AEOLIAN SAND GEODYNAMICS IN THE NORTH-WES TERN SAHARA - RELATIONS BETWEEN AEROLOGY AND GEOMORPHOLOGY

Aeolian sand migrations were studied in two areas of the North-Western Sahara Desert: the Southern piedmont of the Sahara Atlas and the ''Sa nd River'' of Cape Juby, on the Atlantic shore of the Sahara. Research was conducted on several years of wind data, as well as on field stud y, photointerpretation and remote sensing of dune fields. Aerologic da ta were processed with B. Choppy's software, SABLE, which converts win d data into potential displacement coefficients of the aeolian sands. With the vectorial combination of the displacement coefficient in all possible directions, one obtains a resultant vector, which gives the m igration direction of the sand, as well as the migration coefficient, the ratio between the arithmetic sum of the displacement coefficients and their resultant. These coefficients are themselves transposed in v olume and mass of displaced sand. The similitude between the field dat a and the results obtained by calculation results is remarkable for bo th areas under study. A new scale for the study of dune forms is propo sed : when the sand sources have a precise limit, the edges of the dun e fields indicate the sand migration directions, even in areas where t hese directions are not pronounced. They can thus be used in the study of the current and past displacements of sand and in palaeoclimatic r econstructions.