Catching up from behind

Waves grow taller

When the wave in front slows down, the wave behind catches up and the crests get closer together. The 156 m gap out at sea shrinks to 59 m just before breaking. The wave carries almost the same energy, but now it is squeezed into less space. So the wave grows: a 2.5 m wave becomes about 2.9 m tall.

Why?When the car in front slows down, the cars behind catch up and the gaps between them shrink. Waves do the same. The difference is that the squeezed energy makes the wave taller.

Learn moreWaves growing taller as the water gets shallower is called shoaling. The numbers here come from a formula that assumes small waves. Real waves get even more peaked and taller just before they break.

Height just before breaking

2.9 m

Out at sea

2.5 m high · 156 m apart

3.8 m deep

2.9 m high · 59 m apart

calculated from the textbook equations for water waves (linear wave theory)