Sources of uncertainty in the Mazama isopachs and the implications for interpreting distal tephra deposits from large magnitude eruptions

Hannah M. Buckland; Katharine V. Cashman; Samantha L. Engwell; Alison C. Rust

doi:10.1007/s00445-020-1362-1

Sources of uncertainty in the Mazama isopachs and the implications for interpreting distal tephra deposits from large magnitude eruptions

Hannah M. Buckland
, Katharine V. Cashman
, Samantha L. Engwell
, Alison C. Rust

Continental Scientific Drilling Facility

Research output: Contribution to journal › Article › peer-review

45 Scopus citations

Abstract

Estimating the area of tephra fallout and volume of large magnitude eruptions is fundamental to interpretations of the hazards posed by eruptions of this scale. This study uses the tephra from the caldera forming eruption of Mount Mazama (Crater Lake, OR, USA) to demonstrate the challenges faced when working with large prehistoric tephra deposits and outlines the methodologies required to determine eruption volume and magnitude. We combine > 250 Mazama tephra occurrences, reported by a range of disciplines (including archaeology, paleoclimatology and volcanology), with new field studies to better understand the extent of the distal tephra. We find that the Mazama tephra has been remobilised to varying degrees over the past 7000 years, so each tephra locality was appraised for the likelihood that it records primary tephra fallout. We designated 45 of the distal (> 100 km from source) tephra sites as suitable for use in the production of isopachs using a spline fitting method. The new distal isopachs were then integrated with proximal fallout data and estimates of the ignimbrite volume from previous studies to revise the estimated bulk erupted volume from the climactic Mazama eruption to ~ 176 km³ (~ 61 km³ dense-rock equivalent; DRE). This study demonstrates the importance of collating tephra localities from a range of disciplines and that even remobilised deposits provide valuable information about the extent of the deposit. Interpreting remobilised deposits can provide insight into post-eruptive processes that could potentially pose secondary hazards following large magnitude eruptions. We also show that in some circumstances, remobilised deposits preserve important physical properties such as grain size.

Original language	English (US)
Article number	23
Journal	Bulletin of Volcanology
Volume	82
Issue number	3
DOIs	https://doi.org/10.1007/s00445-020-1362-1
State	Published - Mar 1 2020

Bibliographical note

Funding Information:
H.M.B is supported by a NERC GW4+ Doctoral Training Partnership studentship from the Natural Environment Research Council (NERC; NE/L002434/1) with additional support from the British Geological Survey. S.L.E. publishes with permission of the CEO, British Geological Survey. We would like to acknowledge the numerous researchers whose fieldwork and analysis contributed to the Mazama Locality Database. Thanks to Joanne Egan and John Westgate for sharing their databases of Mazama tephra localities that enabled this study to progress. Further thanks go to Colin Long, Britta Jensen, Mark Shapley and Jack Oviatt who shared their knowledge of Mazama tephra localities with us directly. We also extend a broad thanks to the attendees of the INTAV conference in Romania 2018, where this work was presented initiating many helpful conversations. Fieldwork was carried out with help from Bob Carson, Kirsten Nicolyasen, Danielle McKay and Emily Gottesfeld who are greatly acknowledged. Finally, we thank David Pyle and Stephen Self for their useful reviews, which improved the paper, and associate editor P.-S. Ross for quick and helpful handling.

Publisher Copyright:
© 2020, The Author(s).

Copyright:
Copyright 2020 Elsevier B.V., All rights reserved.

Keywords

Crater Lake
Eruption volume
Isopachs
Mazama
Remobilisation
Tephra

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10.1007/s00445-020-1362-1

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title = "Sources of uncertainty in the Mazama isopachs and the implications for interpreting distal tephra deposits from large magnitude eruptions",

abstract = "Estimating the area of tephra fallout and volume of large magnitude eruptions is fundamental to interpretations of the hazards posed by eruptions of this scale. This study uses the tephra from the caldera forming eruption of Mount Mazama (Crater Lake, OR, USA) to demonstrate the challenges faced when working with large prehistoric tephra deposits and outlines the methodologies required to determine eruption volume and magnitude. We combine > 250 Mazama tephra occurrences, reported by a range of disciplines (including archaeology, paleoclimatology and volcanology), with new field studies to better understand the extent of the distal tephra. We find that the Mazama tephra has been remobilised to varying degrees over the past 7000 years, so each tephra locality was appraised for the likelihood that it records primary tephra fallout. We designated 45 of the distal (> 100 km from source) tephra sites as suitable for use in the production of isopachs using a spline fitting method. The new distal isopachs were then integrated with proximal fallout data and estimates of the ignimbrite volume from previous studies to revise the estimated bulk erupted volume from the climactic Mazama eruption to \textasciitilde{} 176 km3 (\textasciitilde{} 61 km3 dense-rock equivalent; DRE). This study demonstrates the importance of collating tephra localities from a range of disciplines and that even remobilised deposits provide valuable information about the extent of the deposit. Interpreting remobilised deposits can provide insight into post-eruptive processes that could potentially pose secondary hazards following large magnitude eruptions. We also show that in some circumstances, remobilised deposits preserve important physical properties such as grain size.",

