气候变化领域集成服务门户(CCPortal): Particle comminution defines megaflood and superflood energetics

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DOI	10.1016/j.earscirev.2020.103087
	Particle comminution defines megaflood and superflood energetics
	Carling P.A.; Fan X.
发表日期	2020
ISSN	00128252
卷号	204
英文摘要	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 m3 s−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 m3 s−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. Significance: Exceptional floods occurred in prehistoric times; the largest are referred to as ‘megafloods’ or ‘superfloods’. To distinguish such exceptional floods from other large floods, megafloods were defined as having a peak discharge exceeding 1 M m3 s−1. However, many reports of ‘megafloods’ are flows with a peak discharge smaller than 1 M m3 s−1. Recent research has shown that megafloods and superfloods deposit distinctive layers of smashed gravel, which is not the case for smaller floods. The gravel is smashed by exceptionally high-energy expenditures. Consideration of the energetics of floods to transport gravel allows a robust quantitative definition of ‘superflood’ based on the energy needed to smash a range of gravel sizes. © 2020 Elsevier B.V.
关键词	Comminution Energy expenditure Megafloods Prehistoric floods Suspended sediments
英文关键词	comminution; depositional environment; entrainment; flooding; paleoflood; particle motion; particle size; peak discharge; Quaternary; sediment transport; suspended sediment
语种	英语
来源期刊	Earth Science Reviews
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/203657
作者单位	State Key Laboratory of Geohazard Prevention and Geoenvironment Protection, Chengdu University of Technology, Chengdu, Sichuan 610059, China
推荐引用方式 GB/T 7714	Carling P.A.,Fan X.. Particle comminution defines megaflood and superflood energetics[J],2020,204.
APA	Carling P.A.,&Fan X..(2020).Particle comminution defines megaflood and superflood energetics.Earth Science Reviews,204.
MLA	Carling P.A.,et al."Particle comminution defines megaflood and superflood energetics".Earth Science Reviews 204(2020).