Large amount of helium is escaping from rocks beneath the Yellowstone National Park, researchers have found.

According to researchers at the U.S. Geological Survey's Yellowstone Volcano Observatory, the gas comes from a vast store of helium trapped in the Earth's crust for millions of years.

"The amount of crustal helium coming out is way more than anyone would have expected," said Jacob Lowenstern, lead study author and scientist-in-charge at the U.S. Geological Survey's Yellowstone Volcano Observatory, according to Livescience.

Yellowstone's hydrothermal vents release a mixture of gases including carbon dioxide, methane, neon, argon and helium.

Helium can be released by hydrothermal activity. But, the latest study shows that the amount being released now is from trapped helium beneath Yellowstone.

Yellowstone gysers are present within the remains of a supervolcano that erupted over 2.1 million years ago. The source of the volcano was a blob of molten rock rising from the mantle to the surface, Livescience reported.

According to the scientists, the supervolcano was stable for 2 billion years before its eruption, giving the rocks plenty of time to accumulate helium.

The stability in the region meant that this accumulated helium (formed due to decay of radioactive elements such as uranium and thorium) had nowhere to go.

It's only when the blob of magma heated the crust that the helium found a way out of the crust.

Lowenstern said that the entire process is comparable to a faucet. "It was like a spigot that was turned off for a really long time, not allowing the helium to migrate through the crust, and when the hotspot came to Yellowstone, it turned the spigot back on," he told Livescience.

Tracking Helium

Helium on earth can be found in two main forms; helium 4 (two protons and two neutrons- can be produced by radioactive decay of heavy elements) and helium 3 (two protons and one neutron- present since the planet's formation).

The ratio between helium 3 and helium 4 can help researchers determine the source of the helium, Smithsonian reported.

According to Livescience, helium from Yellowstone has high levels of helium-3. However, researchers also found presence of helium-4. It's a little bit surprising," Lowenstern told Live Science's Our Amazing Planet. "Not only is there this really impressive mantle source, but there's also this crustal source, too. It was definitely exciting to see this old signature."

The study is published in the journal Nature.

The helium being released at Yellowstone is larger than expected, but not large enough for the park to start selling balloons or for vistors to get squeaky voice, Smithsonian reported.