Letter | Published:

Highly vesicular pumice generated by buoyant detachment of magma in subaqueous volcanism

Nature Geoscience volume 6, pages 129132 (2013) | Download Citation

Abstract

Many submarine caldera volcanoes are blanketed with deposits of highly vesicular pumice, typically attributed to vigorous explosive activity1,2,3,4. However, it is challenging to relate volcanic products to specific eruptive styles in submarine volcanism5,6. Here we document vesicularity and textural characteristics of pumice clasts dredged from the submarine Macauley volcano in the Kermadec arc, southwest Pacific Ocean. We find that clasts show a bimodal distribution, with corresponding differences in vesicle abundances and shapes. Specifically, we find a sharp mode at 91% vesicularity and a broad mode at 65–80%. Subordinate clasts show gradients in vesicularity. We attribute the bimodality to a previously undocumented eruptive style that is neither effusive nor explosive. The eruption rate is insufficient to cause magma to fragment explosively, yet too high to passively feed a lava dome. Instead, the magma foam buoyantly detaches at the vent and rises as discrete magma parcels, or blebs, while continuing to vesiculate internally. The blebs are widely distributed by ocean currents before they disintegrate or become waterlogged. This disintegration creates individual clasts from interior and rim fragments, yielding the bimodal vesicularity characteristics. We conclude that the generation and widespread dispersal of highly vesicular pumice in the marine environment does not require highly explosive activity.

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Acknowledgements

We thank the Master and crew of the R/V Tangaroa for logistics on the TAN0706 voyage, and the Royal Society of New Zealand Marsden Fund (VUW0613) for financial support. S. Allen, R. Carey, J. McPhie, B. Houghton, R. Wysoczanski and J. White contributed advice, discussions and comments at various stages of this study. We would like to thank L. Gurioli, H. Wright and U. Kueppers for their helpful reviews.

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Affiliations

  1. School of Geography, Environment and Earth Sciences, Victoria University of Wellington, PO Box 600, Wellington 6140, New Zealand

    • Melissa D. Rotella
    • , Colin J. N. Wilson
    •  & Simon J. Barker
  2. National Oceanography Centre, University of Southampton Waterfront Campus, Southampton SO14 3ZH, UK

    • Ian C. Wright

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Contributions

M.D.R. conceived the model and undertook imagery collection and vesicle textural analysis and interpretation. S.J.B. did the density determinations and assisted with figure design. C.J.N.W. and I.C.W. organized the voyage and collected samples with M.D.R. All authors contributed to writing the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Melissa D. Rotella.

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DOI

https://doi.org/10.1038/ngeo1709

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