how ocean waves work
The wave visible above the level of the water is in fact only part of the wave; the wave extends down through the water column to the ocean floor as well. Waves start out in the deep, open ocean as relatively vertical in shape, Presnell said. As a wave travels toward the shore, though, the bottom part of the wave drags along the ocean floor. The upper part of the wave above the water line starts to move faster than the rest of the wave. As the ocean depth decreases closer to shore, the drag on the wave's bottom becomes stronger, and the upper part of the wave begins to tilt forward.