Controls on the Sedimentology of the November 1996 Jökulhlaup Deposits, SkeiðaráRsandur, Iceland

  1. N. D. Smith3 and
  2. J. Rogers4
  1. A. J. Russell1 and
  2. Ó. Knudsen2

Published Online: 17 MAR 2009

DOI: 10.1002/9781444304213.ch23

Fluvial Sedimentology VI

Fluvial Sedimentology VI

How to Cite

Russell, A. J. and Knudsen, Ó. (1999) Controls on the Sedimentology of the November 1996 Jökulhlaup Deposits, SkeiðaráRsandur, Iceland, in Fluvial Sedimentology VI (eds N. D. Smith and J. Rogers), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304213.ch23

Editor Information

  1. 3

    Department of Geosciences, 214 Bessey Hall, University of Nebraska, Lincoln, NE 68588-0340, USA

  2. 4

    Cape Town, South Africa

Author Information

  1. 1

    Department of Earth Sciences, Keele University, Keele, Staffordshire ST5 5BG, UK

  2. 2

    Klettur Consulting Engineers, Bíldshöfða 12, IS 112 Reykjavík, Iceland

Publication History

  1. Published Online: 17 MAR 2009
  2. Published Print: 7 OCT 1999

ISBN Information

Print ISBN: 9780632053544

Online ISBN: 9781444304213

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Keywords:

  • controls on sedimentology of November 1996 jökulhlaup deposits Skeiðarársandur, Iceland;
  • November 1996 jökulhlaup;
  • volcanic eruption beneath Vatnajökull ice-cap;
  • vertical sedimentary sections;
  • dissected outwash fans on Súla and proximal Gígjukvísl;
  • shallow sections on large proglacial outwash fan;
  • sedimentological controls of jökulhlaup deposits;
  • sediments deposited within backwater zones;
  • Gígjukvísl downstream of moraine constriction;
  • waning-stage sediment reworking

Summary

This paper examines controls on the sedimentology of deposits associated with the spectacular November 1996 jökulhlaup (glacial outburst flood, from the Icelandic ‘jokul’ (glacial) and ‘hlaup’ (outburst) pronounced ‘yow-koul-lauwp’) on the proximal zone of the Skeiðarársandur, Iceland, the world's largest active glacial outwash plain. A volcanic eruption beneath the Vatnajökull ice-cap began on 30 September 1996. On exiting the glacier, jökulhlaup flows coalesced into four main outlets. Flood flows initially included large debris lobes that surged from the glacier margin at velocities of up to 6 m s−1. The main flood, however, was dominated by watery, turbulent runoff. Sections through ice-proximal fans in both the Gígjukvísl and Súla catchments showed distinctive upward-coarsening sequences indicative of rising-limb deposition. These deposits ranged from horizontally bedded sands, gravels, boulders and debris-rich ice blocks indicative of fluvial deposition, to matrix-supported units suggestive of hyperconcentrated and debris-flow deposition. These proximal, non-backwater-affected deposits were characterized by the simultaneous deposition of ice blocks. Matrix-supported sedimentary successions within a large ice-embayment contain large rip-up clasts, deposited rapidly from a high-energy hyperconcentrated flow into a slackwater zone.

Successions within the large Gígjukvísl proglacial outwash fan indicated waning-stage deposition from a hyperconcentrated flow. Late waning-stage ice-block grounding initiated rapid river-bed scour, resulting in the deposition of structureless gravel units indicative of ‘traction carpet’ conditions. Deposition into local backwater areas formed deltaic deposits containing sandy foreset beds up to 5 m in height. Successions downstream of a large backwater zone were dominated by trough and planar cross-stratified sands and gravels, deposited in the lee of both individual and clustered icebergs. In places, sections are capped by sandy, climbing-ripple sequences, indicating rapid waning-stage sedimentation. Sedimentary successions on the Gígjukvísl fan reflect both prolonged flow and continuously high sediment supply, even on the waning stage. In contrast, smaller outlets elsewhere experienced flows of shorter duration, where sediment supply was exhausted prior to flow cessation. The sedimentology of the 1996 jökulhlaup deposits was controlled by:

1 the high sediment concentration of flows exiting the glacier;

2 waning-stage sediment reworking;

3 the influence of large-scale channel geometry;

4 ice-block distribution;

5 flow duration.

The results of this study will allow better interpretation of the sedimentary impact of single high-magnitude jökulhlaups within both active glaciofluvial systems and the sedimentary record of former proglacial areas.