The sound waves induce a surface wave in the 2d plane of the surface of the water. This surface wave reflected reflects of the side walls of the container. At

The sound waves induce a surface wave in the 2d plane of the surface of the water. This surface wave reflected reflects of the side walls of the container. At specific frequencies, the reflected waves will interfere with the generated waves in such a way as to cancel the amplitudes out completely at certain points, and double amplitudes at other points. When these points are stable, the pattern is known as a standing wave. The standing waves are the patterns shown here. Imperfections in the container, the medium, and the way the sound source is transmitted to the medium make the patterns imperfect. If they were perfected, they would have a more symmetric, kalaidescopic appearance: https://www.google.com/search?q=kaleidoscope&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjlnI_0ho_OAhUFyT4KHYojBIoQ_AUICCgB&biw=1323&bih=880 https://www.google.com/search?q=kaleidoscope&source=lnms&tbm...