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Atmospheric processes affecting the separation of volcanic ash and SO2 in volcanic eruptions: Inferences from the May 2011 Grímsvötn eruption

Research output: Contribution to journalArticle

  • Fred Prata
  • Mark J Woodhouse
  • Herbert E Huppert
  • Andrew Prata
  • TH Thordarson
  • Simon A. Carn
Original languageEnglish
Pages (from-to)10709–10732
Number of pages24
JournalAtmospheric Chemistry and Physics
Volume17
Issue number17
Early online date12 Sep 2017
DOIs
DateAccepted/In press - 10 Jul 2017
DateE-pub ahead of print - 12 Sep 2017
DatePublished (current) - Sep 2017

Abstract

The separation of volcanic ash and sulfur dioxide (SO2) gas is sometimes observed during volcanic eruptions. The exact conditions under which separation occurs are not fully understood but the phenomenon is of importance because of the effects volcanic emissions have on aviation, on the environment, and on the earth’s radiation balance. The eruption of Grímsvötn, a subglacial volcano under the Vatnajökull glacier in Iceland during 21–28 May 2011 produced one of the most spectacular examples of ash and SO2 separation, which led to errors in the forecasting of ash in the atmosphere over northern Europe. Satellite data from several sources coupled with meteorological wind data and photographic evidence suggest that the eruption column was unable to sustain itself, resulting in a large deposition of ash, which left a low-level ash-rich atmospheric plume moving southwards and then eastwards towards the southern Scandinavian coast and a high-level predominantly SO2 plume travelling northwards and then spreading eastwards and westwards. Here we provide observational and modelling perspectives on the separation of ash and SO2 and present quantitative estimates of the masses of ash and SO2 that erupted, the directions of transport, and the likely impacts. We hypothesise that a partial column collapse or “sloughing” fed with ash from pyroclastic density currents (PDCs) occurred during the early stage of the eruption, leading to an ash-laden gravity intrusion that was swept southwards, separated from the main column. Our model suggests that water-mediated aggregation caused enhanced ash removal because of the plentiful supply of source water from melted glacial ice and from entrained atmospheric water. The analysis also suggests that ash and SO2 should be treated with separate source terms, leading to improvements in forecasting the movement of both types of emissions.

    Research areas

  • Atmospheric processes, Volcanic eruptions, Volcanic ash, Sulphur dioxide

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    Rights statement: This is the final published version of the article (version of record). It first appeared online via Copernicus at https://www.atmos-chem-phys.net/17/10709/2017/. Please refer to any applicable terms of use of the publisher.

    Final published version, 12 MB, PDF document

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    Rights statement: This is the final published version of the article (version of record). It first appeared online via Copernicus at https://www.atmos-chem-phys.net/17/10709/2017/. Please refer to any applicable terms of use of the publisher.

    Final published version, 55 KB, PDF document

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  • Supplementary information PDF 1

    Rights statement: This is the final published version of the article (version of record). It first appeared online via Copernicus at https://www.atmos-chem-phys.net/17/10709/2017/. Please refer to any applicable terms of use of the publisher.

    Final published version, 3 MB, PDF document

    Licence: CC BY

  • Supplementary information PDF 2

    Rights statement: This is the final published version of the article (version of record). It first appeared online via Copernicus at https://www.atmos-chem-phys.net/17/10709/2017/. Please refer to any applicable terms of use of the publisher.

    Final published version, 9 MB, PDF document

    Licence: CC BY

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