates and timescales over which processes occur (e.g., Cashman, 1992;Pamukcu et al, 2015;Hajimirza et al, 2021).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Implications of Multiple Disequilibrium Textures in Quartz-Hosted Embayments

et al. 2021

View full text Add to dashboard Cite

The faces of volcanic phenocrysts may be marked by imperfections occurring as holes that penetrate the crystal interior. When filled with glass these features, called embayments or reentrants, have been used to petrologically constrain magmatic ascent rate. Embayment ascent speedometry relies on the record of disequilibrium preserved as diffusion-limited volatile concentration gradients in the embayment glass. Clear, glassy embayments are carefully selected for speedometry studies. The use and subsequent descriptions of pristine embayments overrepresent their actual abundance. Here, we provide a textural analysis of the number, morphology, and filling characteristics of quartz-hosted embayments. We target a collection of large (i.e., >20 km3 erupted volume) silicic eruptions, including the Bishop Tuff, Tuff of Bluff Point, Bandelier Tuff, Mesa Falls Tuff, and Huckleberry Ridge Tuff in the United States, Oruanui Tuff in New Zealand, Younger Toba Tuff in Indonesia, the Kos Plateau Tuff in Greece, and the Giant Pumice from La Primavera caldera in Mexico. For each unit, hundreds of quartz crystals were picked and the total number of embayment-hosting crystals were counted and categorized into classifications based on the vesicularity and morphology. We observed significant variability in embayment abundance, form, and vesicularity across different eruptions. Simple, cylindrical forms are the most common, as are dense glassy embayments. Increasingly complex shapes and a range of bubble textures are also common. Embayments may crosscut or deflect prominent internal cathodoluminescence banding in the host quartz, indicating that embayments form by both dissolution and growth. We propose potential additional timescales recorded by embayment disequilibrium textures, namely, faceting, bubbles, and the lack thereof. Embayment formation likely occurs tens to hundreds of years before eruption because embayment surfaces are rounded instead of faceted. Bubble textures in embayments are far from those predicted by equilibrium solubility. Homogenous nucleation conditions likely allow preservation of pressures much greater than magmastatic inside embayments. Our textural observations lend insight into embayment occurrence and formation and guide further embayment studies.

show abstract

“…Bubble sizes and number density reflect ascent rates and conditions (e.g., Toramaru, 2006;Hajimirza et al, 2021). Embayments almost always preserve low bubble number densities and sizes.…”

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Implications of Multiple Disequilibrium Textures in Quartz-Hosted Embayments

et al. 2021

View full text Add to dashboard Cite

show abstract

“…In contrast, some of the smallest isolated vesicles are moderately spherical. The contorted vesicle network shape and the abundance of microlites between vesicles could hinder diffusion of the remaining dissolved volatiles to existing bubbles, enabling heterogeneous nucleation on microlites and leading to the formation of the disconnected group of bubbles (Hajimirza et al 2021). We interpret that the population of small, isolated vesicles (~ 1% of vesicularity; Fig.…”

Section: Vesicle Network Analysismentioning

confidence: 91%

Mafic explosive volcanism at Llaima Volcano: 3D x-ray microtomography reconstruction of pyroclasts to constrain shallow conduit processes

