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

Wadsworth, F.B. and Vasseur, J. and Schauroth, J. and Llewellin, E.W. and Dobson, K.J. and Havard, T. and Scheu, B. and von Aulock, F.W. and Gardner, J.E. and Dingwell, D.B. and Hess, K.-U. and Colombier, M. and Marone, F. and Tuffen, H. and 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: 115726. ISSN 0012-821X

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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.

Item Type:

Journal Article

Journal or Publication Title:

Earth and Planetary Science Letters

Additional Information:

This is the author’s version of a work that was accepted for publication in Earth and Planetary Science Letters. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Earth and Planetary Science Letters, 525, 2019 DOI: 10.1016/j.epsl.2019.115726

Uncontrolled Keywords:

/dk/atira/pure/subjectarea/asjc/1900/1901

Subjects:

?? sinteringporositysurface tensiontuffisitejet engineobsidianearth and planetary sciences (miscellaneous)geochemistry and petrologygeophysicsspace and planetary science ??

Departments:

Faculty of Science and Technology > Lancaster Environment Centre

ID Code:

136407

Deposited By:

ep_importer_pure

Deposited On:

04 Sep 2019 09:20

Refereed?:

Yes

Published?:

Published