Ocean Waves and Seafloor Interaction

In the vast open ocean, waves are known as deep water waves, and their speed is determined by their wavelength. But what happens when these waves venture closer to shore, into shallower waters? Here, their behavior changes dramatically due to their interaction with the sea floor.

As waves near the shore, they eventually reach a point where the water depth is half their wavelength, known as the wave base. It’s here that the sea floor starts influencing the wave. The friction between the wave and the bottom slows the wave down, causing the waves behind to catch up, reducing their wavelength. However, the energy remains constant, leading to an increase in wave height.

When the wave height becomes more than 1/7th of the wavelength, the wave turns unstable and forms a breaker. You’ve probably seen these as the curling waves at the beach.

The reason they curl forward is that the bottom of the wave, touching the sea floor first, slows down, while the top continues at its original speed, leading to the characteristic breaker shape.

There are three types of breakers:

Another interesting phenomenon is wave refraction. This occurs when waves approach the shore at an angle. The part of the wave closer to the shore, touching the bottom first, slows down, causing the wave to bend and align more parallel to the shoreline. This refraction creates larger waves off points and headlands and smaller, calmer waves in bays. This difference also explains the erosion at points and sediment deposition in bays.

What's The point_science (1)

Waves change behavior near the shore due to sea floor interaction. Friction slows the wave down, increasing its height and reducing its wavelength until it becomes unstable and forms a breaker. Three types of breakers exist. Wave refraction bends waves that approach the shore at an angle, creating larger waves off points and smaller waves in bays.

UP NEXT: Moon & Sun in Tides & Tidal Patterns

[CC BY-NC-SA 4.0] UNLESS OTHERWISE NOTED | IMAGES: LICENSED AND USED ACCORDING TO TERMS OF SUBSCRIPTION - INTENDED ONLY FOR USE WITHIN THE LESSON. NOAA video used with permission from site.