The giant magma blob beneath Yellowstone National Park unleashed tons of ancient helium gas when it torched North America, according to a new study.
“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. The findings appear in today’s (Feb. 19) issue of the journal Nature.
Yellowstone National Park’s famous geysers burble within the remains of a supervolcano that first exploded 2.1 million years ago. Both the volcano and the geysers owe their existence to a hotspot, a massive plume of molten rock rising from within Earth’s mantle toward the surface. [Infographic: The Geology of Yellowstone]
However, before western North America trundled over the hotspot, Yellowstone’s future birthplace went undisturbed for more than 2 billion years, the study authors think. This gave the continental rocks plenty of time to build up big helium-gas stores via the decay of radioactive elements in the crust. (Most helium created on Earth comes from uranium and thorium.) The helium was probably trapped both in rocks and in fluids such as groundwater.
Because all was quiet in this corner where the West meets the Plains, no tectonic grinding freed the helium via fractures such as faults. Only when the hotspot drilled through the crust a couple of million years ago could the helium finally escape. The rising magma heated and cracked the crust, releasing the gas, and provided a path to the surface via churning fluids and molten rock.
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