keywords = "Crater Lake, Eruption volume, Isopachs, Mazama, Remobilisation, Tephra",

author = "Buckland, \{Hannah M.\} and Cashman, \{Katharine V.\} and Engwell, \{Samantha L.\} and Rust, \{Alison C.\}",

note = "Funding Information: H.M.B is supported by a NERC GW4+ Doctoral Training Partnership studentship from the Natural Environment Research Council (NERC; NE/L002434/1) with additional support from the British Geological Survey. S.L.E. publishes with permission of the CEO, British Geological Survey. We would like to acknowledge the numerous researchers whose fieldwork and analysis contributed to the Mazama Locality Database. Thanks to Joanne Egan and John Westgate for sharing their databases of Mazama tephra localities that enabled this study to progress. Further thanks go to Colin Long, Britta Jensen, Mark Shapley and Jack Oviatt who shared their knowledge of Mazama tephra localities with us directly. We also extend a broad thanks to the attendees of the INTAV conference in Romania 2018, where this work was presented initiating many helpful conversations. Fieldwork was carried out with help from Bob Carson, Kirsten Nicolyasen, Danielle McKay and Emily Gottesfeld who are greatly acknowledged. Finally, we thank David Pyle and Stephen Self for their useful reviews, which improved the paper, and associate editor P.-S. Ross for quick and helpful handling. Publisher Copyright: {\textcopyright} 2020, The Author(s). Copyright: Copyright 2020 Elsevier B.V., All rights reserved.",

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N2 - Estimating the area of tephra fallout and volume of large magnitude eruptions is fundamental to interpretations of the hazards posed by eruptions of this scale. This study uses the tephra from the caldera forming eruption of Mount Mazama (Crater Lake, OR, USA) to demonstrate the challenges faced when working with large prehistoric tephra deposits and outlines the methodologies required to determine eruption volume and magnitude. We combine > 250 Mazama tephra occurrences, reported by a range of disciplines (including archaeology, paleoclimatology and volcanology), with new field studies to better understand the extent of the distal tephra. We find that the Mazama tephra has been remobilised to varying degrees over the past 7000 years, so each tephra locality was appraised for the likelihood that it records primary tephra fallout. We designated 45 of the distal (> 100 km from source) tephra sites as suitable for use in the production of isopachs using a spline fitting method. The new distal isopachs were then integrated with proximal fallout data and estimates of the ignimbrite volume from previous studies to revise the estimated bulk erupted volume from the climactic Mazama eruption to ~ 176 km3 (~ 61 km3 dense-rock equivalent; DRE). This study demonstrates the importance of collating tephra localities from a range of disciplines and that even remobilised deposits provide valuable information about the extent of the deposit. Interpreting remobilised deposits can provide insight into post-eruptive processes that could potentially pose secondary hazards following large magnitude eruptions. We also show that in some circumstances, remobilised deposits preserve important physical properties such as grain size.

AB - Estimating the area of tephra fallout and volume of large magnitude eruptions is fundamental to interpretations of the hazards posed by eruptions of this scale. This study uses the tephra from the caldera forming eruption of Mount Mazama (Crater Lake, OR, USA) to demonstrate the challenges faced when working with large prehistoric tephra deposits and outlines the methodologies required to determine eruption volume and magnitude. We combine > 250 Mazama tephra occurrences, reported by a range of disciplines (including archaeology, paleoclimatology and volcanology), with new field studies to better understand the extent of the distal tephra. We find that the Mazama tephra has been remobilised to varying degrees over the past 7000 years, so each tephra locality was appraised for the likelihood that it records primary tephra fallout. We designated 45 of the distal (> 100 km from source) tephra sites as suitable for use in the production of isopachs using a spline fitting method. The new distal isopachs were then integrated with proximal fallout data and estimates of the ignimbrite volume from previous studies to revise the estimated bulk erupted volume from the climactic Mazama eruption to ~ 176 km3 (~ 61 km3 dense-rock equivalent; DRE). This study demonstrates the importance of collating tephra localities from a range of disciplines and that even remobilised deposits provide valuable information about the extent of the deposit. Interpreting remobilised deposits can provide insight into post-eruptive processes that could potentially pose secondary hazards following large magnitude eruptions. We also show that in some circumstances, remobilised deposits preserve important physical properties such as grain size.

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Sources of uncertainty in the Mazama isopachs and the implications for interpreting distal tephra deposits from large magnitude eruptions

Abstract

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