The porosity of pyroclasts as an indicator of volcanic explosivity

Mueller, S.; Scheu, Bettina; Kueppers, Ulrich; Spieler, O.; Richard, Dominique; Dingwell, Donald B.

doi:10.1016/j.jvolgeores.2011.04.006

Cited by 60 publications

(52 citation statements)

References 21 publications

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“…Intrusive rocks have little initial porosity due to their holocrystalline matrix, but their post-cooling porosity and permeability develops as a result of tectonic and thermal stresses that manifest as macroscopic and microscopic fractures (Géraud 1994;Lane and Gilbert 2008). Volcanic rocks have a wide range of porosities due to variables such as cooling time, transport, gas content, and weathering (e.g., Mueller et al 2011;Olalla et al 2010), while porosity in volcaniclastic and sedimentary rocks is generally controlled by the size and distribution of particles (e.g., Heap et al 2017a;Bai et al 2016).…”

Section: Microfracture and Pore Analysismentioning

confidence: 99%

Matrix permeability of reservoir rocks, Ngatamariki geothermal field, Taupo Volcanic Zone, New Zealand

et al. 2018

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The Taupo Volcanic Zone (TVZ) hosts 23 geothermal fields, seven of which are currently utilised for power generation. Ngatamariki geothermal field (NGF) is one of the latest geothermal power generation developments in New Zealand (commissioned in 2013), located approximately 15 km north of Taupo. Samples of reservoir rocks were taken from the Tahorakuri Formation and Ngatamariki Intrusive Complex, from five wells at the NGF at depths ranging from 1354 to 3284 m. The samples were categorised according to whether their microstructure was pore or microfracture dominated. Image analysis of thin sections impregnated with an epoxy fluorescent dye was used to characterise and quantify the porosity structures and their physical properties were measured in the laboratory. Our results show that the physical properties of the samples correspond to the relative dominance of microfractures compared to pores. Microfracture-dominated samples have low connected porosity and permeability, and the permeability decreases sharply in response to increasing confining pressure. The pore-dominated samples have high connected porosity and permeability, and lower permeability decrease in response to increasing confining pressure. Samples with both microfractures and pores have a wide range of porosity and relatively high permeability that is moderately sensitive to confining pressure. A general trend of decreasing connected porosity and permeability associated with increasing dry bulk density and sonic velocity occurs with depth; however, variations in these parameters are more closely related to changes in lithology and processes such as dissolution and secondary veining and re-crystallisation. This study provides the first broad matrix permeability characterisation of rocks from depth at Ngatamariki, providing inputs for modelling of the geothermal system. We conclude that the complex response of permeability to confining pressure is in part due to the intricate dissolution, veining, and recrystallization textures of many of these rocks that lead to a wide variety of pore shapes and sizes. While the laboratory results are relevant only to similar rocks in the Taupo Volcanic Zone, the relationships they highlight are applicable to other geothermal fields, as well as rock mechanic applications to, for example, aspects of volcanology, landslide stabilisation, mining, and tunnelling at depth.

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Section: Microfracture and Pore Analysismentioning

confidence: 99%

Matrix permeability of reservoir rocks, Ngatamariki geothermal field, Taupo Volcanic Zone, New Zealand

et al. 2018

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“…Insights into the interacting variables are preserved in the crystal and pore textures of the lava and further supplemented by compositional analysis and observations during eruption. At dome volcanoes, the volatile content, and consequently bubbles, are considered particularly important as the system is often on the boundary between explosive and effusive behavior (e.g., Edmonds and Herd, 2007;Mueller et al, 2011).…”

Section: Introductionmentioning

confidence: 99%

Textural Insights Into the Evolving Lava Dome Cycles at Santiaguito Lava Dome, Guatemala

