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Beach cusps
Beach cusps are shoreline formations made up of various grades of sediment in an arc pattern. The horns are made up of coarser materials and the embayment contains all the finer grain sediment. They can be found all over the world and are most noticeable on shorelines with coarser sediment such as pebble beaches. However, they can occur with sediment of any size. They nearly always occur in a regular pattern with cusps of equal size and spacing appearing along stretches of the shoreline. These cusps are most often a few metres long. However, they may reach across. Although the origin of beach cusps has yet to be proven, once cusps have been created they are a self-sustaining formation. This is because when an oncoming wave hits the horn of a beach cusp, it is split and forced into two directions. The crashing of the wave into the cusps slows its velocity, causing coarser sediment to fall out of suspension and be deposited on the horns. The waves then flow along the embayments (picking up finer sediment) and run into one another in the middle. After this collision these waves attempt to flow back out to sea where they are met by incoming waves. Therefore, once the cusp is established, coarser sediment is constantly being deposited on the horn and finer sediment is being eroded away from the embayments.〔Easterbrook, Don J. Surface Processes and Landforms. Second Edition. Prentice Hall. 1999. 447-448 pp.〕 This process causes the horns and embayments to at least maintain their size, if not grow larger.
==Formation==
There are a number of theories as to why beach cusps are formed but currently, there are only two explanations with any real credibility.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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