Erosion during extreme flood events dominates Holocene canyon evolution in northeast Iceland

Edwin Baynes, Mikael Attal, Samuel Niedermann, Linda Kirstein, Andrew Dugmore, Mark Naylor

Research output: Contribution to journalArticlepeer-review

Abstract

Extreme flood events have the potential to cause catastrophic landscape change in short periods of time (100 – 103 hours). However, their impacts are rarely considered in studies of long-term landscape evolution (> 103 years), because the mechanisms of erosion during such floods are poorly constrained. Here we use topographic analysis and cosmogenic 3He surface exposure dating of fluvially sculpted surfaces to determine the impact of extreme flood events within the Jökulsárgljúfur canyon (North-East Iceland) and to constrain the mechanisms of bedrock erosion during these events. Surface exposure ages allow identification of three periods of intense canyon cutting about 9, 5 and 2 ka ago during which multiple large knickpoints retreated large distances (> 2 km). During these events, a threshold flow depth was exceeded, leading to the toppling and transportation of basalt lava columns. Despite continuing and comparatively large scale (500 m3 s-1) discharge of sediment-rich glacial meltwater, there is no evidence for a transition to an abrasion-dominated erosion regime since the last erosive event because the vertical knickpoints have not diffused over time. We provide a model for the evolution of the Jökulsárgljúfur canyon through the reconstruction of the river profile and canyon morphology at different stages over the last 9 ka and highlight the dominant role played by extreme flood events in the shaping of this landscape during the Holocene.
Original languageEnglish
Pages (from-to)2355–2360
Number of pages6
JournalProceedings of the National Academy of Sciences
Volume112
Issue number8
Early online date9 Feb 2015
DOIs
Publication statusPublished - 24 Feb 2015

Keywords

  • bedrock erosion
  • extreme floods
  • knickpoints
  • Iceland
  • cosmogenic He-3
  • PRODUCTION-RATES
  • RIVER INCISION
  • BEDROCK
  • JOKULHLAUP
  • MEGAFLOOD
  • FJOLLUM
  • JOKULSA
  • CHANNEL
  • ROCK
  • REEVALUATION

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