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A reappraisal of explosive–effusive silicic eruption dynamics: syn-eruptive assembly of lava from the products of cryptic fragmentation

Wadsworth, Fabian B.; Llewellin, Edward W.; Castro, Jonathan M.; Tuffen, Hugh; Schipper, C. Ian; Gardner, James E.; Vasseur, Jérémie; Foster, Annabelle; Damby, David E.; McIntosh, Iona M.; Boettcher, Sina; Unwin, Holly E.; Heap, Michael J.; Farquharson, Jamie I.; Dingwell, Donald B.; Iacovino, Kayla; Paisley, Rebecca; Jones, Calvin; Whattam, Jack

A reappraisal of explosive–effusive silicic eruption dynamics: syn-eruptive assembly of lava from the products of cryptic fragmentation Thumbnail


Authors

Jonathan M. Castro

Hugh Tuffen

C. Ian Schipper

James E. Gardner

Jérémie Vasseur

David E. Damby

Iona M. McIntosh

Sina Boettcher

Holly E. Unwin

Michael J. Heap

Jamie I. Farquharson

Donald B. Dingwell

Kayla Iacovino

Rebecca Paisley

Calvin Jones

Jack Whattam



Abstract

Silicic volcanic eruptions range in style from gently effusive to highly explosive, and may switch style unpredictably during a single eruption. Direct observations of subaerial rhyolitic eruptions (Chaiten 2008, Cordón Caulle 2011–2012, Chile) challenged long-standing paradigms of explosive and effusive eruptive styles and led to the formulation of new models of hybrid activity. However, the processes that govern such hybrid explosive–effusive activity remain poorly understood. Here, we bring together observations of the well-studied 2011–2012 Cordón Caulle eruption with new textural and petrologic data on erupted products, and video and still imagery of the eruption. We infer that all of the activity – explosive, effusive, and hybrid – was fed by explosive fragmentation at depth, and that effusive behaviour arose from sticking and sintering, in the shallow vent region, of the clastic products of deeper, cryptic fragmentation. We use a scaling approach to determine that there is sufficient time available, during emplacement, for diffusive pyroclast degassing and sintering to produce a degassed plug that occludes the shallow conduit, feeding clastogenic, apparently effusive, lava-like deposits. Based on evidence from Cordón Caulle, and from other similar eruptions, we further argue that hybrid explosive–effusive activity is driven by episodic gas-fracking of the occluding lava plug, fed by the underlying pressurized ash- and pyroclast-laden region. The presence of a pressurized pocket of ash-laden gas within the conduit provides a mechanism for generation of harmonic tremor, and for syn-eruptive laccolith intrusion, both of which were features of the Cordón Caulle eruption. We conclude that the cryptic fragmentation models is more consistent with available evidence than the prevailing model for effusion of silicic lava that assume coherent non-fragmental rise of magma from depth to the surface without wholesale explosive fragmentation.

Citation

Wadsworth, F. B., Llewellin, E. W., Castro, J. M., Tuffen, H., Schipper, C. I., Gardner, J. E., …Whattam, J. (2022). A reappraisal of explosive–effusive silicic eruption dynamics: syn-eruptive assembly of lava from the products of cryptic fragmentation. Journal of Volcanology and Geothermal Research, 432, https://doi.org/10.1016/j.jvolgeores.2022.107672

Journal Article Type Article
Acceptance Date Sep 12, 2022
Online Publication Date Nov 24, 2022
Publication Date 2022-12
Deposit Date Dec 22, 2022
Publicly Available Date Dec 22, 2022
Journal Journal of Volcanology and Geothermal Research
Print ISSN 0377-0273
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 432
DOI https://doi.org/10.1016/j.jvolgeores.2022.107672

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