Permeability and porosity relationships of edifice-forming andesites: A combined field and laboratory study

Farquharson, Jamie; Heap, Michael; Varley, Nick; Baud, Patrick; Reuschlé, Thierry

doi:10.1016/j.jvolgeores.2015.03.016

Cited by 159 publications

(131 citation statements)

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“…Alteration has been previously shown to weaken volcanic rocks (Pola et al 2014;Wyering et al 2014;Heap et al 2015b). Permeability measurements show that permeability increases as porosity increases, in accordance with other measurements on basaltic andesites and andesites (Farquharson et al 2015;Kushnir et al 2016;Heap and Kennedy 2016).…”

Section: Discussionsupporting

confidence: 89%

Flank instability assessment at Kick-’em-Jenny submarine volcano (Grenada, Lesser Antilles): a multidisciplinary approach using experiments and modeling

et al. 2016

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Kick-'em-Jenny (KeJ)-located ca. 8 km north of the island of Grenada-is the only active submarine volcano of the Lesser Antilles Volcanic Arc. Previous investigations of KeJ revealed that it lies within a collapse scar inherited from a past flank instability episode. To assess the likelihood of future collapse, we employ here a combined laboratory and modeling approach. Lavas collected using a remotely operated vehicle (ROV) provided samples to perform the first rock physical property measurements for the materials comprising the KeJ edifice. Uniaxial and triaxial deformation experiments showed that the dominant failure mode within the edifice host rock is brittle. Edifice fractures (such as those at Champagne Vent) will therefore assist the outgassing of the nearby magma-filled conduit, favoring effusive behavior. These laboratory data were then used as input parameters in models of slope stability. First, relative slope stability analysis revealed that the SW to N sector of the volcano displays a deficit of mass/volume with respect to a volcanoid (ideal 3D surface). Slope stability analysis using a limit equilibrium method (LEM) showed that KeJ is currently stable, since all values of stability factor or factor of safety (Fs) are greater than unity.The lowest values of Fs were found for the SW-NW sector of the volcano (the sector displaying a mass/volume deficit). Although currently stable, KeJ may become unstable in the future. Instability (severe reductions in Fs) could result, for example, from overpressurization due to the growth of a cryptodome. Our modeling has shown that instabilityinduced flank collapse will most likely initiate from the SW-NW sector of KeJ, therefore mobilizing a volume of at least ca. 0.7 km 3 . The mobilization of ca. 0.7 km 3 of material is certainly capable of generating a tsunami that poses a significant hazard to the southern islands of the West Indies.

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Section: Discussionsupporting

confidence: 89%

Flank instability assessment at Kick-’em-Jenny submarine volcano (Grenada, Lesser Antilles): a multidisciplinary approach using experiments and modeling

et al. 2016

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“…It is interesting that aspect ratio and roundness do not provide a good fit, which suggests that embayments along the pore perimeter do not contribute to fluid flow. This is analogous to the low permeability of some samples with micro-porosity characterised by high surface area in Farquharson et al (2015), where many micropores did not contribute to fluid flow. We also attempted to determine if a correlation between increased microfracture density and increased connected porosity was present, as has been observed in reservoir rocks of the nearby Rotokawa Andesite .…”

Section: Microfracture and Pore Analysismentioning

confidence: 61%

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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“…The host rock porosity-permeability is bracketed by other porosity-permeability measurements on lavas from Volcán de Colima (Kendrick et al, 2013;Farquharson et al, 2015), and is akin to measurements on other lavas from basaltic (Schaefer et al, 2015) to dacitic (Mueller et al, 2005) to rhyolitic (Heap et al, 2014a;Okumura and Sasaki, 2014). The trend in porosity-permeability data is well described by the relationship given for effusive lavas in Mueller et al (2005), as is the majority of the natural tuffisite, with some examples falling into a range that is slightly more permeable than anticipated from their porosity (Figure 7).…”

Section: Discussionmentioning

confidence: 99%

“…On the right, this porosity and permeability relationship for the eight samples of both the natural host rock and tuffisite veins are compared to the crushed dome material and sintered tuffisite analogs from 940 to 980 • C (data in Table 3). This is compared to porosity-permeability measurements on other lavas from Volcán de Colima (Kendrick et al, 2013;Farquharson et al, 2015) and to lavas from elsewhere ranging from basalt (Pacaya; Schaefer et al, 2015) to dacite (Mount Unzen; Mueller et al, 2005) rhyolite (Mount Meagre; Heap et al, 2014a) and in addition it is compared to the results of compaction experiments on chips of rhyolite lava (Okumura and Sasaki, 2014) and overlain by the porosity-permeability relationship for effusive lava given by Mueller et al (2005). The plot shows the region in which the neck-formation regime is active, i.e., the region in which sintering materials plot, but where they do not follow the anticipated porosity-permeability trend for lavas.…”

Section: Discussionmentioning

confidence: 99%

Blowing Off Steam: Tuffisite Formation As a Regulator for Lava Dome Eruptions

et al. 2016

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Tuffisites are veins of variably sintered, pyroclastic particles that form in conduits and lava domes as a result of localized fragmentation events during gas-and-ash explosions. Those observed in-situ on the active 2012 lava dome of Volcán de Colima range from voids with intra-clasts showing little movement and interpreted to be failure-nuclei, to sub-parallel lenses of sintered granular aggregate interpreted as fragmentation horizons, through to infilled fractures with evidence of viscous remobilization. All tuffisites show evidence of sintering. Further examination of the complex fracture-and-channel patterns reveals viscous backfill by surrounding magma, suggesting that lava fragmentation was followed by stress relaxation and continued viscous deformation as the tuffisites formed. The natural tuffisites are more permeable than the host andesite, and have a wide range of porosity and permeability compared to a narrower window for the host rock, and gaging from their significant distribution across the dome, we posit that the tuffisite veins may act as important outgassing pathways. To investigate tuffisite formation we crushed and sieved andesite from the lava dome and sintered it at magmatic temperatures for different times. We then assessed the healing and sealing ability by measuring porosity and permeability, showing that sintering reduces both over time. During sintering the porosity-permeability reduction occurs due to the formation of viscous necks between adjacent grains, a process described by the neck-formation model of Frenkel (1945). This process leads the granular starting material to a porosity-permeability regime anticipated for effusive lavas, and which describes the natural host lava as well as the most impervious of natural tuffisites. This suggests that tuffisite formation at Volcán de Colima constructed a permeable network that enabled gas to bleed passively from the magma. We postulate that this progressively reduced the lava dome's ability to seal and build pressure that drives explosions. Indeed, the time interval between explosions during 2007-2011 gradually increased before the onset of a period of quiescence starting in June 2011. We suggest that the permeability evolution during tuffisite formation has important consequences for modeling of gas-and-ash explosions, common at dome-forming volcanoes.

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Permeability and porosity relationships of edifice-forming andesites: A combined field and laboratory study

Cited by 159 publications

References 73 publications

Flank instability assessment at Kick-’em-Jenny submarine volcano (Grenada, Lesser Antilles): a multidisciplinary approach using experiments and modeling

Flank instability assessment at Kick-’em-Jenny submarine volcano (Grenada, Lesser Antilles): a multidisciplinary approach using experiments and modeling

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

Blowing Off Steam: Tuffisite Formation As a Regulator for Lava Dome Eruptions

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