This week, a survey will begin to map the underground hydrothermal features of Yellowstone National Park for the first time. 
 
 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 data will be able to tell the scientists if they are flying over solid earth, “rotten” sulfuric rock, or water. Carol Finn, one of the scientists on the surveying team, said she has been looking forward to this for ten years. 
 
 “This is really kind of a last frontier if you will, in Yellowstone, of being able to look at a large part that’s underground that people that people have not looked at,” said Finn. “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. 
 
 “There’s just a lot we don’t know and this survey is really exciting because it’s going to be the first view of a large portion of the groundwater system, of the water underground that feeds all of these thermal features,” said Finn. 
 
 The survey will also provide information that could help the park in the future by locating unstable ground. The researchers will fly the helicopter along the Mammoth-Norris corridor and take at least four weeks to complete. ||||| BILLINGS, Mont. (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. 
 
 Throughout November the research team will conduct flights over the park using a giant, hoop-shaped electromagnetic system suspended from a helicopter. The device acts like an X-ray to determine where and how hot water flows beneath the surface. 
 
 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. 
 
 One such explosion, or possibly multiple explosions, that occurred roughly 13,800 years ago left a crater that measures 1-1/2 miles (2.6 km) across beneath at the bottom of Yellowstone Lake. It's believed to be the largest such crater in the world. 
 
 Similar to the regular eruptions of Old Faithful, hydrothermal explosions occur when huge pockets of boiling water beneath the ground experience a sudden drop in pressure, causing the water to convert to steam and explode violently to the surface. 
 
 Similar work elsewhere in the U.S. has helped reveal hazards from volcanoes. 
 
 "Nobody knows anything about the flow paths" for the hot water that erupts from Yellowstone's geysers, Finn said. "Does it travel down and back up? Does it travel laterally?" 
 
 The electromagnetic system was developed in Denmark to map out groundwater supplies in Denmark. It's able to discern between water and rocks to a depth of about 1,500 feet beneath the surface. 
 
 In Yellowstone, a better understanding of the hydrothermal plumbing could help administrators plot out future development so tourists can enjoy the park's features without damaging them or being put into harm's way. 
 
 The study is a collaboration between the U.S.G.S., Yellowstone National Park, the University of Wyoming and Denmark's Aarhus University.
– 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.)