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

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A Correction to this article was published on 19 February 2021

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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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Funding

CIS acknowledges support from a Faculty Strategic Research Grant from VUW. BMK, RHF, ER, LNS and GS were supported by the Royal Society Te Apārangi Marsden project ‘Shaking magma to trigger volcanic eruptions’. RHF was additionally supported by a Ngāi Tahu Research Centre Doctoral Scholarship, Te Punenga Grant and Mason Trust Grant. RP was supported by travel and research grants from McGill University. HT was supported by Royal Society University Research Fellowship UF140716. Access to the Australian Synchrotron was granted by ANSTO (M7045, M9095, M11725) and the New Zealand Synchrotron Group. The authors thank M. Pistolesi, an anonymous reviewer, and handling editor K.V. Cashman for constructive comments that helped to improve this work.

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Correspondence to C. Ian Schipper.

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Editorial responsibility: K.V. Cashman

The original online version of this article was revised: The presentation of Table 1 was incorrect.

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Schipper, C.I., Castro, J.M., Kennedy, B.M. et al. Silicic conduits as supersized tuffisites: Clastogenic influences on shifting eruption styles at Cordón Caulle volcano (Chile). Bull Volcanol 83, 11 (2021). https://doi.org/10.1007/s00445-020-01432-1

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  • DOI: https://doi.org/10.1007/s00445-020-01432-1

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