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Contrasting pyroclast density spectra from subaerial and submarine silicic eruptions in the Kermadec arc: implications for eruption processes and dredge sampling

Record type: Article

Pyroclastic deposits from four caldera volcanoes in the Kermadec arc have been sampled from subaerial sections (Raoul and Macauley) and by dredging from the submerged volcano flanks (Macauley, Healy, and the newly discovered Raoul SW). Suites of 16–32 mm sized clasts have been analyzed for density and shape, and larger clasts have been analyzed for major element compositions. Density spectra for subaerial dry-type eruptions on Raoul Island have narrow unimodal distributions peaking at vesicularities of 80–85%, whereas ingress of external water (wet-type eruption) or extended timescales for degassing generate broader distributions, including denser clasts. Submarine-erupted pyroclasts show two different patterns. Healy and Raoul SW dredge samples and Macauley Island subaerial-emplaced samples are dominated by modes at ~80–85%, implying that submarine explosive volcanism at high eruption rates can generate clasts with similar vesicularities to their subaerial counterparts. A minor proportion of Healy and Raoul SW clasts also show a pink oxidation color, suggesting that hot clasts met air despite 0.5 to >1 km of intervening water. In contrast, Macauley dredged samples have a bimodal density spectrum dominated by clasts formed in a submarine-eruptive style that is not highly explosive. Macauley dredged pyroclasts are also the mixed products of multiple eruptions, as shown by pumice major-element chemistry, and the sea-floor deposits reflect complex volcanic and sedimentation histories. The Kermadec calderas are composite features, and wide dispersal of pumice does not require large single eruptions. When coupled with chemical constraints and textural observations, density spectra are useful for interpreting both eruptive style and the diversity of samples collected from the submarine environment.

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Citation

Barker, Simon J., Rotella, Melissa D., Wilson, Colin J.N., Wright, Ian C. and Wysoczanski, Richard J. (2012) Contrasting pyroclast density spectra from subaerial and submarine silicic eruptions in the Kermadec arc: implications for eruption processes and dredge sampling Bulletin of Volcanology, 74, (6), pp. 1425-1443. (doi:10.1007/s00445-012-0604-2).

More information

Published date: August 2012
Keywords: Submarine volcanism, Explosive eruption, Kermadec arc, Pumice
Organisations: Marine Geoscience

Identifiers

Local EPrints ID: 337716
URI: http://eprints.soton.ac.uk/id/eprint/337716
ISSN: 0258-8900
PURE UUID: b4cde035-87e7-49e3-be30-6817c3ea9428

Catalogue record

Date deposited: 02 May 2012 08:43
Last modified: 18 Jul 2017 06:01

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Contributors

Author: Simon J. Barker
Author: Melissa D. Rotella
Author: Colin J.N. Wilson
Author: Ian C. Wright
Author: Richard J. Wysoczanski

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