Dispersion

The speed of gravity waves on deep water is wavelength dependent.

... where g is the acceleration due to gravity and l is the wavelength. Velocity is independent of the depth, density, and surface tension of the water. Longer wavelengths travel faster, as seen in this photograph of ripples spreading from a single disturbance.

The effect is called dispersion. Dispersion creates the colors of a rainbow, adds 'fire' to a sparkling diamond, and broadens pulses on optical fibers.

> More