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How do the grain size characteristics of a tephra deposit change over time?

Lookup NU author(s): Dr Nick Cutler, Emily Sear

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This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).


Abstract

Volcanologists frequently use grain size distributions (GSDs) in tephra layers to infer eruption parameters. However, for long-past eruptions, the accuracy of the reconstruction depends upon the correspondence between the initial tephra deposit and preserved tephra layer on which inferences are based. We ask: how closely does the GSD of a decades-old tephra layer resemble the deposit from which it originated? We addressed this question with a study of the tephra layer produced by the eruption of Mount St Helens, USA, in May 1980. We compared grain size distributions from the fresh, undisturbed tephra with grain size measurements from the surviving tephra layer. We found that the overall grainsize characteristics of the tephra layer were similar to the original deposit, and that distinctive features identified by earlier authors had been preserved. However, detailed analysis of our samples showed qualitative differences, specifically a loss of fine material (which we attributed to ‘winnowing’). Understanding how tephra deposits are transformed over time is critical to efforts to reconstruct past eruptions, but inherently difficult to study. We propose long-term, tephra application experiments as a potential way forward.


Publication metadata

Author(s): Cutler N, Streeter RT, Dugmore AJ, Sear ER

Publication type: Article

Publication status: Published

Journal: Bulletin of Volcanology

Year: 2021

Volume: 83

Online publication date: 12/06/2021

Acceptance date: 03/06/2021

Date deposited: 10/06/2021

ISSN (print): 0258-8900

ISSN (electronic): 1432-0819

Publisher: Springer Nature

URL: https://doi.org/10.1007/s00445-021-01469-w

DOI: 10.1007/s00445-021-01469-w


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