Waves can carve solid rock because water is one of the most common causes of erosion, the natural process of change taking place on the Earth’s surface all the time. Erosion began when Earth began and it will continue as long as Earth exists despite man’s puny efforts to control nature.
Erosion requires the movement of forces, primarily water and wind, and the accompanying process of wearing down rocks, soil, and minerals by friction so that small, possibly microscopic pieces are shed into the water. The creation of such matter and its movement is a process called sedimentation, quite literally making sandpaper out of water. Without both moving water and sediment, erosion would be greatly reduced, but moving water always causes erosion regardless of the kind of material against which it moves. It’s all a matter of time.
Other factors are involved in the changing of the Earth’s surface such as glaciers and wind which can also actually change surface features of the land both around and under water, but it is flowing water that causes the erosion and carving of rock where the land slopes at least two percent. Rocky shorelines all over the Earth, around the oceans, rivers, lakes, ponds, and streams demonstrate the fact that sloping shores of rock can actually deepen over time from the action of waves or flowing water. No more dramatic demonstration of the power of water to carve stone exists than Grand Canyon, a monumental chasm created by the flow of the Colorado River over millennia. The river continues to carve its way through a variety of stones and soils that make up the shoreline, each type contributing its share of grinding materials so that the erosion can continue so long as the river runs.
Erosion is most easily demonstrated in softer materials such as soil where the effect of too much water flowing from a downspout can gouge out first a depression then a trench from the soil under it as the water seeks to run downhill. This erosive process doesn’t take long, not more than a day or two in some soils, and requires little or no sediment to occur. Erosion of granite, however, takes centuries because it is generally a dense rock that does not break down easily or quickly.
Sometimes forces such as ice along a shore line will assist in the process of carving the stone by freezing and thawing in the natural fissures of stone, thus allowing pieces to break off. The result can be clearly seen on a rocky lakeshore where boulders of all kinds break off into the water each winter. The process of reducing the boulders to pebbles and then to sand is probably too long to demonstrate in a person’s lifetime, but it inevitably occurs.
In addition, wind plays an important part in water’s ability to carve stone because it carries sediment and deposits it in new locations, enhancing the water’s ability to erode the rocky shore more effectively. Wind also plays a major role in the motion of waves without which a body of water cannot cause much erosion except by eventually dissolving rock. A farmer's pond deep in the shelter of surrounding hills does not erode quickly because the water is sheltered from wind and seldom moves.