New flow relaxation mechanism explains scour fields at the end of submarine channels

This is a Preprint and has not been peer reviewed. The published version of this Preprint is available: https://doi.org/10.1038/s41467-019-12389-x.

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Authors

Florian Pohl , Joris Eggenhuisen , Mike Tilston, Matthieu Cartigny

Abstract

In the ocean, particle-laden gravity flows, turbidity currents, flow in river-like channels across the ocean floor. These submarine channels funnel sediment, nutrients, pollutants and organic carbon into the ocean basins and can extend over 1,000’s of kilometers. At the end of these channels, turbidity currents lose their confinement, decelerate and deposit their sediment load. This is what we read in textbooks. However, sea-floor observations have shown exactly the opposite: turbidity currents are prone to eroding the seafloor upon losing confinement. Such erosion features are commonly linked to a rapid flow transition associated with a hydraulic jump. This hypothesis has not been validated due to a lack of field measurements and scaling problems that prevented erosional turbidity currents to form in physical experiments. Here we use a state-of-the-art scaling method to produce the first experimental turbidity currents that erode upon leaving a channel. The experiments reveal a novel flow mechanism, here called ‘flow relaxation’ that explains the erosion. Flow relaxation is the rapid, internal flow deformation resulting from the loss of confinement, which enhances basal shearing of the turbidity current, thus promoting local scouring. This flow mechanism provides a new explanation of scour formation at the end of channels and its role in the propagation of submarine channel systems.

DOI

https://doi.org/10.31223/osf.io/buknq

Subjects

Earth Sciences, Oceanography, Oceanography and Atmospheric Sciences and Meteorology, Physical Sciences and Mathematics, Sedimentology

Keywords

Dates

Published: 2019-03-11 12:51

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License

CC BY Attribution 4.0 International

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