The sound of erosion at Rialto Beach, Washington 

Gravels predominate on Rialto Beach on Washington's Olympic Peninsula. This video starts with a receding wave. Afterward another wave comes in. As that one recedes, listen closely, and you may be able to hear the subtle sounds of rocks clacking together. I observed rocks being rolled by wave action to produce that sound. Given enough time, the action of waves rolling rocks and cracking them together will eventually break down the beach's gravels into smaller and smaller particles, e.g. sands.