Thermal Liability of Hyaloclastite in the Krafla Geothermal Reservoir, Iceland: The Impact of Phyllosilicates on Permeability and Rock Strength

Weaver, Josh; Eggertsson, Guðjón H.; Utley, James E. P.; Wallace, Paul A. W.; Lamur, Anthony; Kendrick, Jackie E.; Tuffen, Hugh; Markusson, Sigurdur; Lavallée, Yan

doi:10.1155/2020/9057193

Cited by 20 publications

(24 citation statements)

References 94 publications

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“…Volcanoes are constructed over relatively short geological timescales via the accrual of diverse eruptive products that span a porosity range from 0 -97 %, making them inherently unstable structures prone to collapse (Reid et al, 2000;McGuire, 1996;Delaney, 1992). Volcanoes experience deformation due to ongoing magmatic activity (Donnadieu et al, 2001;Voight et al, 1983), pore-fluid pressurisation thanks to active hydrothermal systems and regional tectonics including stress rotation (Reid et al, 2010;Patanè et al, 1994), and alteration due to percolation of fluids (Rosas-Carbajal et al, 2016) and contact with intrusive bodies (Saubin et al, 2019;Weaver et al, 2020). In particular, volcanoes are often located in seismically active regions and may be susceptible to earthquake triggering (Walter et al, 2007;Surono et al, 2012).…”

Section: Rock Failure and Volcano Stabilitymentioning

confidence: 99%

“…Volcanic rocks host void space that ranges from vesicles with complex geometries to networks of elongate cracks or fractures (e.g. Schaefer et al, 2015;Shields et al, 2016;Colombier et al, 2017;Herd and Pinkerton, 1997), and dome lavas in particular frequently have anisotropic pore networks (Heap et al, 2014b;Lavallée and Kendrick, 2020). As porosity is the major control on the strength and geophysical characteristics of geomaterials, such diversity of porosity translates to a broad spectrum of mechanical behaviour of dome rocks and lavas (e.g.…”

Section: Rock Failure and Volcano Stabilitymentioning

confidence: 99%

“…As porosity is the major control on the strength and geophysical characteristics of geomaterials, such diversity of porosity translates to a broad spectrum of mechanical behaviour of dome rocks and lavas (e.g. Harnett et al, 2019a;Heap et al, 2016a;Coats et al, 2018;Lavallée and Kendrick, 2020), and a universal predictor of material strength eludes us. A key parameter in the description of lavas and volcanic rock properties is permeability, which defines materials' ability to build and alleviate pore pressure, important during eruptive activity and quiescence alike (Day, 1996;Saar and Manga, 1999;Mueller et al, 2005;Collinson and Neuberg, 2012;Farquharson et al, 2015;Scheu et al, 2006b).…”

Section: Rock Failure and Volcano Stabilitymentioning

confidence: 99%

“…Heap et al, 2014b, c;Schaefer et al, 2015;Coats et al, 2018;Bubeck et al, 2017;Pappalardo et al, 2017), direct and indirect tensile strength at room or high temperature (Harnett et al, 2019a;Lamur et al, 2018;Hornby et al, 2019;Lamb et al, 2017;Benson et al, 2012) and triaxial tests at varying pressures, temperatures and saturation conditions (Heap et al, 2016a;Smith et al, 2011;Farquharson et al, 2016;Shimada, 1986;Kennedy et al, 2009;Mordensky et al, 2019). Strength of volcanic rocks also typically positively correlates with strain rate (Schaefer et al, 2015;Coats et al, 2018), which in combination with variability in pore geometry, crystallinity and other textural parameters of volcanic rocks ensures that scatter in volcanic rock strength is high (Lavallée and Kendrick, 2020;Heap et al, 2016b). This variability is exacerbated by the effects of pore pressure (Farquharson et al, 2016), in-situ temperature (Coats et al, 2018;Lamur et al, 2018), chemical alteration (Pola et al, 2014;Wyering et al, 2014;Farquharson et al, 2019), thermal stressing (Kendrick et al, 2013;Heap et al, 2014b) and time-dependent (Heap et al, 2011) or cyclic (Schaefer et al, 2015;Benson et al, 2012) stressing, whose impact is contrasting in different volcanic rocks, further enhancing the range of mechanical properties of materials that construct volcanic edifices and lava domes.…”

Section: Rock Failure and Volcano Stabilitymentioning

confidence: 99%

“…We then combine these equations to define the interrelation of each parameter, and to express their evolving relationships as a function of porosity. We limit our analysis to the porosity range examined here (between the 1 st -99 th percentile), and add the caveat that these relationships are likely to be lithologicallydependent due to the textural and microstructural nature of materials (Lavallée and Kendrick, 2020), yet are likely to be broadly applicable to glassy, porphyritic volcanic rocks.…”

