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 |
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Article number | 115726 |
Number of pages | 9 |
Journal | Earth and Planetary Science Letters |
Volume | 525 |
Early online date | 19 Aug 2019 |
DOIs | |
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