Rhythmic Springs
A rhythmic spring (also: ebb and flow spring, periodic spring, intermittent spring) is a cold 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. Compared to continuously-flowing springs, rhythmic springs are uncommon, with the number worldwide estimated in 1991 to be around one hundred.
Although the cause of the periodicity in flow is not known for certain, the most accepted theory (first postulated in the early 18th century) is that as groundwater flows continuously into a cavern, it fills a narrow tube that leads upwards from near the base of the cavern, then downwards to the spring. As the water level reaches the high point of the tube, it creates a siphon effect, sucking water out of the chamber. Eventually air rushes into the tube and breaks the siphon, stopping the flow if there is no other source feeding the spring, or reducing the flow if there is a continuous flow from another non-siphon source.
Source
Swift Creek flowing out of the Intermittent Spring in Wyoming.
Source / Image Courtesy
Rhythmic springs are those springs that exhibit tidal characteristics. In other words, the water level of these springs rises and falls over a fairly regular time period. Sometimes the spring would stop flowing completely and start again after a couple of hours or minutes. The cause of this periodicity is not truly understood.