Waves curl near the shore due to a phenomenon called wave refraction. Wave refraction occurs when waves approach a coastline that has irregular shapes, such as headlands, bays, or uneven bathymetry (the underwater topography). Several factors contribute to the curling of waves near the shore:
Change in wave speed: As waves approach the shore, the part of the wave closer to the shore encounters shallower water. The decrease in water depth causes the wave to slow down since the wave base interacts with the seabed. However, the part of the wave farther from the shore is still in deeper water and continues to move at its original speed. This speed difference causes the wave to bend or refract.
Wavefront alignment: Wavefronts are imaginary lines connecting adjacent wave crests. When waves approach a coastline with an irregular shape, the shape of the coastline influences the alignment of wavefronts. As waves approach headlands or areas of shallow water, the part of the wavefront in deeper water moves faster than the part in shallower water. This difference in speed causes the wavefronts to bend, resulting in the curling or bending of the wave.
Conservation of energy: Waves carry energy, and as they approach the shore, the wave energy tends to focus on headlands and areas of shallow water. This energy concentration intensifies the wave action in these areas, leading to the curling or breaking of waves.
As waves curl or bend near the shore, the energy of the wave becomes concentrated in a smaller area, leading to an increase in wave height. This phenomenon is why waves near the shore tend to be steeper and have a curling or breaking appearance. The curling or breaking of waves is essential for processes such as wave-driven erosion, sediment transport, and the formation of surf zones, which are important features in coastal environments.