Square waves: where they come from and why they are dangerous

In some places on our planet, you can see waves that are not familiar to everyone. They will not roll on the shore in parallel, as everyone is used to it. From the outside, it seems that such waves roll on the shore itself and on top of each other in a perfectly smooth checker. This phenomenon is called square waves. The angle between such waves can be very different and sometimes reaches even 90 degrees.

You can see similar waves on the island of Re, which is located near the Western part of France, as well as on the Azores, the beaches of tell Aviv and some other coastal regions.

Cross-wave sources can be very diverse. For example, waves due to the sea current are directed in one direction, and at the same time due to the wind-in the other. Waves can collide with each other as a result of two different storms. Sometimes the wind direction changes dramatically, which affects the direction of the waves and they roll over the previously formed ones. This phenomenon is very well explained by the special Kadomtsev-Petviashvili equation.

In shallow water, the cross surf will not be particularly high, but it is very dangerous to swim in such waves. Away from the shore, cross waves are high enough to flood even yachts and small vessels. During the pitching, they will turn perpendicular to the waves, but you will not be able to swim this way and there is a risk that another wave will either flood or capsize the ship.