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Does sand promote or hinder the mobility of cohesive sediment gravity flows?

Baker, Megan L.; Baas, Jaco H.

Does sand promote or hinder the mobility of cohesive sediment gravity flows? Thumbnail


Jaco H. Baas


Sediment gravity flows exhibit a large range of flow behaviours, making their flow dynamics hard to predict and the resulting deposits a challenge to interpret. Cohesive sediment gravity flows containing clay are particularly complex, as their behaviour is controlled by the balance of turbulent and cohesive forces. A first set of laboratory lock-exchange experiments investigated the effect of adding 25% very fine sand by volume to high-density cohesive sediment gravity flows with strongly suppressed turbulence. This caused these mixed clay–sand flows to become more cohesive, have shorter runout distances, and have lower head velocities than the original pure-clay flows, despite the increase in density difference and the non-cohesive properties of the sand. Yield stress measurements confirmed that adding the non-cohesive very fine sand increases the cohesive strength of dense clay suspensions. This higher cohesive strength outcompetes the enhanced density difference and reduces the flow mobility. A second set of experiments across a larger range of clay concentrations showed that, for low-density cohesive sediment gravity flows dominated by turbulent mixing, the addition of 25% very fine sand increased the head velocities because of the enhanced density difference and weak cohesive forces. Thus, the addition of very fine sand may increase or decrease the mobility of cohesive sediment gravity flows, depending on the initial type of flow and the balance between turbulent and cohesive forces. In the natural environment, this study proposes that very fine sand can only increase the cohesive strength and reduce the flow mobility of cohesive sediment gravity flows that have a sufficiently strong matrix strength to fully support the sand particles. The contribution of very fine sand to the cohesive strength of high-density cohesive sediment gravity flows may have important implications for flow transformation on submarine fans, especially in distal regions where transient–turbulent, cohesive flows are particularly common.


Baker, M. L., & Baas, J. H. (in press). Does sand promote or hinder the mobility of cohesive sediment gravity flows?. Sedimentology,

Journal Article Type Article
Acceptance Date Dec 20, 2022
Online Publication Date Feb 20, 2022
Deposit Date Feb 22, 2023
Publicly Available Date Feb 22, 2023
Journal Sedimentology
Electronic ISSN 1365-3091
Publisher Wiley
Peer Reviewed Peer Reviewed


Published Journal Article (5.5 Mb)

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Copyright Statement
&copy; 2022 The Authors. Sedimentology published by John Wiley &amp; Sons Ltd on behalf of International Association of Sedimentologists.<br /> <br /> This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

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