et al. 2021

View full text Add to dashboard Cite

Mafic volcanic activity is dominated by effusive to mildly explosive eruptions. Plinian and ignimbrite-forming mafic eruptions, while rare, are also possible; however, the conditions that promote such explosivity are still being explored. Eruption style is determined by the ability of gas to escape as magma ascends, which tends to be easier in low-viscosity, mafic magmas. If magma permeability is sufficiently high to reduce bubble overpressure during ascent, volatiles may escape from the magma, inhibiting violent explosive activity. In contrast, if the permeability is sufficiently low to retain the gas phase within the magma during ascent, bubble overpressure may drive magma fragmentation. Rapid ascent may induce disequilibrium crystallization, increasing viscosity and affecting the bubble network with consequences for permeability, and hence, explosivity. To explore the conditions that promote strongly explosive mafic volcanism, we combine microlite textural analyses with synchrotron x-ray computed microtomography of 10 pyroclasts from the 12.6 ka mafic Curacautín Ignimbrite (Llaima Volcano, Chile). We quantify microlite crystal size distributions (CSD), microlite number densities, porosity, bubble interconnectivity, bubble number density, and geometrical properties of the porous media to investigate the role of magma degassing processes at mafic explosive eruptions. We use an analytical technique to estimate permeability and tortuosity by combing the Kozeny-Carman relationship, tortuosity factor, and pyroclast vesicle textures. The groundmass of our samples is composed of up to 44% plagioclase microlites, > 85% of which are < 10 µm in length. In addition, we identify two populations of vesicles in our samples: (1) a convoluted interconnected vesicle network produced by extensive coalescence of smaller vesicles (> 99% of pore volume), and (2) a population of very small and completely isolated vesicles (< 1% of porosity). Computed permeability ranges from 3.0 × 10−13 to 6.3 × 10−12 m2, which are lower than the similarly explosive mafic eruptions of Tarawera (1886; New Zealand) and Etna (112 BC; Italy). The combination of our CSDs, microlite number densities, and 3D vesicle textures evidence rapid ascent that induced high disequilibrium conditions, promoting rapid syn-eruptive crystallization of microlites within the shallow conduit. We interpret that microlite crystallization increased viscosity while simultaneously forcing bubbles to deform as they grew together, resulting in the permeable by highly tortuous network of vesicles. Using the bubble number densities for the isolated vesicles (0.1-3−3 × 104 bubbles per mm3), we obtain a minimum average decompression rate of 1.4 MPa/s. Despite the textural evidence that the Curacautín magma reached the percolation threshold, we propose that rapid ascent suppressed outgassing and increased bubble overpressures, leading to explosive fragmentation. Further, using the porosity and permeability of our samples, we estimated that a bubble overpressure > 5 MPa could have been sufficient to fragment the Curacautín magma. Other mafic explosive eruptions report similar disequilibrium conditions induced by rapid ascent rate, implying that syn-eruptive disequilibrium conditions may control the explosivity of mafic eruptions more generally.

show abstract

“…Assuming disequilibrium degassing, rhyolitic melt viscosity at fragmentation is ∼10 6 Pa•s (Gonnermann and Houghton, 2012;Hajimirza et al, 2021), a reasonable value for a wide range of silicic magmas (Gardner et al, 1996). For a surface tension of ∼0.2 N/m (Bagdassarov et al, 2000) and in the absence of confining pressure, R = ∼10 −5 m protopyroclasts can sinter above the fragmentation zone within ∼50 s, prior to quench (Equation 1).…”

Section: Sintering Of Protopyroclastsmentioning

confidence: 99%

The products of primary magma fragmentation finally revealed by pumice agglomerates

Giachetti

Trafton

Wiejaczka

et al. 2021

Geology

Self Cite

View full text Add to dashboard Cite

Following rapid decompression in the conduit of a volcano, magma breaks into ash- to block-sized fragments, powering explosive sub-Plinian and Plinian eruptions that may generate destructive pyroclastic falls and flows. It is thus crucial to assess how magma breaks up into fragments. This task is difficult, however, because of the subterranean nature of the entire process and because the original size of pristine fragments is modified by secondary fragmentation and expansion. New textural observations of sub-Plinian and Plinian pumice lapilli reveal that some primary products of magma fragmentation survive by sintering together within seconds of magma break-up. Their size distributions reflect the energetics of fragmentation, consistent with products of rapid decompression experiments. Pumice aggregates thus offer a unique window into the previously inaccessible primary fragmentation process and could be used to determine the potential energy of fragmentation.

show abstract

Reconciling bubble nucleation in explosive eruptions with geospeedometers

Cited by 35 publications

References 70 publications

Implications of Multiple Disequilibrium Textures in Quartz-Hosted Embayments

Implications of Multiple Disequilibrium Textures in Quartz-Hosted Embayments

Mafic explosive volcanism at Llaima Volcano: 3D x-ray microtomography reconstruction of pyroclasts to constrain shallow conduit processes

The products of primary magma fragmentation finally revealed by pumice agglomerates

Contact Info

Product

Resources

About