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Early-stage aeolian protodunes: bedform development and sand transport dynamics

Early-stage aeolian protodunes: bedform development and sand transport dynamics
Early-stage aeolian protodunes: bedform development and sand transport dynamics
Early-stage aeolian bedforms, or protodunes, are elemental in the continuum of dune development and act as essential precursors to mature dunes. Despite this, we know very little about the processes and feedback mechanisms that shape these nascent bedforms. Whilst theory and conceptual models have offered some explanation for protodune existence and development, until now, we have lacked the technical capability to measure such small bedforms in aeolian settings. Here, we employ terrestrial laser scanning to measure morphological change at the high frequency and spatial resolution required to gain new insights into protodune behaviour. On a 0.06 m high protodune, we observe vertical growth of the crest by 0.005 m in two hours. Our direct measurements of sand transport on the protodune account for such growth, with a reduction in time-averaged sediment flux of 18% observed over the crestal region. Detailed measurements of form also establish key points of morphological change on the protodune. The position on the stoss slope where erosion switches to deposition is found at a point 0.07 m upwind of the crest. This finding supports recent models that explain vertical dune growth through an upwind shift of this switching point. Observations also show characteristic changes in the asymmetric cross section of the protodune. Flow-form feedbacks result in a steepening of the lee slope and a decline in lower stoss slope steepness (by 3°), constituting a reshaping of protodune form towards more mature dune morphology. The approaches and findings applied here, a) demonstrate an ability to quantify processes at requisite spatial and temporal scales for monitoring early-stage dune evolution, b) highlight the crucial role of form-flow feedbacks in enabling early-stage bedform growth, alluding to a fluctuation in feedbacks that require better representation in dune models, and c) provide a new stimulus for advancing understanding of aeolian bedforms.
0197-9337
Baddock, Matthew C.
55f062fc-50a1-4c2d-83ff-a8cc92562346
Nield, Joanna M.
173be2c5-b953-481a-abc4-c095e5e4b790
Wiggs, Giles F.S.
0b574ec8-fcd5-43b8-8b0b-0c84a01499d4
Baddock, Matthew C.
55f062fc-50a1-4c2d-83ff-a8cc92562346
Nield, Joanna M.
173be2c5-b953-481a-abc4-c095e5e4b790
Wiggs, Giles F.S.
0b574ec8-fcd5-43b8-8b0b-0c84a01499d4

Baddock, Matthew C., Nield, Joanna M. and Wiggs, Giles F.S. (2017) Early-stage aeolian protodunes: bedform development and sand transport dynamics Earth Surface Processes and Landforms (doi:10.1002/esp.4242).

Record type: Article

Abstract

Early-stage aeolian bedforms, or protodunes, are elemental in the continuum of dune development and act as essential precursors to mature dunes. Despite this, we know very little about the processes and feedback mechanisms that shape these nascent bedforms. Whilst theory and conceptual models have offered some explanation for protodune existence and development, until now, we have lacked the technical capability to measure such small bedforms in aeolian settings. Here, we employ terrestrial laser scanning to measure morphological change at the high frequency and spatial resolution required to gain new insights into protodune behaviour. On a 0.06 m high protodune, we observe vertical growth of the crest by 0.005 m in two hours. Our direct measurements of sand transport on the protodune account for such growth, with a reduction in time-averaged sediment flux of 18% observed over the crestal region. Detailed measurements of form also establish key points of morphological change on the protodune. The position on the stoss slope where erosion switches to deposition is found at a point 0.07 m upwind of the crest. This finding supports recent models that explain vertical dune growth through an upwind shift of this switching point. Observations also show characteristic changes in the asymmetric cross section of the protodune. Flow-form feedbacks result in a steepening of the lee slope and a decline in lower stoss slope steepness (by 3°), constituting a reshaping of protodune form towards more mature dune morphology. The approaches and findings applied here, a) demonstrate an ability to quantify processes at requisite spatial and temporal scales for monitoring early-stage dune evolution, b) highlight the crucial role of form-flow feedbacks in enabling early-stage bedform growth, alluding to a fluctuation in feedbacks that require better representation in dune models, and c) provide a new stimulus for advancing understanding of aeolian bedforms.

Text Brancaster_protodune_accepted - Accepted Manuscript
Restricted to Repository staff only until 6 October 2018.

More information

Accepted/In Press date: 30 August 2017
e-pub ahead of print date: 6 October 2017

Identifiers

Local EPrints ID: 415373
URI: http://eprints.soton.ac.uk/id/eprint/415373
ISSN: 0197-9337
PURE UUID: e986e48b-fcff-4823-9c03-e7ce61754b17
ORCID for Joanna M. Nield: ORCID iD orcid.org/0000-0002-2657-0525

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Date deposited: 08 Nov 2017 17:30
Last modified: 01 Dec 2017 17:31

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Contributors

Author: Matthew C. Baddock
Author: Joanna M. Nield ORCID iD
Author: Giles F.S. Wiggs

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