cette formation de sable, de dunes se forme dans certaines conditions, et cette forme de flêche est très caractéristique. J'ai ajouté "zone" pour préciser que ceci n'est uniquement une dune,
mais une zone sableuse, pouvant parfois être constituée de dunes.

see: ras r'mel at URL below

The definition of "sif (dunaire)" at Wikipédia is not entirely accurate. However, it did give me the English word. They are sharp-crested dunes which "are thought to develop from barchans if a change of wind direction occurs."

Wikipédia - Sif (dunaire)
Le sif est la partie sommitale des dunes. Il sépare la partie en pente douce (pente "au vent") de la partie en pente raide (pente"sous le vent").
http://fr.wikipedia.org/wiki/Sif_(dunaire)

Wikipedia – Dunes – Longitudinal and transverse dunes

Seif dunes.
Longitudinal dunes, also called Seif dunes, elongate parallel to the prevailing wind, possibly caused by a larger dune having its smaller sides blown away. **Seif dunes are sharp-crested** and are common in the Sahara. They range up to 300 m (900 ft) in height and 300 km (200 mi) in length.
***Seif dunes are thought to develop from barchans if a change of wind direction occurs. The new wind direction will lead to the development of a new wing and the over development of one of the original wings. If the prevailing wind then becomes dominant for a lengthy period of time the dune will revert to its barchan form, with one exaggerated wing. Should the strong wind then return the exaggerated wing will further extend so that eventually it will be supplied with sand when the prevailing wind returns. The wing will continue to grow under both wind conditions, thus producing a **seif dune.*** On a seif dune the slip face develops on the side facing away from the strong wind, while the slip face of a barchan faces the direction of movement. In the sheltered troughs between highly developed seif dunes barchans may be formed because the wind is unidirectional.
A transverse dune is perpendicular to the prevailing wind, probably caused by a steady buildup of sand on an already existing minuscule mound.
http://en.wikipedia.org/wiki/Dune

17.5.3 Linear Seif Dunes
A seif, an elongated dune type, is formed under bidirectional wind regimes beating the dune obliquely. Seifs are completely devoid of vegetation and possess a triangular profile with a sharp crest, which explains the term seif (an Arabic word for sword). Another typical characteristic of seifs is the tortuosity of their crest-lines, with their intermittent peaks and saddles (Fig. 17.11).
http://www.boker.org.il/meida/negev/desert_biking/bagnold/Ty...

The Sand Dunes area is unknown even to most Newfoundlanders. This area is the largest sand dune/saltwater-marsh **estuary** ecosystem in Newfoundland. The total area exceeds 10 sq. kms. The sand dunes have occasionally become large enough to appear on charts as the winds and waves have altered their shape. Within the dunefield itself many classic textbook dune forms often occur. Barchans, lunettes, **seif dunes**, and rhourds may periodically be observed. The sand in the dunes (and the adjacent beaches) is derived from pre-existing glacial deposits that were deposited within the last 10,000 years.
http://visitnewfoundland.ca/area.html