Grain-Size Characteristics of Wind Ripples on a Desert Seif Dune

The grain-size distribution of sand from ripples and megaripples, formed on a desert seif dune in the northern Sinai desert, was analyzed by using a unique method of sampling the surface layer. The dune, on the surface of which the ripples under investigation were formed, is composed of unimodal fine sand. The plinth of the dune is composed of bimodal, fine and medium-grained, sand on which the megaripples form. In both ripples and megaripples, the sand, several centimeters below the surface, is coarser than that of the dune body. The sand of the crest of the ripples and megaripples is coarser than that of the trough. Megaripples are characterized by an armored layer of coarse sand covering the windward slope, which thus makes up the trimodal distribution of megaripple sand. Ripples, however, are composed of unimodal sand and lack an armored surface. It seems that, more than anything else, it is the process of sand grain sorting that affects the wavelength of the ripples and megaripples.