Becky Oskin, OurAmazingPlanet Staff Writer

Old Faithful's underground plumbing looks more like a bagpipe than a flute, a new study of the Yellowstone National Park geyser finds.

A big chamber sits about 50 feet (15 meters) underground, located southwest of Old Faithful, researchers report in a study published online March 30 in the journal Geophysical Research Letters. The exact size can't be determined, but they estimate the egg-shaped void is at least 50 feet (15 m) tall and 60 feet (18 m) wide. The cavern connects to a pipe angled about 24 degrees that feeds Old Faithful's maw.

Tiny tremors extracted from seismic records collected in the 1990s revealed the shape of the cavern and geyser conduit. Popping gas bubbles create the tremors. Not only do the tremors map the shape of underground spaces, they can also track water. For the first time, scientists have a clear view of how Old Faithful works underground.

"We're able to locate with one- to two-meter precision the place where the boiling occurs," said Jean Vandemeulebrouck, a geophysicist at the University of Savoie in France. "We can see the water rising in the conduit."