Legion said...^ Amplitude is the same as what I was talking about, i.e. the Hawaiian system:
Number (1) in the image.
<edit>Whoops, didn't like the image much. Go to:
en.wikipedia.org/wiki/Amplitudeand look at the peak amplitude measurement</edit>
Now keep the amplitude constant and increase the interval and see how much more area is under the line per wave.
This is why waves from far distances with longer intervals have far greater power. Interval also greatly affects the speed in which waves travel.
Lets get scientific:
If you study waves, you will find that wavelength and frequency are related by an equation.
Speed of the wave = Frequency x Wavelength
Therefore, what you can see is that when the waves have greater intervals they also travel at far greater speeds. This is why islands such as Hawaii, Fiji etc with very short or nil continental shelf to slow waves down combined with very long interval swells from great distances away get very big waves.
Any more questions?