A wave begins as the wind ruffles the If it n surface of the ocean. When the ocean is calm and glasslike, even the mildest breeze forms ripples, the smallest type of wave. Ripples provide surfaces for the wind to act on, which produces larger waves. Stronger winds push the nascent waves into steeper and higher hills of water. The size a wave reaches depends on the speed and strength of the wind, the length of time it takes for the wave to form, and the distance over which it blows in the open ocean known as the fetch. A long fetch accompanied by strong and steady winds can produce enormous waves.
The highest point of a wave is called the crest and the lowest point of the trough. The distance from one crest to another is known as the wavelength. Although water appears to move forward with the waves, for the most part, water particles travel in circles within the waves. The visible movement is the wave’s form and energy moving through the water, courtesy of energy provided by the wind. Wave speed also varies; on average waves travel about 20 to 50 mph. As a wave enters shallow water and nears the shore, its up-and-down movement is disrupted and it slows down. The crest grows higher and begins to surge ahead of the rest of the wave, eventually toppling over and breaking apart. The energy released by a breaking wave can be explosive. Breakers can wear down rocky coasts and also build up sandy beaches.