Section: Interrelation Of Mechanical Propertiesmentioning

confidence: 99%

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Physical and mechanical rock properties of a heterogeneous volcano; the case of Mount Unzen, Japan

Kendrick¹,

Schaefer²,

Schauroth³

et al. 2020

Preprint

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Abstract. Volcanoes represent one of the most critical geological settings for hazard modelling due to their propensity to both unpredictably erupt and collapse, even in times of quiescence. Volcanoes are heterogeneous at multiple scales, from porosity which is variably distributed and frequently anisotropic to strata that are laterally discontinuous and commonly pierced by fractures and faults. Due to variable and, at times, intense stress and strain conditions during and post-emplacement, volcanic rocks span an exceptionally wide range of physical and mechanical properties. Understanding the constituent materials' attributes is key to improving the interpretation of hazards posed by the diverse array of volcanic complexes. Here, we examine the spectrum of physical and mechanical properties presented by a single dome-forming eruption at a dacitic volcano, Mount Unzen (Japan) by testing a number of isotropic and anisotropic lavas in tension and compression and using monitored acoustic emission (AE) analysis. The lava dome was erupted as a series of 13 lobes between 1991–1995, and its ongoing instability means much of the volcano and its surroundings remain within an exclusion zone today. During a field campaign in 2015, we selected 4 representative blocks as the focus of this study. The core samples from each block span range in porosity from 9.14 to 42.81 %, and permeability ranges from 1.54 × 10−14 to 2.67 × 10−10 m2 (from 1065 measurements). For a given porosity, sample permeability varies by > 2 orders of magnitude is lower for macroscopically anisotropic samples than isotropic samples of similar porosity. An additional 379 permeability measurements on planar block surfaces ranged from 1.90 × 10−15 to 2.58 × 10−12 m2, with a single block having higher standard deviation and coefficient of variation than a single core. Permeability under confined conditions showed that the lowest permeability samples, whose porosity largely comprises microfractures, are most sensitive to effective pressure. The permeability measurements highlight the importance of both scale and confinement conditions in the description of permeability. The uniaxial compressive strength (UCS) ranges from 13.48 to 47.80 MPa, and tensile strength (UTS) using the Brazilian disc method ranges from 1.30 to 3.70 MPa, with crack-dominated lavas being weaker than vesicle-dominated materials of equivalent porosity. UCS is lower in saturated conditions, whilst the impact of saturation on UTS is variable. UCS is between 6.8 and 17.3 times higher than UTS, with anisotropic samples forming each end member. The Young's modulus of dry samples ranges from 4.49 to 21.59 GPa and is systematically reduced in water-saturated tests. The interrelation of porosity, UCS, UTS and Young's modulus was modelled with good replication of the data. Acceleration of monitored acoustic emission (AE) rates during deformation was assessed by fitting Poisson point process models in a Bayesian framework. An exponential acceleration model closely replicated the tensile strength tests, whilst compressive tests tended to have relatively high early rates of AEs, suggesting failure forecast may be more accurate in tensile regimes, though with shorter warning times. The Gutenberg-Richter b-value has a negative correlation with connected porosity for both UCS and UTS tests which we attribute to different stress intensities caused by differing pore networks. b-value is higher for UTS than UCS, and typically decreases (positive Δb) during tests, with the exception of cataclastic samples in compression. Δb correlates positively with connected porosity in compression, and negatively in tension. Δb using a fixed sampling length may be a more useful metric for monitoring changes in activity at volcanoes than b-value with an arbitrary starting point. Using coda wave interferometry (CWI) we identify velocity reductions during mechanical testing in compression and tension, the magnitude of which is greater in more porous samples in UTS but independent of porosity in UCS, and which scales to both b-value and Δb. Yet, saturation obscures velocity changes caused by evolving material properties, which could mask damage accrual or source migration in water-rich environments such as volcanoes. The results of this study highlight that heterogeneity and anisotropy within a single system not only add uncertainty but also have a defining role in the channelling of fluid flow and localisation of strain that dictate a volcano's hazards and the geophysical indicators we use to interpret them.

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Section: Rock Failure and Volcano Stabilitymentioning

confidence: 99%

Section: Rock Failure and Volcano Stabilitymentioning

confidence: 99%

Section: Rock Failure and Volcano Stabilitymentioning

confidence: 99%

Section: Rock Failure and Volcano Stabilitymentioning

confidence: 99%

Section: Interrelation Of Mechanical Propertiesmentioning

confidence: 99%

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Physical and mechanical rock properties of a heterogeneous volcano; the case of Mount Unzen, Japan

Kendrick¹,

Schaefer²,

Schauroth³

et al. 2020

Preprint

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The mechanical behaviour and failure modes of volcanic rocks: a review

