Diffusive dehydration and bubble resorption during open-system degassing of rhyolitic melts

Yoshimura, Shumpei; Nakamura, Michihiko

doi:10.1016/j.jvolgeores.2008.01.017

Cited by 26 publications

(35 citation statements)

References 24 publications

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“…The presence of a surface through which a water pressure difference exists, favors diffusion and the development of an outer skin. This has been observed in other samples (Ryan et al, 2015) and is also referred to as bubble-free margin (Yoshimura and Nakamura, 2008). Once the maximum volume is reached when the water in bubble-bubble films has equilibrated, exsolution ceases but bubble coalescence and redistribution can continue internally.…”

Section: Discussionmentioning

confidence: 55%

“…As mass is diffusively removed from the bubbles near to the internal skin margin, they resorb (McIntosh et al, 2014) and surface tension stresses reduce the bubble volume. Therefore, bubbles adjacent to sample edge are progressively consumed by this process and promote the development and thickening of the skin (Figure 1; Yoshimura and Nakamura, 2008).…”

Section: Discussionmentioning

confidence: 99%

“…During vesiculation, bubbles may coalesce and create a variably permeable network that regulates outgassing (Lindoo et al, 2016), which if efficient may result in foam collapse. If outgassing (i.e., the removal of volatiles from the system) is prevented by a low permeability network or barrier (Yoshimura and Nakamura, 2008), pressure may build up and the strain rate at the bubble walls may exceed the inverse of the relaxation time of the melt phase, in which case magma fragments, potentially triggering an explosive eruption (Dingwell, 1996). Collapse of the bubble network is driven by stress (Ashwell et al, 2015), and/or shear (Okumura et al, 2008(Okumura et al, , 2009) and surface tension .…”

Section: Introductionmentioning

confidence: 99%

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Outgassing from Open and Closed Magma Foams

et al. 2017

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During magma ascent, bubbles nucleate, grow, coalesce, and form a variably permeable porous network. The reorganization, failing and sealing of bubble walls may contribute to the opening and closing of the volcanic system. In this contribution we cause obsidian to nucleate and grow bubbles to high gas volume fraction at atmospheric pressure by heating samples to 950 • C for different times and we image the growth through a furnace. Following the experiment, we imaged the internal pore structure of selected samples in 3D and then dissected for analysis of textures and dissolved water content remnant in the glass. We demonstrate that in these high viscosity systems, during foaming and subsequent foam-maturation, bubbles near a free surface resorb via diffusion to produce an impermeable skin of melt around a foam. The skin thickens non-linearly through time. The water concentrations at the outer and inner skin margins reflect the solubility of water in the melt at the partial pressure of water in atmospheric and water-rich bubble conditions, respectively. In this regime, mass transfer of water out of the system is diffusion limited and the sample shrinks slowly. In a second set of experiments in which we polished off the skin of the foamed samples and placed them back in the furnace to allow open system outgassing, we observe rapid sample contraction and collapse of the connected pore network under surface tension as the system efficiently outgasses. In this regime, mass transfer of water is permeability limited. We conclude that diffusion-driven skin formation can efficiently seal connectivity in foams. When rupture of melt film around gas bubbles (i.e., skin removal) occurs, then rapid outgassing and consequent foam collapse modulate gas pressurization in the vesiculated magma. The mechanisms described here are relevant to the evolution of pore network heterogeneity in permeable magmas.

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Section: Discussionmentioning

confidence: 55%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Outgassing from Open and Closed Magma Foams

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“…Local increases in melt H 2 O can result from shear-induced bubble collapse and resorption (Yoshimura & Nakamura, 2008;Watkins et al, 2012), and growth of spherulites (Sparks, 1997;Von Aulock et al, 2013 bubble exsolution and outgassing via bubble networks or fractures (Cabrera et al, 2010;Castro et al, 2012), both of which may conversely lead to a local increase in meteoric water content (e.g., Giachetti & Gonnerman, 2013;Von Aulock et al, 2013).…”

Section: Role Of Heterogeneities On Structural Evolution Of An Obsidimentioning

confidence: 99%

Unravelling textural heterogeneity in obsidian: Shear-induced outgassing in the Rocche Rosse flow

