Great Holocene Floods along Jökulsá á Fjöllum, North Iceland

  1. I. Peter Martini2,
  2. Victor R. Baker3 and
  3. Guillermina Garzón4
  1. R. B. Waitt

Published Online: 17 MAR 2009

DOI: 10.1002/9781444304299.ch3

Flood and Megaflood Processes and Deposits: Recent and Ancient Examples

Flood and Megaflood Processes and Deposits: Recent and Ancient Examples

How to Cite

Waitt, R. B. (2002) Great Holocene Floods along Jökulsá á Fjöllum, North Iceland, in Flood and Megaflood Processes and Deposits: Recent and Ancient Examples (eds I. P. Martini, V. R. Baker and G. Garzón), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304299.ch3

Editor Information

  1. 2

    Department of Land Resource Science, University of Guelph, Guelph, Ontario, Canada

  2. 3

    Department of Hydrology and Water Resources, University of Arizona, Tucson, AZ 85721–0011, USA

  3. 4

    Dpto de Geodinámica, Fac. de Geología, Universidad of Complutense, 28040 Madrid, Spain

Author Information

  1. U.S. Geological Survey, 5400 MacArthur Blvd., Vancouver, WA 98661, USA

Publication History

  1. Published Online: 17 MAR 2009
  2. Published Print: 10 FEB 2002

ISBN Information

Print ISBN: 9780632064045

Online ISBN: 9781444304299

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Keywords:

  • Great Holocene floods along Jökulsá á Fjöllum, north Iceland;
  • Weichsel glaciation and postglacial volcanism;
  • lower Jökulsá valley and Ásbyrgi area;
  • holocene rifts and volcanism;
  • preflood Jökulsá canyon;
  • early and middle holocene floods, lower jökulsá;
  • many floods 8000–4000 yr BP;
  • late holocene flood

Summary

Jökulsá á Fjöllum, Iceland's largest glacial river, drains from Vatnajökull icecap northward to the sea along a broad low that includes an active volcanic belt. Geomorphic features along this path reveal an ancient discharge of water large enough to fill the river valley and spill among a plexus of lows in the volcanic landscape. Stratigraphy in most places reveals just one late Holocene great flood down Jökulsá á Fjöllum, between 2500 and 2000 yr ago. Step-backwater computation suggests its peak flow was 0.7 million m3/s or more. An early scabland-carving great flood had swept down the Ásbyrgi area of lowermost Jökulsá just after deglaciation, 9000–8000 yr ago. Stratigraphy near Vesturdalur reveals at least 16 additional floods, perhaps of moderate discharge, between about 8000 and 4000 yr ago.

Dispersed field evidence of the late Holocene great flood–anastomosing channels whose basalt surfaces are water fluted and half-potholed, in places plucked down to small-scale scabland replete with dry cataracts, huge boulders, long gravel bars, giant current dunes—is traced the length of Jökulsá valley. From Vatnajökull's north margin at Kverkfjöll, water anastomosed through diverse lows of a high-relief landscape. Thus swift release of meltwater from subglacial Kverkfjöll caldera must have been a source of flood. But even this catastrophic outflow was insufficient to constitute the huge discharges evident farther downvalley. Field evidence reveals a yet greater discharge directly from the large outlet glacier Dyngjujökull. There is no evidence that subglacial Bárðarbunga caldera was involved, but subglacial melting during eruption of a more eastern fissure system could be a source of flood.