What happens to the top of a wave as it breaks?

When a wave breaks, the top of the wave, known as the crest, maintains its forward velocity as the wave moves toward the shore. As the water beneath it becomes shallower, the base of the wave slows down due to friction with the ocean floor. This difference in speed causes the crest to rise higher and eventually become unstable, leading it to fall forward in a spilling, plunging, or collapsing motion.

This behavior is a fundamental aspect of wave mechanics; as waves approach the shore and interact with the seabed, they change shape and break. The wave does not completely disappear, nor does it continuously rise without eventual collapse. While a new wave might form as part of a series of waves, the specific action referenced in the context is the motion of the crest maintaining its forward momentum before falling over.