A rhythmic spring is a water spring from which the flow of water either varies or starts and stops entirely, over a fairly regular time-scale of minutes or hours. The “Intermittent Spring” located in Swift Creek canyon in Star Valley, near Afton, Wyoming is the largest rhythmic spring in the world. The theory is that as groundwater flows continuously into a cavern, it fills a narrow tube that leads out. As the cavern overflows it creates a siphoning effect and when that happens the hydraulic effect pulls the water out of that cavern and creates a river which runs for about 15 minutes. Eventually this siphon is broken once air reaches the pipe and it breaks off. Then the cavern fills again with water and it starts the process all over again.