A standing wave is made by sending a wave group down the tank against a fixed wall. The reflected wave will superimpose upon the incident waves doubling the amplitude. As the wave maker imparts more energy in to the system, the amplitude increases. The waves are sustained by gravity and hydrostatic force and dissipated by fluid viscosity (the frictional forces against the wall are negligible). The video has been edited as the clopotis and seiche that occur last over a half hour and are eventually killed with the wave maker acting as an absorber, as it tries to produce waves offset by one half period of the waves hitting it.