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Complex circular subsidence structures in tephra deposited on large blocks of ice: Varða tuff cone, Öræfajökull, Iceland

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posted on 18.05.2017, 13:27 by John L. Smellie, A. J. Walker, D. W. McGarvie, R. Burgess
Several broadly circular structures up to 16 m in diameter, into which higher strata have sagged and locally collapsed, are present in a tephra outcrop on southwest Öræfajökull, southern Iceland. The tephra was sourced in a nearby basaltic tuff cone at Varða. The structures have not previously been described in tuff cones, and they probably formed by the melting out of large buried blocks of ice emplaced during a preceding jökulhlaup that may have been triggered by a subglacial eruption within the Öræfajökull ice cap. They are named ice-melt subsidence structures, and they are analogous to kettle holes that are commonly found in proglacial sandurs and some lahars sourced in ice-clad volcanoes. The internal structure is better exposed in the Varða examples because of an absence of fluvial infilling and reworking, and erosion of the outcrop to reveal the deeper geometry. The ice-melt subsidence structures at Varða are a proxy for buried ice. They are the only known evidence for a subglacial eruption and associated jökulhlaup that created the ice blocks. The recognition of such structures elsewhere will be useful in reconstructing more complete regional volcanic histories as well as for identifying ice-proximal settings during palaeoenvironmental investigations.

History

Citation

Bulletin of Volcanology, 2016, 78:56

Author affiliation

/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Geology

Version

VoR (Version of Record)

Published in

Bulletin of Volcanology

Publisher

Springer Verlag for International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI)

issn

0258-8900

eissn

1432-0819

Acceptance date

15/06/2016

Copyright date

2016

Available date

18/05/2017

Publisher version

https://link.springer.com/article/10.1007/s00445-016-1048-x

Language

en

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