Field evidence and hydraulic modeling of a large Holocene jökulhlaup at Jökulsá á Fjöllum channel, Iceland

Howard, Douglas A.; Luzzadder–Beach, Sheryl; Beach, Timothy

doi:10.1016/j.geomorph.2011.07.031

Cited by 11 publications

(50 citation statements)

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“…In light of the claim by Howard et al (2012) of new and extraordinary evidence, the most important of which is 'large boulders', we will herein firstly critically review the landscape upon which evidence of Holocene Jökulsá á Fjöllum jökulhlaups is superimposed. We will then highlight the production and redistribution …”

Section: Discussion Of Research On Jökulsá á Fjöllum Jökulhlaupsmentioning

confidence: 99%

“…They propose that this flood was the largest on Earth. We consider that the magnitude of the jökulhlaup proposed by Howard et al (2012) warrants much more robust field evidence and demands more carefully parameterised hydraulic modelling. For these reasons we firstly (i) present their study in the context of previous research (ii) highlight issues with attributing landforms and sediments to jökulhlaups, and (iii) consider uncertainty regarding the timing and magnitude of jökulhlaups along the Jökulsá á Fjöllum.…”

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confidence: 94%

“…We therefore briefly review the field evidence for, and research into, Jökulsá a Fjöllum jökulhlaups. Given the emphasis placed on the exceptional magnitude of the flood and on the applicability of the work for studies on Mars, we also feel that it is very important to question several assumptions that Howard et al (2012) relied upon for their calculations. This paper therefore proceeds to discuss these assumptions, namely that: isolated large 'erratic' boulders are the product of jökulhlaup deposition, that the position and location of the boulders are sufficient to parameterise a step-backwater hydraulic model, that a hill named 'Ferjufjall' must have been overtopped, that Manning's n can be treated as a fixed quantity, that modelling a single reach of the Jökulsá á Fjöllum can generate meaningful results, and finally that the volume of water implied by such a large peak discharge could have been sourced from northern Vatnajökull.…”

Section: Introductionmentioning

confidence: 99%

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This paper discusses Howard et al (2012) who reconstruct the peak discharge of a glacial outburst flood, or 'jökulhlaup', for part of the Jökulsá á Fjöllum in north-central Iceland. They propose that this flood was the largest on Earth.

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confidence: 99%

“…Secondly, we critically discuss (iv) the major underlying assumptions of their study, and (v) their calculations and subsequent interpretations. These assessments lead us to consider that the proposal by Howard et al (2012) of the largest flood on Earth is highly unrealistic, especially when due consideration is given to a possible source area and a trigger mechanism.© 2012 Elsevier B.V. All rights reserved. …”

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Discussion of ‘Field evidence and hydraulic modeling of a large Holocene jökulhlaup at Jökulsá á Fjöllum channel, Iceland’ by Douglas Howard, Sheryl Luzzadder-Beach and Timothy Beach, 2012

Carrivick¹,

Tweed²,

Carling³

et al. 2013

Geomorphology

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This paper discusses Howard et al. (2012) who reconstruct the peak discharge of a glacial outburst flood, or 'jökulhlaup', for part of the Jökulsá á Fjöllum in north-central Iceland. They propose that this flood was the largest on Earth. We consider that the magnitude of the jökulhlaup proposed by Howard et al. (2012) warrants much more robust field evidence and demands more carefully parameterised hydraulic modelling. For these reasons we firstly (i) present their study in the context of previous research (ii) highlight issues with attributing landforms and sediments to jökulhlaups, and (iii) consider uncertainty regarding the timing and magnitude of jökulhlaups along the Jökulsá á Fjöllum. We argue herein that whilst a range of landforms and sediments that are attributable to jökulhlaups can be observed along the Jökulsá á Fjöllum, these are not necessarily diagnostic of jökulhlaups. Secondly, we critically discuss (iv) the major underlying assumptions of their study, and (v) their calculations and subsequent interpretations. These assessments lead us to consider that the proposal by Howard et al. (2012) of the largest flood on Earth is highly unrealistic, especially when due consideration is given to a possible source area and a trigger mechanism.© 2012 Elsevier B.V. All rights reserved. IntroductionHoward et al. (2012) suggested that a glacial outburst flood or 'jökulhlaup' that routed along the Jökulsá á Fjöllum in northern Iceland during the early Holocene was the largest flood to have occurred on Earth. They present field data, most importantly large boulders, that they attribute to deposition by this flood and they use the elevation of these boulders to drive a hydraulic model that they suggest reasonably represents the characteristics of this flood. However, we feel that the field data as presented in their paper is both ambiguous and insufficient. We therefore briefly review the field evidence for, and research into, Jökulsá a Fjöllum jökulhlaups. Given the emphasis placed on the exceptional magnitude of the flood and on the applicability of the work for studies on Mars, we also feel that it is very important to question several assumptions that Howard et al. (2012) relied upon for their calculations. This paper therefore proceeds to discuss these assumptions, namely that: isolated large 'erratic' boulders are the product of jökulhlaup deposition, that the position and location of the boulders are sufficient to parameterise a step-backwater hydraulic model, that a hill named 'Ferjufjall' must have been overtopped, that Manning's n can be treated as a fixed quantity, that modelling a single reach of the Jökulsá á Fjöllum can generate meaningful results, and finally that the volume of water implied by such a large peak discharge could have been sourced from northern Vatnajökull. Discussion of research on Jökulsá á Fjöllum jökulhlaupsAttributing landforms and sediments to jökulhlaups (Table 1), particularly those jökulhlaups that occurred millennia ago, is far from straight forward and has occupied many m...

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Section: Discussion Of Research On Jökulsá á Fjöllum Jökulhlaupsmentioning

confidence: 99%

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Section: Introductionmentioning

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