Waves primarily get taller as they approach the shore, a phenomenon driven by the changing depth of the water.
The Mechanics of Wave Height Increase Near Shore
As ocean waves travel from deep water into shallower areas, a specific interaction with the seabed causes their height to increase significantly. This process, often referred to as shoaling, is detailed in the provided reference:
- Approaching the Shore and "Touching Bottom": When waves move into shallower water, they eventually reach a point where the water depth becomes equal to half of their wavelength. At this critical depth, the wave begins to "touch bottom," meaning its motion starts to be affected by the seabed.
- Slowing Down: As a direct consequence of interacting with the seafloor, the wave's speed begins to decrease. This friction and energy dissipation cause the wave to slow down.
- Wavelength Decreases: Simultaneously with the decrease in speed, the wave's wavelength—the horizontal distance between two consecutive crests—also decreases. This compression of the wave's energy into a shorter horizontal distance is crucial.
- Wave Height Increases: The combination of the wave slowing down and its wavelength decreasing forces the wave's energy to be concentrated into a smaller volume. This compression leads to a notable increase in the wave height.
- Breaking Point: This process of increasing height continues until the wave becomes unstable and breaks, forming surf.
As Steven Earle describes in “Physical Geology,” waves approach shore and "touch bottom" when the depth equals half of the wavelength, causing the wave to slow down. As it slows, the wavelength decreases and the wave height increases, until the wave breaks.
