Waves are caused by wind blowing on the ocean surface. Stronger winds cause larger waves. Variations in wind speed and duration determine the size and frequency of waves. The horizontal length of the wave is established by the horizontal distance between its two crests and the vertical length is established by the vertical distance between the crests. Large waves can also be created by undersea seismic activity.
Waves are the forward motion of water. Waves reach down to the ocean floor, and only a portion of a wave is visible on the surface. Waves are initially formed out in the open ocean, beginning as generally vertical in shape.
As the wave travels toward the shore, the lower section drags the bottom of the ocean floor. The surface section of the wave moves faster than the submerged portion. As the wave reaches the more shallow water levels near the shore, the drag of the seafloor increases, slowing the underwater section of the wave even more, causing the wave to tilt forward. The rolling wave eventually tilts far enough forward that it curls over, creating the effect that is called the “breaking” or “crashing” of waves. The area between the shore and the point where the waves break is known as the “surf zone.”