A general model for welding of ash particles in volcanic systems validated using in situ X-ray tomography

Fabian B. Wadsworth; Jérémie Vasseur; Jenny Schauroth; Edward W. Llewellin; Katherine J. Dobson; Tegan Havard; Bettina Scheu; Felix W. von Aulock; James E. Gardner; Donald B. Dingwell; Kai Uwe Hess; Mathieu Colombier; Federica Marone; Hugh Tuffen; Michael J. Heap

doi:10.1016/j.epsl.2019.115726

A general model for welding of ash particles in volcanic systems validated using in situ X-ray tomography

Fabian B. Wadsworth^*, Jérémie Vasseur, Jenny Schauroth, Edward W. Llewellin, Katherine J. Dobson, Tegan Havard, Bettina Scheu, Felix W. von Aulock, James E. Gardner, Donald B. Dingwell, Kai Uwe Hess, Mathieu Colombier, Federica Marone, Hugh Tuffen, Michael J. Heap

^*Corresponding author for this work

Civil And Environmental Engineering

Research output: Contribution to journal › Article › peer-review

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Abstract

Welding occurs during transport and deposition of volcanic particles in diverse settings, including pyroclastic density currents, volcanic conduits, and jet engines. Welding rate influences hazard-relevant processes, and is sensitive to water concentration in the melt. We characterize welding of fragments of crystal-free, water-supersaturated rhyolitic glass at high temperature using in-situ synchrotron-source X-ray tomography. Continuous measurement of evolving porosity and pore-space geometry reveals that porosity decays to a percolation threshold of 1–3 vol.%, at which bubbles become isolated and welding ceases. We develop a new mathematical model for this process that combines sintering and water diffusion, which fits experimental data without requiring empirically-adjusted parameters. A key advance is that the model is valid for systems in which welding is driven by confining pressure, surface tension, or a combination of the two. We use the model to constrain welding timescales in a wide range of volcanic settings. We find that volcanic systems span the regime divide between capillary welding in which surface tension is important, and pressure welding in which confining pressure is important. Our model predicts that welding timescales in nature span seconds to years and that this is dominantly dependent on the particle viscosity or the evolution of this viscosity during particle degassing. We provide user-friendly tools, written in Python™ and in Excel®, to solve for the evolution of porosity and dissolved water concentration during welding for user-defined initial conditions.

Original language	English
Article number	115726
Number of pages	9
Journal	Earth and Planetary Science Letters
Volume	525
Early online date	19 Aug 2019
DOIs	https://doi.org/10.1016/j.epsl.2019.115726
Publication status	Published - 1 Nov 2019

Funding

We acknowledge European Research Council Advanced Grant EVOKES 247076 , UK National Environment Research Council ( NERC ) grants No. NE/N002954/1 and No. NE/M018687/1 , a fellowship from the Institute of Advanced Study at Durham University (to J. Gardner) and from the Centre for Advanced Study at the Ludwig-Maximilians-Universität ( LMU ) in Munich (to F. Wadsworth), a Royal Society University Research Fellowship (to H. Tuffen) and Royal Society International Exchange grant (to H. Tuffen and M. Heap), DFG through the projects SCHE 1634/1-1 and Di 431/33-1 , and the VUELCO consortium funded under the EU's FP7 grant agreement 282759 . The Paul-Scherer-Institute (Swiss Light Source) awarded beamtime under proposals No. 20141231 and No. 20150413 at the TOMCAT beamline. Thanks to Yan Lavallée and Jackie Kendrick for valuable discussions and for supporting J. Schauroth's contribution to this work. S. Wiesmaier is thanked for assistance on the beamline. All raw data are available on request from the authors. Codes available via VHub at https://vhub.org/resources/4568 . We thank Tamsin Mather for editorial handling, and Stephan Kolzenburg and an anonymous reviewer for constructive comments.

Keywords

jet engine
obsidian
porosity
sintering
surface tension
tuffisite

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Wadsworth-etal-EPSL-2019-A-general-model-for-welding-of-ash-particles-in-volcanicAccepted author manuscript, 1.38 MBLicence: CC BY-NC-ND 4.0

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Cite this

Wadsworth, F. B., Vasseur, J., Schauroth, J., Llewellin, E. W., Dobson, K. J., Havard, T., Scheu, B., von Aulock, F. W., Gardner, J. E., Dingwell, D. B., Hess, K. U., Colombier, M., Marone, F., Tuffen, H., & Heap, M. J. (2019). A general model for welding of ash particles in volcanic systems validated using in situ X-ray tomography. Earth and Planetary Science Letters, 525, Article 115726. https://doi.org/10.1016/j.epsl.2019.115726

