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Phase diagrams of dune shape and orientation depending on sand availability.

Gao X, Narteau C, Rozier O, Courrech du Pont S - Sci Rep (2015)

Bottom Line: New evidence indicates that sand availability does not only control dune type but also the underlying dune growth mechanism and the subsequent dune orientation.These two conditions of sand availability are associated with two independent dune growth mechanisms and, for both of them, we present the complete phase diagrams of dune shape and orientation.There are systematic transitions in dune shape from barchans to linear dunes extending away from the localized sand source, and vice-versa.

View Article: PubMed Central - PubMed

Affiliation: Equipe de Dynamique des Fluides Géologiques, Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Université Paris Diderot, UMR 7154 CNRS, 1 rue Jussieu, 75238 Paris Cedex 05, France.

ABSTRACT
New evidence indicates that sand availability does not only control dune type but also the underlying dune growth mechanism and the subsequent dune orientation. Here we numerically investigate the development of bedforms in bidirectional wind regimes for two different conditions of sand availability: an erodible sand bed or a localized sand source on a non-erodible ground. These two conditions of sand availability are associated with two independent dune growth mechanisms and, for both of them, we present the complete phase diagrams of dune shape and orientation. On an erodible sand bed, linear dunes are observed over the entire parameter space. Then, the divergence angle and the transport ratio between the two winds control dune orientation and dynamics. For a localized sand source, different dune morphologies are observed depending on the wind regime. There are systematic transitions in dune shape from barchans to linear dunes extending away from the localized sand source, and vice-versa. These transitions are captured fairly by a new dimensionless parameter, which compares the ability of winds to build the dune topography in the two modes of dune orientation.

No MeSH data available.


Related in: MedlinePlus

Barchan dunes in a zone of low RDP/DP and σF/σI-values.These dunes are located in a sand corridor between the Badain Jaran and the Tengger deserts (China, 39°23′25′′ N, 102°59′26′′ E, image credit: Google Earth). Inset shows the local sand flux roses. In this area, the mean RDP/DP-value and the flux roses derived from the ERA-Interim data are in agreement with the direct measurements of Zhang et al.38, ten kilometers away from the dunes. The map used in this figure is generated by GMT (The general mapping tools).
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f7: Barchan dunes in a zone of low RDP/DP and σF/σI-values.These dunes are located in a sand corridor between the Badain Jaran and the Tengger deserts (China, 39°23′25′′ N, 102°59′26′′ E, image credit: Google Earth). Inset shows the local sand flux roses. In this area, the mean RDP/DP-value and the flux roses derived from the ERA-Interim data are in agreement with the direct measurements of Zhang et al.38, ten kilometers away from the dunes. The map used in this figure is generated by GMT (The general mapping tools).

Mentions: In the ergs around the Tibesti Massif where linear dunes occur, dunes always roughly align with the resultant sand flux. It indicates that these linear dunes recognized as seifs by Bagnold32 or silks by Mainguet and Callot31 are finger dunes that grow by extension from localized depositional areas. Note that zones of transition in this field coincide to places where the wind tends to be more unidirectional. It corresponds to the transition from barchans to finger dunes when the θ-value increases for a given N-value, which is also captured by the RDP/DP parameter (Fig. 4b). Nevertheless, barchan dunes are not restricted to large RDP/DP values. In agreement with our predictions, barchans can occur in zones of moderate RDP/DP-value, providing that σF/σI is small enough. This is for example the case in sand corridors between the Badain Jaran and the Tengger deserts where two wind components cancel each other (see Fig. 7).


Phase diagrams of dune shape and orientation depending on sand availability.

Gao X, Narteau C, Rozier O, Courrech du Pont S - Sci Rep (2015)

Barchan dunes in a zone of low RDP/DP and σF/σI-values.These dunes are located in a sand corridor between the Badain Jaran and the Tengger deserts (China, 39°23′25′′ N, 102°59′26′′ E, image credit: Google Earth). Inset shows the local sand flux roses. In this area, the mean RDP/DP-value and the flux roses derived from the ERA-Interim data are in agreement with the direct measurements of Zhang et al.38, ten kilometers away from the dunes. The map used in this figure is generated by GMT (The general mapping tools).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4588573&req=5

f7: Barchan dunes in a zone of low RDP/DP and σF/σI-values.These dunes are located in a sand corridor between the Badain Jaran and the Tengger deserts (China, 39°23′25′′ N, 102°59′26′′ E, image credit: Google Earth). Inset shows the local sand flux roses. In this area, the mean RDP/DP-value and the flux roses derived from the ERA-Interim data are in agreement with the direct measurements of Zhang et al.38, ten kilometers away from the dunes. The map used in this figure is generated by GMT (The general mapping tools).
Mentions: In the ergs around the Tibesti Massif where linear dunes occur, dunes always roughly align with the resultant sand flux. It indicates that these linear dunes recognized as seifs by Bagnold32 or silks by Mainguet and Callot31 are finger dunes that grow by extension from localized depositional areas. Note that zones of transition in this field coincide to places where the wind tends to be more unidirectional. It corresponds to the transition from barchans to finger dunes when the θ-value increases for a given N-value, which is also captured by the RDP/DP parameter (Fig. 4b). Nevertheless, barchan dunes are not restricted to large RDP/DP values. In agreement with our predictions, barchans can occur in zones of moderate RDP/DP-value, providing that σF/σI is small enough. This is for example the case in sand corridors between the Badain Jaran and the Tengger deserts where two wind components cancel each other (see Fig. 7).

Bottom Line: New evidence indicates that sand availability does not only control dune type but also the underlying dune growth mechanism and the subsequent dune orientation.These two conditions of sand availability are associated with two independent dune growth mechanisms and, for both of them, we present the complete phase diagrams of dune shape and orientation.There are systematic transitions in dune shape from barchans to linear dunes extending away from the localized sand source, and vice-versa.

View Article: PubMed Central - PubMed

Affiliation: Equipe de Dynamique des Fluides Géologiques, Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Université Paris Diderot, UMR 7154 CNRS, 1 rue Jussieu, 75238 Paris Cedex 05, France.

ABSTRACT
New evidence indicates that sand availability does not only control dune type but also the underlying dune growth mechanism and the subsequent dune orientation. Here we numerically investigate the development of bedforms in bidirectional wind regimes for two different conditions of sand availability: an erodible sand bed or a localized sand source on a non-erodible ground. These two conditions of sand availability are associated with two independent dune growth mechanisms and, for both of them, we present the complete phase diagrams of dune shape and orientation. On an erodible sand bed, linear dunes are observed over the entire parameter space. Then, the divergence angle and the transport ratio between the two winds control dune orientation and dynamics. For a localized sand source, different dune morphologies are observed depending on the wind regime. There are systematic transitions in dune shape from barchans to linear dunes extending away from the localized sand source, and vice-versa. These transitions are captured fairly by a new dimensionless parameter, which compares the ability of winds to build the dune topography in the two modes of dune orientation.

No MeSH data available.


Related in: MedlinePlus