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Submarine giant pumice: a window into the shallow conduit dynamics of a recent silicic eruption

Mitchell, SJ, Houghton, BF, Carey, RJ ORCID: 0000-0003-2015-6419, Manga, M, Fauria, KE, Jones, MR, Soule, SA, Conway, CE, Wei, Z and Giachetti, T 2019 , 'Submarine giant pumice: a window into the shallow conduit dynamics of a recent silicic eruption' , Bulletin of Volcanology , pp. 1-22 , doi: 10.1007/s00445-019-1298-5.

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Abstract

Meter-scale vesicular blocks, termed “giant pumice,” are characteristic primary products of many subaqueous silicic eruptions. The size of giant pumices allows us to describemeter-scale variations in textures and geochemistrywith implications for shearing processes, ascent dynamics, and thermal histories within submarine conduits prior to eruption. The submarine eruption of Havre volcano, Kermadec Arc, in 2012, produced at least 0.1 km3 of rhyolitic giant pumice from a single 900-m-deep vent, with blocks up to 10 m in size transported to at least 6 km from source. We sampled and analyzed 29 giant pumices from the 2012 Havre eruption. Geochemical analyses of whole rock and matrix glass show no evidence for geochemical heterogeneities in parental magma; any textural variations can be attributed to crystallization of phenocrysts andmicrolites, and degassing. Extensive growth of microlites occurred near conduit walls where magma was then mingled with ascending microlite-poor, low viscosity rhyolite. Meter- to micron-scale textural analyses of giant pumices identify diversity throughout an individual block and between the exteriors of individual blocks.We identify evidence for post-disruption vesicle growth during pumice ascent in the water column above the submarine vent. A 2D cumulative strain model with a flared, shallow conduit may explain observed vesicularity contrasts (elongate tube vesicles vs spherical vesicles). Low vesicle number densities in these pumices from this high-intensity silicic eruption demonstrate the effect of hydrostatic pressure above a deep submarine vent in suppressing rapid late-stage bubble nucleation and inhibiting explosive fragmentation in the shallow conduit.

Item Type: Article
Authors/Creators:Mitchell, SJ and Houghton, BF and Carey, RJ and Manga, M and Fauria, KE and Jones, MR and Soule, SA and Conway, CE and Wei, Z and Giachetti, T
Keywords: giant pumice, submarine volcanism, banding, tube pumice, bubble deformation, conduit dynamics, submarine eruption, volcano, marine
Journal or Publication Title: Bulletin of Volcanology
Publisher: Springer-Verlag
ISSN: 0258-8900
DOI / ID Number: 10.1007/s00445-019-1298-5
Copyright Information:

Copyright 2019 The Authors

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