(AP) — Scientists from the U.S. and Denmark are seeking to map out the plumbing system hidden inside the earth's crust that's responsible for the famous Old Faithful geyser and other hydrothermal features at Yellowstone National Park. The team also hopes to gain insights into the infrequent but sometimes massive hydrothermal explosions that occur in the park, said lead scientist Carol Finn with the U.S. Geological Survey. “This survey can visualize the geology and the water down to about 500 meters, so 1500 feet.” 
 
 The goal of the project is to fill in the gaps of knowledge about what causes geysers like Old Faithful and hydrothermal explosions by locating where all that heated water flows underground. The U.S. Geological Survey (USGS), in collaboration with the Aarhus University in Denmark and the University of Wyoming, will use a helicopter carrying electromagnetic technology that resembles a giant hula hoop to record tiny voltage signals.
– The mysteries of Old Faithful may soon be solved, thanks, in part, to something that looks like a giant hula hoop. American and Danish scientists have this week begun an aerial survey of Yellowstone that actually looks well into the earth, "visualizing" the geology and water as much as 1,500 feet below the surface, says Carol Finn. She's waited a decade to explore what she calls "a last frontier ... in Yellowstone," and the intention is to better map the flow of water that's feeding Old Faithful and rare but sometimes violent hydrothermal explosions. Over a four-week period, a helicopter will fly above, armed with electromagnetic technology that looks like a giant hula hoop. The AP explains it in layman's terms: "The device acts like an X-ray to determine where and how hot water flows beneath the surface." Scientists will use the data to determine whether solid earth, "rotten" sulfuric rock, or water lurks below, which could assist in identifying unstable areas, per Wyoming Public Media. But a press release frames the main quest like so: We know that the water that explodes from Yellowstone's geysers "originates as old precipitation, snow and rain that percolates down into the crust, is heated, and ultimately returns to the surface." We know that it can take as long as thousands of years for that process to run its course. What scientists are hoping to determine are the routes these waters take. "Does it travel down and back up? Does it travel laterally?" asks Finn. Right now, "nobody knows." (Archaeologists made a surprise find underneath a Mayan temple.)