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Field observations of spatial backshore morphology and sand grain size distribution were conducted at Aotsuka beach facing the Pacific Ocean in Japan, in order to investigate both wave and wind impacts on short-term backshore processes. The sand was coarsened notably just after large waves during a storm in January 2005 in the seaward part of backshore; and then became finer in February. The backshore coarsening processes is most likely explained from the external forces of (i) run-up waves, (ii) strong landward winds, and (iii) mild winds. At first, coarse sand is transported with fine sand to the foreshore or the seaward part of the backshore by wave run-up. Under strong landward winds, both coarse and fine sands are transported landward and sand coarsening occurs in the backshore. On the other hand, under mild winds, only the fine sand is transported and coarsening occurs in the area of the wave run-up. After coarsening, the sand becomes finer due to diffusion of the coarse sand, mixture of coarse and fine sands during transport, or sedimentation of fine sand on the coarse sand. The backshore coarsening occurred under both wave and wind actions.
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