Pathways for degassing during the lava dome eruption of Mount St. Helens 2004–2008

Gaunt, Elizabeth; Sammonds, Peter; Meredith, P. G.; Smith, Rosanna; Pallister, John S.

doi:10.1130/g35940.1

Cited by 75 publications

(54 citation statements)

References 28 publications

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“…We showed that in highly crystalline magmas, fracture networks control not only the magnitude but also the location and direction of fluid movement (Gaunt et al 2014). We found that permeability was highly anisotropic in the shear fractured rocks at conduit margins, but broadly isotropic in the column interior.…”

Section: Introductionmentioning

confidence: 79%

“…1). Water permeability measurements made at room temperature and an effective pressure of 10 MPa also show that permeability is independent of sample orientation (Gaunt et al 2014), indicating that the fluid transport properties of this lava dome block are also broadly isotropic.…”

Section: Acoustic Wave Velocitiesmentioning

confidence: 84%

“…Microfractures may form the dominant porosity in dense, degassed magma that forms lava spines such as those seen at Mount St. Helens (MSH) (Scott et al 2008;Pallister et al 2013) or volcanic plug rocks that often form before vulcanian events such as those seen at Tungurahua (Hall et al 1999); microfractures dominate the microstructure (Pallister et al 2013). Under these conditions, fluid movement through the crystallizing magma depends more on the development of the permeable fracture network and less on the expansion and coalescence of bubbles (Gaunt et al 2014). There are multiple factors that influence the magnitude and direction of fluid movement (e.g., Gaunt et al 2014;Lavallee et al 2013;Nara et al 2010).…”

Section: Introductionmentioning

confidence: 99%

“…Under these conditions, fluid movement through the crystallizing magma depends more on the development of the permeable fracture network and less on the expansion and coalescence of bubbles (Gaunt et al 2014). There are multiple factors that influence the magnitude and direction of fluid movement (e.g., Gaunt et al 2014;Lavallee et al 2013;Nara et al 2010). Temperature is one such factor, Editorial responsibility: K.V.…”

Section: Introductionmentioning

confidence: 99%

“…Experiments were conducted at conditions appropriate for the upper volcanic conduit and lava dome (confining pressure of 10 MPa, temperatures ≤900°C and fluid pressures of 5 MPa). For this study, we examine microfracture development within undeformed dome rocks from the conduit interior (Gaunt et al 2014) to understand the influence of magma temperature on gas movement through microfracture networks. We combine dilatometry and thermal stressing tests with measurements of acoustic emission (AE) and elastic wave velocities to evaluate the damage caused by cycles of heating and cooling.…”

Section: Introductionmentioning

confidence: 99%

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Effect of temperature on the permeability of lava dome rocks from the 2004–2008 eruption of Mount St. Helens

et al. 2016

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As magma ascends to shallow levels in the volcanic conduit, volatile exsolution can produce a dramatic increase in the crystal content of the magma. During extrusion, low porosity, highly crystalline magmas are subjected to thermal stresses which generate permeable microfracture networks. How these networks evolve and respond to changing temperature has significant implications for gas escape and hence volcano explosivity. Here, we report the first laboratory experimental study on the effect of temperature on the permeability of lava dome rocks under environmental conditions designed to simulate the shallow volcanic conduit and lava dome. Samples were collected for this study from the 2004-2008 lava dome eruption of Mount St. Helens (Washington State, USA). We show that the evolution of microfracture networks, and their permeability, depends strongly on temperature changes. Our results show that permeability decreases by nearly four orders of magnitude as temperature increases from room temperature to 800°C. Above 800°C, the rock samples become effectively impermeable. Repeated cycles of heating leads to sample compaction and a reduction in fracture density and therefore a decrease in permeability. We argue that changes in eruption regimes from effusive to explosive activity can be explained by strongly decreasing permeability caused by repeated heating of magma, conduit walls and volcanic plugs or domes. Conversely, magma becomes more permeable as it cools, which will reduce explosivity.

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Section: Introductionmentioning

confidence: 79%

Section: Acoustic Wave Velocitiesmentioning

confidence: 84%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Effect of temperature on the permeability of lava dome rocks from the 2004–2008 eruption of Mount St. Helens

et al. 2016

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Permeability of compacting porous lavas

et al. 2015

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The highly transient nature of outgassing commonly observed at volcanoes is in part controlled by the permeability of lava domes and shallow conduits. Lava domes generally consist of a porous outer carapace surrounding a denser lava core with internal shear zones of variable porosity. Here we examine densification using uniaxial compression experiments on variably crystalline and porous rhyolitic dome lavas from the Taupo Volcanic Zone. Experiments were conducted at 900°C and an applied stress of 3 MPa to 60% strain, while monitoring acoustic emissions to track cracking. The evolution of the porous network was assessed via X-ray computed tomography, He-pycnometry, and relative gas permeability. High starting connected porosities led to low apparent viscosities and high strain rates, initially accompanied by abundant acoustic emissions. As compaction ensued, the lavas evolved; apparent viscosity increased and strain rate decreased due to strain hardening of the suspensions. Permeability fluctuations resulted from the interplay between viscous flow and brittle failure. Where phenocrysts were abundant, cracks had limited spatial extent, and pore closure decreased axial and radial permeability proportionally, maintaining the initial anisotropy. In crystal-poor lavas, axial cracks had a more profound effect, and permeability anisotropy switched to favor axial flow. Irrespective of porosity, both crystalline samples compacted to a threshold minimum porosity of 17-19%, whereas the crystal-poor sample did not achieve its compaction limit. This indicates that unconfined loading of porous dome lavas does not necessarily form an impermeable plug and may be hindered, in part by the presence of crystals.

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Strain‐induced permeability increase in volcanic rock

Farquharson

Heap

Baud

2016

Geophysical Research Letters

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The extrusion of dense, viscous magma typically occurs along pronounced conduit‐parallel faults. To better understand the evolution of fault permeability with increasing strain, we measured the permeability of low‐porosity volcanic rock samples (basalt and andesite) that were deformed in the brittle regime to various levels of inelastic strain. We observed a progressive increase in sample permeability with increasing inelastic strain (i.e., with continued sliding on the fault plane). At the maximum imposed inelastic strain (0.11), sample permeability had increased by 3 orders of magnitude or more for all sample sets. Microstructural observations show that narrow shear fractures evolve into more complex fracture systems characterized by thick zones of friction‐induced cataclasis (gouge) with increasing inelastic strain. These data suggest that the permeability of conduit‐parallel faults hosted in the rock at the conduit‐wall rock interface will increase during lava extrusion, thus facilitating outgassing and hindering the transition to explosive behavior.

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Pathways for degassing during the lava dome eruption of Mount St. Helens 2004–2008

Cited by 75 publications

References 28 publications

Effect of temperature on the permeability of lava dome rocks from the 2004–2008 eruption of Mount St. Helens

Effect of temperature on the permeability of lava dome rocks from the 2004–2008 eruption of Mount St. Helens

Permeability of compacting porous lavas

Strain‐induced permeability increase in volcanic rock

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