2021

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The microstructure and mineralogy of volcanic rocks is varied and complex, and their mechanical behaviour is similarly varied and complex. This review summarises recent developments in our understanding of the mechanical behaviour and failure modes of volcanic rocks. Compiled data show that, although porosity exerts a first-order influence on the uniaxial compressive strength of volcanic rocks, parameters such as the partitioning of the void space (pores and microcracks), pore and crystal size and shape, and alteration also play a role. The presence of water, strain rate, and temperature can also influence uniaxial compressive strength. We also discuss the merits of micromechanical models in understanding the mechanical behaviour of volcanic rocks (which includes a review of the available fracture toughness data). Compiled data show that the effective pressure required for the onset of hydrostatic inelastic compaction in volcanic rocks decreases as a function of increasing porosity, and represents the pressure required for cataclastic pore collapse. Differences between brittle and ductile mechanical behaviour (stress-strain curves and the evolution of porosity and acoustic emission activity) from triaxial deformation experiments are outlined. Brittle behaviour is typically characterised by shear fracture formation, and an increase in porosity and permeability. Ductile deformation can either be distributed (cataclastic pore collapse) or localised (compaction bands) and is characterised by a decrease in porosity and permeability. The available data show that tuffs deform by delocalised cataclasis and extrusive volcanic rocks develop compaction bands (planes of collapsed pores connected by microcracks). Brittle failure envelopes and compactive yield caps for volcanic rocks are compared, highlighting that porosity exerts a first-order control on the stresses required for the brittle-ductile transition and shear-enhanced compaction. However, these data cannot be explained by porosity alone and other microstructural parameters, such as pore size, must also play a role. Compactive yield caps for tuffs are elliptical, similar to data for sedimentary rocks, but are linear for extrusive volcanic rocks. Linear yield caps are considered to be a result of a high pre-existing microcrack density and/or a heterogeneous distribution of porosity. However, it is still unclear, with the available data, why compaction bands develop in some volcanic rocks but not others, which microstructural attributes influence the stresses required for the brittle-ductile transition and shear-enhanced compaction, and why the compactive yield caps of extrusive volcanic rocks are linear. We also review the Young’s modulus, tensile strength, and frictional properties of volcanic rocks. Finally, we review how laboratory data have and can be used to improve our understanding of volcanic systems and highlight directions for future research. A deep understanding of the mechanical behaviour and failure modes of volcanic rock can help refine and develop tools to routinely monitor the hazards posed by active volcanoes.

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Rapid alteration of fractured volcanic conduits beneath Mt Unzen

et al. 2021

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The nature of sub-volcanic alteration is usually only observable after erosion and exhumation at old inactive volcanoes, via geochemical changes in hydrothermal fluids sampled at the surface, via relatively low-resolution geophysical methods or can be inferred from erupted products. These methods are spatially or temporally removed from the real subsurface and thus provide only indirect information. In contrast, the ICDP deep drilling of the Mt Unzen volcano subsurface affords a snapshot into the in situ interaction between the dacitic dykes that fed dome-forming eruptions and the sub-volcanic hydrothermal system, where the most recent lava dome eruption occurred between 1990 and 1995. Here, we analyse drill core samples from hole USDP-4, constraining their degree and type of alteration. We identify and characterize two clay alteration stages: (1) an unusual argillic alteration infill of fractured or partially dissolved plagioclase and hornblende phenocryst domains with kaolinite and Reichweite 1 illite (70)-smectite and (2) propylitic alteration of amphibole and biotite phenocrysts with the fracture-hosted precipitation of chlorite, sulfide and carbonate minerals. These observations imply that the early clay-forming fluid was acidic and probably had a magmatic component, which is indicated for the fluids related to the second chlorite-carbonate stage by our stable carbon and oxygen isotope data. The porosity in the dyke samples is dominantly fracture-hosted, and fracture-filling mineralization is common, suggesting that the dykes were fractured during magma transport, emplacement and cooling, and that subsequent permeable circulation of hydrothermal fluids led to pore clogging and potential partial sealing of the pore network on a timescale of ~ 9 years from cessation of the last eruption. These observations, in concert with evidence that intermediate, crystal-bearing magmas are susceptible to fracturing during ascent and emplacement, lead us to suggest that arc volcanoes enclosed in highly fractured country rock are susceptible to rapid hydrothermal circulation and alteration, with implications for the development of fluid flow, mineralization, stress regime and volcanic edifice structural stability. We explore these possibilities in the context of alteration at other similar volcanoes.

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Thermal Liability of Hyaloclastite in the Krafla Geothermal Reservoir, Iceland: The Impact of Phyllosilicates on Permeability and Rock Strength

Cited by 20 publications

References 94 publications

Physical and mechanical rock properties of a heterogeneous volcano; the case of Mount Unzen, Japan

Physical and mechanical rock properties of a heterogeneous volcano; the case of Mount Unzen, Japan

The mechanical behaviour and failure modes of volcanic rocks: a review

Rapid alteration of fractured volcanic conduits beneath Mt Unzen

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