DUNE FOSSILE
Une dune est un relief ou un modelé composé de sable.
Les ensembles dunaires font partie des formations superficielles (formations qui sont relativement récentes à l'échelle géologique). Il existe des dunes littorales et continentales et hydrauliques de tailles, de superficie, d'âges et de dynamiques variés.
Les processus éoliens ou hydrauliques gouvernent l'édification, l'évolution, les mouvements des dunes et des massifs dunaires et définissent les formes générales et de détails (modelés). D'autres appellations qualifient les ensembles dunaires comme erg, dune littorale, croc, garenne, etc. Ces termes généralement locaux peuvent connaître un usage plus général et qualifier un type particulier de dune. Le mot dune vient d'un mot néerlandais duin : colline. Toutes les dunes étant composées de sable, on ne parle pas de "dune de sable", sauf pour préciser la qualité du sable qui la compose : "dune de sable blanc". Contrairement aux autres dunes, la dune fossile ne reçoit plus de sable ni de coquillages car elle n'est plus en bord de mer.
-------------------------------------------
In physical geography, a dune is a hill of sand built either by wind or water flow.
In physical geography, a dune is a hill of sand built either by wind or water flow.
Dunes occur in different forms and sizes, formed by interaction with the flow of air or water. Most kinds of dunes are longer on the windward side where the sand is pushed up the dune and have a shorter "slip face" in the lee of the wind. The valley or trough between dunes is called a slack. A "dune field" is an area covered by extensive sand dunes. Large dune fields are known as ergs. Some coastal areas have one or more sets of dunes running parallel to the shoreline directly inland from the beach. In most cases the dunes are important in protecting the land against potential ravages by storm waves from the sea. Although the most widely distributed dunes are those associated with coastal regions, the largest complexes of dunes are found inland in dry regions and associated with ancient lake or sea beds. Dunes also form under the action of water flow (fluvial processes), and on sand or gravel beds of rivers, estuaries and the sea-bed. The modern word "dune" came into English from French circa 1790. In ancient times, words cognate to "dune" probably had the meaning of a built-up hill or citadel fortification.