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John Hollenhorst ReportingImagine a pristine mountain stream that turns on and off every few minutes, all by itself. Believe it or not, there is such a Mystery River not far from here, one of only two in the entire world.
Now, University of Utah scientists have new evidence that may explain how the phenomenon works.
It's not a big river. It's an icy mountain stream. But a few minutes later, it's gone. And a few minutes after that, it's back.
Gerald Vanbrunt, Arkansas Tourist: "This is just as good as Old Faithful."
But it's not a geyser; it's fed by a cold-water spring. In fall and winter it has a natural cycle, about 20 minutes on, 20 minutes off.
The only other spring like it in the world is in France. It's a point of pride in nearby Afton, Wyoming.
Al Hale, Afton, Wyo. Resident: "Well the folklore is that the Indians were the first ones to see this phenomenon."
Just before it erupts, the spring emits a deep gurgling noise. A rising puddle quickly becomes a surprisingly vigorous roaring creek.
Kip Solomon, University of Utah Hydrologist: "Well, everything about this spring is somewhat surprising. It's an extremely unusual occurrence."
The town of Afton built a structure to protect their water supply. It's very cold, very pure, and it tastes good. It's won national awards.
Rulon Gardner, Olympic Gold Medalist: "Of course! You know, Star Valley water. It's the best in the world."
Olympic gold medalist Rulon Gardner's great-great grand-dad is credited with the discovery.
Rulon Gardner, Olympic Gold Medalist: "He was up there logging. He went up and found a nice little place to get some fresh water. It was intermittent. It went, and stopped. So it was pretty amazing."
In late summer, scientists collected water samples. They're exploring an old theory involving a mysterious underground chamber.
Prof. Kip Solomon: "We can't think of another explanation at the moment."
Here's the theory: As groundwater flows continuously into a cavern, it fills a narrow tube that leads out. As it pours over the high point of the tube, it creates a siphon effect, sucking water out of the chamber. Eventually air rushes in and breaks the siphon.
Gerald Vanbrunt, Arkansas Tourist: "It's kind of like a toilet flushing. All the water goes out, it fills back up, and goes back out."
The spring water's gas content has now been tested at the University of Utah. The data strongly suggests the water was exposed to air underground; strong support for the siphon theory.
Prof. Kip Solomon: "Yeah, I think that we're a step closer to the answer."
Someday, science may have a definitive answer. For now, we can just enjoy the natural wonder of an on-again, off-again, mystery river.
The intermittent spring is at the end of a half-mile hike, in a canyon straight east of Afton, Wyoming.