from: https://yoursportspot.com/post-87169553/28/?dai=5WEx178DUwzeZul30R7NlU&fbclid=IwAR3dqJHLzuQrWM6Q08J8Usqbfs2xn2TDHne3w3LBNVyWQT3ueQhSUtaWd_U
Square Waves
The idea of a square wave seems like a geometric absurdity. When two wave systems run into each other, however, a “cross sea” is created. As you can see in the picture below, the phenomenon is aptly named because of the patchwork pattern formed in the waves.
Although the cross sea makes for a good picture, it can be extremely dangerous for swimmers, surfers, and even passing ships. Beneath these waves is an insanely strong current which can pull you out to sea.
The Isle of Rhe in France is known for this phenomenon but it can also occur in other places, such as New Zealand.