Yellowstone National Park has long been known as a gassy place, and its reputation as such just got more firmly established. That helium emanates from the ground in the park is an established fact, Smithsonian Magazine explains, but when researchers dug into the makeup of that helium, what they found was a surprise. Helium generally takes one of two forms, helium-3 or helium-4; in a new study in Nature, US Geological Survey researchers reveal that the emissions of helium-4 "exceed (by orders of magnitude) any conceivable rate of generation within the crust." So that helium is pretty ancient, having "accumulated for (at least) many hundreds of millions of years" in the rocks beneath the park.
Researchers found that the park's steam vents and hot springs are releasing hundreds or even thousands of times more helium-4 than we thought—at 60 tons a year, enough to fill a Goodyear blimp weekly, the LA Times reports. In geological terms, the helium has been building for ages, and the release is a "sudden" one that started a mere 2 million years ago, having been spurred by heat from a volcano deep under the park. "You have these old crustal rocks just sitting around" for ages, one researcher explains, "and then suddenly somebody puts the heat on under them and they start giving up all their long-held secrets."