et al. 2018

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The structures and textures preserved in lava domes reflect underlying magmatic and eruptive processes, and may provide evidence of how eruptions initiate and evolve. This study explores the remarkable cycles in lava extrusion style produced between 1922 and 2012 at the Santiaguito lava dome complex, Guatemala. By combining an examination of eruptive lava morphologies and textures with a review of historical records, we aim to constrain the processes responsible for the range of erupted lava type and morphologies. The Santiaguito lava dome complex is divided into four domes (El Caliente, La Mitad, El Monje, El Brujo), containing a range of proximal structures (e.g., spines) from which a series of structurally contrasting lava flows originate. Vesicular lava flows (with a'a like, yet non-brecciated flow top) have the highest porosity with interconnected spheroidal pores and may transition into blocky lava flows. Blocky lava flows are high volume and texturally variable with dense zones of small tubular aligned pore networks and more porous zones of spheroidal shaped pores. Spines are dense and low volume and contain small skeletal shaped pores, and subvertical zones of sigmoidal pores. We attribute the observed differences in pore shapes to reflect shallow inflation, deflation, flattening, or shearing of the pore fraction. Effusion rate and duration of the eruption define the amount of time available for heating or cooling, degassing and outgassing prior to and during extrusion, driving changes in pore textures and lava type. Our new textural data when reviewed with all the other published data allow a cyclic model to be developed. The cyclic eruption models are influenced by viscosity changes resulting from (1) initial magmatic composition and temperature, and (2) effusion rate which in turn affects degassing, outgassing and cooling time in the conduit. Each lava type presents a unique set of hazards and understanding the morphologies and dome progression is useful in hazard forecasting.

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“…7b ≤ k ≤ 10 −13 m 2 ) might partially explain why the modal porosity of large datasets of edifice-forming material tends to fall between 0.10 and 0.20 (e.g. Mueller et al, 2011;Bernard et al, 2015;Farquharson et al, 2015;Lavallée et al, 2017).…”

Section: A Limit To Compaction and Permeability Reductionmentioning

confidence: 99%

“…Mueller et al, 2011), heterogeneous edifice porosity may arise over time. Volcán Rincón de la Vieja, for example, exhibits contrasting flank compositions as tephra is predominantly deposited on the western side due to the prevailing trade winds, whereas dense lava flows have been historically concentrated to the north and south (Kempter et al, 1996).…”

Section: Implications For Volcanologymentioning

confidence: 99%

“…Sparks, 1978). If the permeability of a volcanic system (including the edifice) is high, volatiles may escape from the magma and the propensity for explosive behaviour may be reduced; conversely, low system permeability could promote pressure build-up and violent eruptive activity, a concept underlying numerous studies in volcanology (for example Eichelberger et al, 1986;Woods and Koyaguchi, 1994;Rust et al, 2004;Edmonds and Herd, 2007;Mueller et al, 2008Mueller et al, , 2011Nguyen et al, 2014;Okumura and Sasaki, 2014;Gaunt et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

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Inelastic compaction and permeability evolution in volcanic rock

2017

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Abstract. Active volcanoes are mechanically dynamic environments, and edifice-forming material may often be subjected to significant amounts of stress and strain. It is understood that porous volcanic rock can compact inelastically under a wide range of in situ conditions. In this contribution, we explore the evolution of porosity and permeability -critical properties influencing the style and magnitude of volcanic activity -as a function of inelastic compaction of porous andesite under triaxial conditions. Progressive axial strain accumulation is associated with progressive porosity loss. The efficiency of compaction was found to be related to the effective confining pressure under which deformation occurred: at higher effective pressure, more porosity was lost for any given amount of axial strain. Permeability evolution is more complex, with small amounts of stress-induced compaction ( < 0.05, i.e. less than 5 % reduction in sample length) yielding an increase in permeability under all effective pressures tested, occasionally by almost 1 order of magnitude. This phenomenon is considered here to be the result of improved connectivity of formerly isolated porosity during triaxial loading. This effect is then overshadowed by a decrease in permeability with further inelastic strain accumulation, especially notable at high axial strains (> 0.20) where samples may undergo a reduction in permeability by 2 orders of magnitude relative to their initial values. A physical limit to compaction is discussed, which we suggest is echoed in a limit to the potential for permeability reduction in compacting volcanic rock. Compiled literature data illustrate that at high axial strain (both in the brittle and ductile regimes), porosity φ and permeability k tend to converge towards intermediate values (i.e. 0.10 ≤ φ ≤ 0.20; 10 −14 ≤ k ≤10 −13 m 2 ). These results are discussed in light of their potential ramifications for impacting edifice outgassing -and in turn, eruptive activity -in active volcanoes.

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The porosity of pyroclasts as an indicator of volcanic explosivity

Cited by 60 publications

References 21 publications

Matrix permeability of reservoir rocks, Ngatamariki geothermal field, Taupo Volcanic Zone, New Zealand

Matrix permeability of reservoir rocks, Ngatamariki geothermal field, Taupo Volcanic Zone, New Zealand

Textural Insights Into the Evolving Lava Dome Cycles at Santiaguito Lava Dome, Guatemala

Inelastic compaction and permeability evolution in volcanic rock

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