The role of melt-fracture degassing in defusing explosive rhyolite eruptions at volcán Chaitén

Castro, Jonathan M.; Cordonnier, B.; Tuffen, Hugh; Tobin, Mark J.; Puškar, Ljiljana; Martin, Michael; Bechtel, Hans A.

doi:10.1016/j.epsl.2012.04.024

Cited by 130 publications

(201 citation statements)

References 34 publications

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“…We also see evidence for outgassing via shear-induced fracture and healing of the melt, also observed during shearing of analogue silicic magma samples (Okumura et al, 2010;Shields et al, 2014) and in natural samples (e.g., (Stasiuk et al, 1996;Tuffen et al, 2003;Castro et al, 2012;Cabrera et al, n.d.). Fig.…”

Section: Effect Of Shear On Obsidian Degassing and Outgassingmentioning

confidence: 93%

“…Early work by (Eichelberger et al, 1986) suggested that silicic magma rises as a highly permeable foam which, upon extrusion, loses gas via development of bubble connectivity, enabling outgassing to the conduit walls (Jaupart & Allegre, 1991). Another body of work describes shear-induced fracturing of magma, leading to permeable pathways through which volatiles can escape (Stasiuk et al, 1996;Gonnerman & Manga, 2003;Okumura et al, 2009;Cabrera et al, 2010;Castro et al, 2012). There is widespread evidence for this non-explosive magma fragmentation, in the form of brittle fracture and healing.…”

Section: Effusive Silicic Volcanismmentioning

confidence: 99%

“…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%

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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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Section: Effect Of Shear On Obsidian Degassing and Outgassingmentioning

confidence: 93%

Section: Effusive Silicic Volcanismmentioning

confidence: 99%

Section: Role Of Heterogeneities On Structural Evolution Of An Obsidimentioning

confidence: 99%

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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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“…During fragmentation and production of the tuffisitic material, stress is released through fracturing (instead of allowing for a build up of stress leading to eruption), which in turn allows gases to escape (Castro et al, 2012), at least for the time it takes to recover host rock values of permeability. In this manner, the formation of tuffisites may actually retard an eruption and perhaps lessen its explosivity.…”

Section: Discussionmentioning

confidence: 99%

“…The fragmental origin of tuffisites might suggest that their formation will increase the porosity and permeability (Castro et al, 2012) and reduce the strength (Paterson and Wong, (Tuffen et al, 2003) and up to more than 500 meters depth (Heiken et al, 1988) 2005) of otherwise competent host rock. Ultimately, the strength of the conduit-filling material and the permeability of the volcanic edifice are likely to be key properties governing both eruption style (effusive or explosive (Collinson and Neuberg, 2012;Kennedy et al, 2010)) and dynamics (catastrophic or continuous; Taisne and Jaupart (2008)).…”

Section: The Host Rock Seems Tuffisized Ie Infiltrated By the Tuffmentioning

confidence: 99%

Strength and permeability recovery of tuffisite-bearing andesite

Kolzenburg

Heap

Lavallée³

et al. 2012

Solid Earth

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Abstract. Tuffisites, the products of subsurface fragmentation, transport and deposition, are common in explosive volcanic environments. Their study provides direct insight to the mechanical processes operating within volcanic conduits. Here we document the influence of the presence of coherent tuffisite veins on the physical properties of andesitic rocks. We find that (1) compressive strength is unaffected by the presence and/or orientation of tuffisites, (2) permeability doubles when tuffisites are oriented favorably (at 45 • to the fluid flow direction), and (3) ultrasonic wave velocities show a continuous increase with depth, independent of vein presence and orientation. Although the influence of tuffisites on andesitic rock properties determined here is modest, we emphasize that the material tested represents the post-eruptive state of tuffisite. Thus, these results likely delineate the upper and lower boundaries of strength vs. permeability and porosity, respectively. Our evidence suggests that, via compaction and lithification, tuffisites may restore the strength of the volcanic host-rocks to that of their pre-tuffisite values.

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Volcanic sintering: Timescales of viscous densification and strength recovery

Vasseur

Wadsworth

Lavallée

et al. 2013

Geophysical Research Letters

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[1] Sintering and densification are ubiquitous processes influencing the emplacement of both effusive and explosive products of volcanic eruptions. Here we sinter ash-size fragments of a synthetic National Institute of Standards and Technology viscosity standard glass at temperatures at which the resultant melt has a viscosity of ∼108–109 Pa.s at 1bar to assess sintering dynamics under near-surface volcanic conditions. We track the strength recovery via uniaxial compressive tests. We observe that volcanic ash sintering is dominantly time dependent, temperature dependent, and grain size dependent and may thus be interpreted to be controlled by melt viscosity and surface tension. Sintering evolves from particle agglutination to viscous pore collapse and is accompanied by a reduction in connected porosity and an increase in isolated pores. Sintering and densification result in a nonlinear increase in strength. Micromechanical modeling shows that the pore-emanated crack model explains the strength of porous lava as a function of pore fraction and size.

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The role of melt-fracture degassing in defusing explosive rhyolite eruptions at volcán Chaitén

Cited by 130 publications

References 34 publications

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

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

Strength and permeability recovery of tuffisite-bearing andesite

Volcanic sintering: Timescales of viscous densification and strength recovery

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