ANALYSIS OF BEACH SAND COLOR AND ITS APPLICATION TO SEDIMENTATION

Beach sand color is an important part of the coastal landscape. Some beaches are well known worldwide for their sand color, such as the black and green beaches in Hawaii. Sand color is also an important factor in beach ecology through beach thermal changes. White sandy beaches are usually made of coral and shell. Tan, brown and gray beaches are made of sand trasnported by rivers or the erosion of sandy cliffs. Although the color of a beach depends on the sediment supply budget, sand color has generally not been used for the analysis of beach processes and sedimentation. We pefromed color determination of sand grains collected from 164 sandy beaches with a scanner. The relative frequency of sand color rating was calculated using a color palette based on RGB color and the CIEL*a*b* 1976 color space methods. We determined the relationships between the color characteristics and the geological features of river drainage areas using principle component and cluster analysis. Sandy beaches in Japan were classified into two general groups based on color; gray and brown. The different colors represent the different types of minerals in the grains. The brightness of the sand grains can be explained by the areal ratios of the felsic and mafic rock. Artificial sandy beaches are consist of more colored grains because the color of the imported sediment is different from the native one and the sorting mechanism has not developed. So-callled"singing sand" beaches include many quarts and therefore contain tan and brown grains. The changes of the sand characteristics before and after the Tohoku tsunami in Japan were verified based on sand color information. Noticeable increases were also seen in th sand color brightness and the chromatic on the adjacent sandy beach of 1.4- and the chromatic 4-fold, respectively.