The physics of dunes relies on the interaction between a wind flow and an erodible topography. Thus, if strong enough to transport grains, the wind shapes sandy areas into dune fields. These dunes are reminiscent of a wavy sea so that sandy deserts are called sand seas. However, the comparison stops there. Contrary to water waves, dunes propagate only under wind action and when the wind stops, they do not vanish but stand. Consequently, dunes are not only the result of the present winds, but can integrate the wind regimes over long periods. Thus, they exhibit a range of shapes and sizes with superimposed patterns. They are witnesses of past wind regimes and their shape and orientation are used to constraint climatic models on other planetary bodies where they are observed as well (e.g., Mars, Titan and Venus). Here, we discuss the morphodynamics of dunes and endeavor to identify and to explain the physical mechanisms at play in the selection of their shape, size and orientation, whilst focusing on Earth desert sand dunes.
La physique des dunes repose sur l'interaction entre le vent et une topographie érodable. Quand le vent souffle au-dessus d'une surface de sable, des dunes se forment dès lors que des grains sont transportés. Ces dunes offrent un paysage qui ressemble à une mer mouvementée et les déserts sableux sont appelés des mers de sable. Cependant, l'analogie entre dunes et vagues s'arrête là. Contrairement aux vagues, les dunes ne se propagent que sous l'action du vent, et si le vent s'arrête de souffler, elle ne disparaissent pas, mais persistent. Ces tas de sable ne sont pas seulement le fruit des vents présents, mais peuvent intégrer l'histoire des vents sur de longues périodes. Cette propriété explique la richesse des formes et des échelles observées, et fait des dunes des témoins des vents passés. Ainsi, on utilise leur forme et surtout leur orientation pour contraindre les modèles climatiques des corps célestes comme Titan, Mars ou Vénus, où elles sont observées. Dans cet article, nous expliquons la forme, la taille et l'orientation des dunes en passant en revue la littérature récente et en nous attachant à identifier et à expliquer les mécanismes physiques mis en jeu.
Mots-clés : Dune, Géomorphologie, Désert, Barchane, Transport de sable, Mouvements collectifs
Sylvain Courrech du Pont 1
@article{CRPHYS_2015__16_1_118_0,
author = {Sylvain Courrech du Pont},
title = {Dune morphodynamics},
journal = {Comptes Rendus. Physique},
pages = {118--138},
publisher = {Elsevier},
volume = {16},
number = {1},
year = {2015},
doi = {10.1016/j.crhy.2015.02.002},
language = {en},
}
Sylvain Courrech du Pont. Dune morphodynamics. Comptes Rendus. Physique, Granular physics / Physique des milieux granulaires, Volume 16 (2015) no. 1, pp. 118-138. doi : 10.1016/j.crhy.2015.02.002. https://comptes-rendus.academie-sciences.fr/physique/articles/10.1016/j.crhy.2015.02.002/
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