"This black, square-shaped platform is being vibrated by an amplified wave generator whose frequency is being gradually increased while someone pours salt on it to reveal the standing waves generated at the resonant frequency (the first pattern) or a harmonic of the resonant frequency (all the other patterns) of the black square. Each time the visible pattern changes, the wave generator "finds" another harmonic of the square's resonant frequency.
The salt makes these standing waves visible sine the salt is vibrated away from the areas of the platform which are moving, and subsequently rest in the areas which not moving. These areas in the platform which are not moving are where the standing wave nodes reside.
While the study of these waves is called cymatics (http://en.wikipedia.org/w iki/Cymatics), the patterns themselves are caused by the standing waves. These patterns exist everywhere, we just normally don't get to witness them."