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  • Schipper et al 2021 Accepted Version

    Rights statement: The final publication is available at Springer via http://dx.doi.org/10.1007/s00445-020-01432-1

    Accepted author manuscript, 2.61 MB, PDF document

    Available under license: CC BY-NC: Creative Commons Attribution-NonCommercial 4.0 International License

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Silicic conduits as supersized tuffisites: Clastogenic influences on shifting eruption styles at Cordón Caulle volcano (Chile)

Research output: Contribution to journalJournal articlepeer-review

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  • C.I. Schipper
  • J.M. Castro
  • B.M. Kennedy
  • H. Tuffen
  • J. Whattam
  • F.B. Wadsworth
  • R. Paisley
  • R.H. Fitzgerald
  • E. Rhodes
  • L.N. Schaefer
  • P.A. Ashwell
  • P. Forte
  • G. Seropian
  • B.V. Alloway
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Article number11
<mark>Journal publication date</mark>27/01/2021
<mark>Journal</mark>Bulletin of Volcanology
Issue number2
Volume83
Number of pages22
Publication StatusPublished
<mark>Original language</mark>English

Abstract

Understanding the processes that drive explosive-effusive transitions during large silicic eruptions is crucial to hazard mitigation. Conduit models usually treat magma ascent and degassing as a gradual, unidirectional progression from bubble nucleation through magmatic fragmentation. However, there is growing evidence for the importance of bi-directional clastogenic processes that sinter fragmented materials into coherent clastogenic magmas. Bombs that were ejected immediately before the first emergence of lava in the 2011–2012 eruption at Cordón Caulle volcano (Chile) are texturally heterogeneous composite assemblages of welded pyroclastic material. Although diverse in density and appearance, SEM and X-ray tomographic analysis show them all to have been formed by multi-generational viscous sintering of fine ash. Sintering created discrete clasts ranging from obsidian to pumice and formed a pervasive clast-supporting matrix that assembled these clasts into a conduit-sealing plug. An evaluation of sintering timescales reveals texturally disparate bomb components to represent only minutes of difference in residence time within the conduit. Permeability modelling indicates that the plug was an effective conduit seal, with outgassing potential—even from high-porosity regions—being limited by the inability of gas to flow across tendrils of densely sintered inter-clast matrix. Contrary to traditional perspectives, declining expressions of explosivity at the surface need not be preceded or accompanied by a decline in fragmentation efficiency. Instead, they result from tips in balance between the opposing processes of fragmentation and sintering that occur in countless cycles within volcanic conduits. These processes may be particularly enhanced at silicic fissure volcanoes, which have laterally extensive subsurface plumbing systems that require complex magma ascent pathways. The textures investigated here reveal the processes occurring within silicic fissures to be phenomenologically identical to those that have been inferred to occur in tuffisite veins: silicic conduits are essentially supersized examples of edifice-penetrating tuffisites. 

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The final publication is available at Springer via http://dx.doi.org/10.1007/s00445-020-01432-1