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Particle comminution defines megaflood and superflood energetics

Particle comminution defines megaflood and superflood energetics
Particle comminution defines megaflood and superflood energetics
The concept of ‘megafloods’ and ‘superfloods’ was introduced at the end of the last century to define exceptionally large-discharge floods, primarily those associated with the failure of Quaternary ice-dams. These floods exceeded, by one or two magnitudes, historically recorded floods, megafloods having peak discharges equalling, or exceeding, 1 M m3s-1. Herein, the sediment associations of exceptional floods are found to be distinctive, being dominated by comminuted (smashed) grain-size distributions, which contrast to the sediment deposits of more moderate floods. A consideration of the energetics of moderate floods, superfloods and megafloods with respect to the entrainment, dis-entrainment, suspension and comminution of coarse gravel allows thresholds of energy expenditure to be proposed that reflect general transformations in flood behaviour that relate to distinctive flood deposits. A threshold of energy expenditure - 20 kJ s-1 m-2 - is proposed to separate moderate floods from superfloods; the latter by this definition can be ~ 0.1 M m3s-1. This threshold separates floods competent to entrain cobbles and boulders (with limited comminution of the load) from superfloods that comminute the suspended cobbles and boulders to produce fine granules in suspension. The granules are subsequently deposited to form distinct depositional units that are characteristic of superfloods and megafloods. The energetic threshold is consistent with the lower range of power expenditures associated with the original definition of a megaflood in terms of peak fluid flux.
Megafloods, communition, flood energetics, streampower
0012-8252
Carling, Paul
8d252dd9-3c88-4803-81cc-c2ec4c6fa687
Fan, Xuanmei
04ff993f-9188-455a-8a18-5f2735901aaf
Carling, Paul
8d252dd9-3c88-4803-81cc-c2ec4c6fa687
Fan, Xuanmei
04ff993f-9188-455a-8a18-5f2735901aaf

Carling, Paul and Fan, Xuanmei (2020) Particle comminution defines megaflood and superflood energetics. Earth-Science Reviews, [103087]. (doi:10.1016/j.earscirev.2020.103087).

Record type: Article

Abstract

The concept of ‘megafloods’ and ‘superfloods’ was introduced at the end of the last century to define exceptionally large-discharge floods, primarily those associated with the failure of Quaternary ice-dams. These floods exceeded, by one or two magnitudes, historically recorded floods, megafloods having peak discharges equalling, or exceeding, 1 M m3s-1. Herein, the sediment associations of exceptional floods are found to be distinctive, being dominated by comminuted (smashed) grain-size distributions, which contrast to the sediment deposits of more moderate floods. A consideration of the energetics of moderate floods, superfloods and megafloods with respect to the entrainment, dis-entrainment, suspension and comminution of coarse gravel allows thresholds of energy expenditure to be proposed that reflect general transformations in flood behaviour that relate to distinctive flood deposits. A threshold of energy expenditure - 20 kJ s-1 m-2 - is proposed to separate moderate floods from superfloods; the latter by this definition can be ~ 0.1 M m3s-1. This threshold separates floods competent to entrain cobbles and boulders (with limited comminution of the load) from superfloods that comminute the suspended cobbles and boulders to produce fine granules in suspension. The granules are subsequently deposited to form distinct depositional units that are characteristic of superfloods and megafloods. The energetic threshold is consistent with the lower range of power expenditures associated with the original definition of a megaflood in terms of peak fluid flux.

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Accepted/In Press date: 13 January 2020
e-pub ahead of print date: 15 January 2020
Keywords: Megafloods, communition, flood energetics, streampower

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Local EPrints ID: 437614
URI: http://eprints.soton.ac.uk/id/eprint/437614
ISSN: 0012-8252
PURE UUID: 7f4533a4-894e-465a-a066-547306e10077

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Date deposited: 06 Feb 2020 17:32
Last modified: 15 Jan 2021 05:01

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