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Architectural analysis of a volcaniclastic jökulhlaup deposit, southern Iceland: sedimentary evidence for supercritical flow

Lookup NU author(s): Professor Andrew RussellORCiD


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The 1918 eruption of the glacially capped Katla volcano, southern Iceland, generated a violent jökulhlaup, or glacial outburst flood, inundating a large area of Mýrdalssandur, the proglacial outwash plain, where it deposited ca 1km 3 of volcaniclastic sediment. The character of the 1918 jökulhlaup is contentious, having been variously categorized as a turbulent water flow, a hyperconcentrated flow or as a debris flow, based on localized outcrop analysis. In this study, outcrop-based architectural analyses of the 1918 deposits reveal the presence of lenticular and tabular bedsets associated with deposition from quasi-stationary antidunes and down-current migrating antidunes, and from regular based bedsets, associated with transient chute-and-pool bedforms, all of which are associated with turbulent, transcritical to supercritical water flow conditions. Antidune wavelengths range from 24 to 96 m, corresponding to flow velocities of 6 to 12 m sec-1 and average flow depths of 5 to 19 m. This range of calculated flow velocities is in good agreement with estimates made from eyewitness accounts. Architectural analysis of the 1918 jökulhlaup deposits has led to an improved estimation of flow parameters and flow hydraulics associated with the 1918 jökulhlaup that could not have been achieved through localized outcrop analysis. The observations presented here provide additional sedimentological and architectural criteria for the recognition of deposits associated with transcritical and supercritical water flow conditions. The physical scale of sedimentary architectures associated with the migration of bedforms is largely dependent on the magnitude of the formative flow events or processes; sedimentary analyses must therefore be undertaken at the appropriate physical scale if reliable interpretations, regarding modes of deposition and formative flow hydraulics, are to be made. © 2007 The Authors. Journal compilation © 2007 International Association of Sedimentologists.

Publication metadata

Author(s): Duller RA, Mountney NP, Russell AJ, Cassidy NC

Publication type: Article

Publication status: Published

Journal: Sedimentology

Year: 2008

Volume: 55

Issue: 4

Pages: 939-964

ISSN (print): 0037-0746

ISSN (electronic): 1365-3091

Publisher: Wiley-Blackwell Publishing Ltd.


DOI: 10.1111/j.1365-3091.2007.00931.x


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