Origin and development of beach cusps at Monterey Bay, California

Abstract

Beach cusps were observed daily on Del Monte Beach and measurements obtained so that a quantitative description of the parameters which affect formation and size of cusps could be determined. In addition a theory of cusp formation was formulated and an insight obtained into the factors which influence the shape and size of cusps throughout their lifetime. Finally, the events leading to cusp destruction were examined. It was determined that beach cusps are depositional in nature, forming most easily in coarse, loose sediment. Cusp development commences at a rise or area of accretion on the beach. A series of beach cusps forms sequentially rather than simultaneously. The width of beach cusps are a function of wave height; the larger waves producing wider cusp spacing. Uniform spacing of cusps in a series can be attributed to the same size waves striking the beach during the formation period of the cusps. Once formed, cusps are stable and tend to maintain their dimensions unless a large change in wave or beach condition occurs.