Global reserves of helium (He)—the gas best known for making balloons float—are in short supply. But scientists recently discovered a massive underground helium source in the African nation of Tanzania. It holds more than 1.5 billion cubic meters (54 billion cubic feet) of the gas. 

Helium has important uses. It keeps medical scanners running and blasts rockets into space. The gas forms deep underground, making it difficult to locate and access. But in Tanzania, volcanic activity has moved trapped helium closer to the surface.

Scientists hope similar areas will yield similar helium deposits. “We now know what geological ingredients to look for,” says Chris Ballentine, a geologist at the University of Oxford in England.