The Linear Dispersive Focusing Mechanism

The ocean consists of many, many waves and they travel in not random, but in lots of directions. And at some point in time, quite a few waves come together and they build up. One mechanism is to do with nonlinear effects where these waves that come together just don't add up linearly. So it's not one meter plus one meter giving two meters, but it's onemeter plus one meter all of a sudden giving three meters.