Particle rounding in beach gravels

SUMMARY Splitting, crushing and spalling which occur when boulders move against each other, generate fine material and so give rise to angular large and small sizes. The nature of the rounding process can be deduced from the analysis of moments of the roundness frequency distribution of the size range 4–128 mm. A low standard deviation indicates the dominance of one process—either abrasion or breakdown; a high standard deviation indicates the presence of both. The relationship between mean roundness, standard deviation of roundness, skewness of roundness and mean size allows for an analysis of the size reduction processes at work on the sediment; and for a comparison between the reactions of different rocks. A model, based on actual data, is given for the evolution of roundness of limestone clasts on a beach.