Shields

Mader

Caricchi

et al. 2016

Journal of Volcanology and Geothermal Research

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Obsidian flow emplacement is a complex and understudied aspect of silicic volcanism. Of particular importance is the question of how highly viscous magma can lose sufficient gas in order to erupt effusively as a lava flow. Using an array of methods we study the extreme textural heterogeneity of the Rocche Rosse obsidian flow in Lipari, a 2 km long, 100 m thick,~800 year old lava flow, with respect to outgassing and emplacement mechanisms. 2D and 3D vesicle analyses and density measurements are used to classify the lava into four textural types: 'glassy' obsidian (b15% vesicles), 'pumiceous' lava (N 40% vesicles), high aspect ratio, 'shear banded' lava (20-40% vesicles) and low aspect ratio, 'frothy' obsidian with 30-60% vesicles. Textural heterogeneity is observed on all scales (m to μm) and occurs as the result of strongly localised strain. Magnetic fabric, described by oblate and prolate susceptibility ellipsoids, records high and variable degrees of shearing throughout the flow. Total water contents are derived using both thermogravimetry and infrared spectroscopy to quantify primary (magmatic) and secondary (meteoric) water. Glass water contents are between 0.08-0.25 wt.%. Water analysis also reveals an increase in water content from glassy obsidian bands towards 'frothy' bands of 0.06-0.08 wt.%, reflecting preferential vesiculation of higher water bands and an extreme sensitivity of obsidian degassing to water content. We present an outgassing model that reconciles textural, volatile and magnetic data to indicate that obsidian is generated from multiple shear-induced outgassing cycles, whereby vesicular magma outgasses and densifies through bubble collapse and fracture healing to form obsidian, which then re-vesiculates to produce 'dry' vesicular magma. Repetition of this cycle throughout magma ascent results in the low water contents of the Rocche Rosse lavas and the final stage in the degassing cycle determines final lava porosity. Heterogeneities in lava rheology (vesicularity, water content, microlite content, viscosity) play a vital role in the structural evolution of an obsidian flow and overprint flow-scale morphology. Post-emplacement hydration also depends heavily on local strain, whereby connectivity of vesicles as a result of shear deformation governs sample rehydration by meteoric water, a process previously correlated to lava vesicularity alone.

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“…e.g., Jaupart and Allègre, 1991; Woods and Koyaguchi, 1994;Kozono and Koyaguchi, 2009a, b Okumura et al, 20092 , Verhoogen, 1951Sparks, 1978;, McBirney and Murase, 1970;Alidibirov, 1994;Sugioka and Bursik, 1995;Zhang, 1999;, Papale, 1999 Gon and Rutherford, 2002;Couch, 2003;Couch et al, 2003a, b;Martel andSchmidt, 2003, Suzuki et al, 2007;Hammer, 2008 e.g., Noguchi et al, 2006Noguchi et al, , 2008a Dobson et al, 1989;Taylor, 1991;Villemant and Boudon, 1998;Kusakabe et al, 1999;Nakamura et al, 2008 Multivapor systematics : e.g., Nakamura, 1995a e.g., Sato, 1975;Tsuchiyama, 1985;Nakamura, 1995b;Shimakita, 1998, Rutherford, 2008 Takeuchi and Nakamura 2001 Takeu- (after Newman and Lowenstern, 2002). From these curves, the equilibrium pressure can be estimated from the water content in volcanic glasses (e.g., groundmass glass and glass inclusions), as long as the melt is saturated with volatiles and water dominates the volatile component.…”

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confidence: 99%

Analyses of pyroclastic deposits as a tool for investigating the dynamics of volcanic eruptions

Nakamura¹

2011

Jour. Geol. Soc. Japan

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Recent progress in the science of the products of volcanic eruptions has made it possible to reconstruct past eruption processes on the basis of high-resolution volcanic stratigraphy. Case studies on changing eruption style and related conduit-and magma chamber-processes are helpful in establishing systematic, general patterns for the development of eruptions. They also contribute information towards an eruption mechanism tree that describes bifurcations in eruption processes according to the governing conditions. Methodological progress has been made on various aspects of eruptions, including our understanding of magma-ascent processes in relation to decompression-induced crystallization of groundmass microlites, precise determinations of volatile solubility in silicate melts, the development of analytical methods to measure volatile contents in glass and estimate magma pressure, the accumulation of permeability data, and advances in analytical techniques for rock microstructures (e.g., X-ray microtomography). Given these developments, we can retrieve information on the timescales of eruption dynamics and on the volume of erupted materials from the volcanic stratigraphy.Keywords: pyroclastic deposit, volcanic stratigraphy, pumice, eruption dynamics, degassing, fragmentation Michihiko Nakamura

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Diffusive dehydration and bubble resorption during open-system degassing of rhyolitic melts

Cited by 26 publications

References 24 publications

Outgassing from Open and Closed Magma Foams

Outgassing from Open and Closed Magma Foams

Unravelling textural heterogeneity in obsidian: Shear-induced outgassing in the Rocche Rosse flow

Analyses of pyroclastic deposits as a tool for investigating the dynamics of volcanic eruptions

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