A General Model for the Helical Structure of Geophysical Flows in Channel Bends

M Azpiroz‐Zabala,M J B Cartigny,D R Parsons,E J Sumner,M A Clare,P J Talling,C Cooper

doi:10.1002/2017gl075721

M Azpiroz‐Zabala, M J B Cartigny + Show 5 more

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https://doi.org/10.1002/2017gl075721

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Abstract

AbstractMeandering channels formed by geophysical flows (e.g., rivers and seafloor turbidity currents) include the most extensive sediment transport systems on Earth. Previous measurements from rivers show how helical flow at meander bends plays a key role in sediment transport and deposition. Turbidity currents differ from rivers in both density and velocity profiles. These differences, and the lack of field measurements from turbidity currents, have led to multiple models for their helical flow around bends. Here we present the first measurements of helical flow in submarine turbidity currents. These 10 flows lasted for 1–10 days, were up to ~80 m thick, and displayed a consistent helical structure. This structure comprised two vertically stacked cells, with the bottom cell rotating in the opposite direction to helical flow in rivers. Furthermore, we propose a general model that predicts the range of helical flow structures observed in rivers, estuaries, and turbidity currents based on their density stratification.

Highlights

Extensive submarine channels transport billions of tonnes of sediment for hundreds of kilometers, to form vast sedimentary deposits in the deep sea (Normark, 1970; Savoye et al, 2009; Shepard, 1933)
We propose a general model that predicts the range of helical flow structures observed in rivers, estuaries, and turbidity currents based on their density stratification
The largest submarine fans are fed by highly sinuous submarine channels, suggesting that meander bends may enhance sediment transport distances (Pirmez & Imran, 2003; Straub et al, 2008)

Summary

Introduction

Extensive submarine channels transport billions of tonnes of sediment for hundreds of kilometers, to form vast sedimentary deposits (called submarine fans) in the deep sea (Normark, 1970; Savoye et al, 2009; Shepard, 1933). There are few direct observations of deep-sea turbidity currents (Cooper et al, 2016; Khripounoff et al, 2003; Talling et al, 2015; Vangriesheim et al, 2009). Before collection of this data set (Azpiroz-Zabala et al, 2017; Cooper et al, 2013), there were no detailed (subminute) measurements from within a meander bend in the deep sea. Our understanding of meandering deep-sea channels was based on laboratory-scale experiments and numerical modeling, or on comparisons to rivers, estuaries, and saline density flows

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