Three selected stabilized saucer blowouts in the coast of NW Spain (Iberian Peninsula) are studied under the morphological and sedimentological points of view. The morphologies of these blowouts are characterized: rim, crest, deflation bottom, right (inner and outer) and left (outer and inner) flanks, outer windward and inner lee ward flanks, inner windward and outer lee ward flanks. They are slightly elongated according to the main direction of the prevailing wind. From surficial sand samples, isolines of grain-size parameters such as centile, mean, sorting, skewness, and kurtosis, as well as the mineralogical composition (bioclastic carbonate versus siliciclastic percents) have been considered to establish specific trends. In many cases, isoline contours are adapted to the floor and the sedimentary rim, allowing to deduce the main flow of the wind that contributes to their formation and development of the complex geometry including their granulometry and composition. The average size is coarser in the outer windward and deflation bottom, and minimum in the crest; the sorting is better in the outer lee side and moderate on the bottom; the skewness shows no contrast being only extreme in the inner lee side; less sharp curves are represented on the windward and leeward flanks and crest, and are leptokurtic on the leeward side; carbonate percents are maximum on the outer lee ward side, followed by the bottom, being minimum on the inner windward side. The flank slopes are very high in the outer leeward and internal windward, and moderate in the outer windward and flat in the crest and deflation bottom. A simple model of morphodynamic and sedimentary characterization is proposed, under unidirectional winds.

The embayed beaches of northern Spain’s cliffed, wave-dominated coast contain mixtures of siliciclastic sands, supplied mainly by rivers and coastal erosion, and carbonate bio-clastic sands derived from coastal organisms. The proportion of carbonate material, expressed as a percentage of CaCO₃, is a reliable indicator of the provenance and transport patterns of sediments. This parameter frequently yields more precise information than grain-size analysis. It is well established that the carbonate content typically diminishes in the direction of sediment transport from the original source. At a regional scale, sediment transport along the Cantabrian coast and much of Galicia is predominantly west-to-east, driven by prevailing northwest and west-northwest wave conditions. While large rivers supply abundant siliciclastic sediments, estuaries, rias, mudflats, and marshes contribute nutrients that enhance marine productivity and carbonate production. In the coastal regions of Galicia, the phenomenon of coastal upwelling has been shown to increase biological productivity, thereby fostering the development of carbonate-rich sediments. The skeletal assemblage is classified as bimol-bivalve dominated. Consequently, elevated carbonate percentages are indicative of regions influenced by nutrient-rich upwelling and productive coastal ecosystems. Across approximately 750 km of the Galician and Cantabrian coastline, variations in bioclastic carbonate content help define coastal compartments, identify sediment sources, and infer longshore transport pathways. In the context of the continental shelf, the interplay of opposing currents generated by northern swells, in conjunction with the influence of the rias, exerts a pronounced regulatory effect on the dispersal of sand and the dynamics of the coastline.