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title = "A general model for welding of ash particles in volcanic systems validated using in situ X-ray tomography",

abstract = "Welding occurs during transport and deposition of volcanic particles in diverse settings, including pyroclastic density currents, volcanic conduits, and jet engines. Welding rate influences hazard-relevant processes, and is sensitive to water concentration in the melt. We characterize welding of fragments of crystal-free, water-supersaturated rhyolitic glass at high temperature using in-situ synchrotron-source X-ray tomography. Continuous measurement of evolving porosity and pore-space geometry reveals that porosity decays to a percolation threshold of 1–3 vol.%, at which bubbles become isolated and welding ceases. We develop a new mathematical model for this process that combines sintering and water diffusion, which fits experimental data without requiring empirically-adjusted parameters. A key advance is that the model is valid for systems in which welding is driven by confining pressure, surface tension, or a combination of the two. We use the model to constrain welding timescales in a wide range of volcanic settings. We find that volcanic systems span the regime divide between capillary welding in which surface tension is important, and pressure welding in which confining pressure is important. Our model predicts that welding timescales in nature span seconds to years and that this is dominantly dependent on the particle viscosity or the evolution of this viscosity during particle degassing. We provide user-friendly tools, written in Python{\texttrademark} and in Excel{\textregistered}, to solve for the evolution of porosity and dissolved water concentration during welding for user-defined initial conditions.",

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author = "Wadsworth, {Fabian B.} and J{\'e}r{\'e}mie Vasseur and Jenny Schauroth and Llewellin, {Edward W.} and Dobson, {Katherine J.} and Tegan Havard and Bettina Scheu and {von Aulock}, {Felix W.} and Gardner, {James E.} and Dingwell, {Donald B.} and Hess, {Kai Uwe} and Mathieu Colombier and Federica Marone and Hugh Tuffen and Heap, {Michael J.}",

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Wadsworth, FB, Vasseur, J, Schauroth, J, Llewellin, EW, Dobson, KJ, Havard, T, Scheu, B, von Aulock, FW, Gardner, JE, Dingwell, DB, Hess, KU, Colombier, M, Marone, F, Tuffen, H & Heap, MJ 2019, 'A general model for welding of ash particles in volcanic systems validated using in situ X-ray tomography', Earth and Planetary Science Letters, vol. 525, 115726. https://doi.org/10.1016/j.epsl.2019.115726

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AU - Wadsworth, Fabian B.

AU - Vasseur, Jérémie

AU - Schauroth, Jenny

AU - Llewellin, Edward W.

AU - Dobson, Katherine J.

AU - Havard, Tegan

AU - Scheu, Bettina

AU - von Aulock, Felix W.

AU - Gardner, James E.

AU - Dingwell, Donald B.

AU - Hess, Kai Uwe

AU - Colombier, Mathieu

AU - Marone, Federica

AU - Tuffen, Hugh

AU - Heap, Michael J.

PY - 2019/11/1

Y1 - 2019/11/1

N2 - Welding occurs during transport and deposition of volcanic particles in diverse settings, including pyroclastic density currents, volcanic conduits, and jet engines. Welding rate influences hazard-relevant processes, and is sensitive to water concentration in the melt. We characterize welding of fragments of crystal-free, water-supersaturated rhyolitic glass at high temperature using in-situ synchrotron-source X-ray tomography. Continuous measurement of evolving porosity and pore-space geometry reveals that porosity decays to a percolation threshold of 1–3 vol.%, at which bubbles become isolated and welding ceases. We develop a new mathematical model for this process that combines sintering and water diffusion, which fits experimental data without requiring empirically-adjusted parameters. A key advance is that the model is valid for systems in which welding is driven by confining pressure, surface tension, or a combination of the two. We use the model to constrain welding timescales in a wide range of volcanic settings. We find that volcanic systems span the regime divide between capillary welding in which surface tension is important, and pressure welding in which confining pressure is important. Our model predicts that welding timescales in nature span seconds to years and that this is dominantly dependent on the particle viscosity or the evolution of this viscosity during particle degassing. We provide user-friendly tools, written in Python™ and in Excel®, to solve for the evolution of porosity and dissolved water concentration during welding for user-defined initial conditions.

AB - Welding occurs during transport and deposition of volcanic particles in diverse settings, including pyroclastic density currents, volcanic conduits, and jet engines. Welding rate influences hazard-relevant processes, and is sensitive to water concentration in the melt. We characterize welding of fragments of crystal-free, water-supersaturated rhyolitic glass at high temperature using in-situ synchrotron-source X-ray tomography. Continuous measurement of evolving porosity and pore-space geometry reveals that porosity decays to a percolation threshold of 1–3 vol.%, at which bubbles become isolated and welding ceases. We develop a new mathematical model for this process that combines sintering and water diffusion, which fits experimental data without requiring empirically-adjusted parameters. A key advance is that the model is valid for systems in which welding is driven by confining pressure, surface tension, or a combination of the two. We use the model to constrain welding timescales in a wide range of volcanic settings. We find that volcanic systems span the regime divide between capillary welding in which surface tension is important, and pressure welding in which confining pressure is important. Our model predicts that welding timescales in nature span seconds to years and that this is dominantly dependent on the particle viscosity or the evolution of this viscosity during particle degassing. We provide user-friendly tools, written in Python™ and in Excel®, to solve for the evolution of porosity and dissolved water concentration during welding for user-defined initial conditions.

KW - jet engine

KW - obsidian

KW - porosity

KW - sintering

KW - surface tension

KW - tuffisite

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VL - 525

JO - Earth and Planetary Science Letters

JF - Earth and Planetary Science Letters

M1 - 115726

ER -

A general model for welding of ash particles in volcanic systems validated using in situ X-ray tomography

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Kate Dobson

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A general model for welding of ash particles in volcanic systems validated using in situ X-ray tomography

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Kate Dobson

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