Many bemoan the shortage of helium for the lab, but for geologists, its true value is in the ground.
The ancient mariner and his ill-fated shipmates in Samuel Taylor Coleridge’s epic poem were tormented by the sight of “Water, water, every where/Nor any drop to drink”. That sentiment is likely to be shared by physicists and other researchers who have struggled in recent years to find cheap helium for their studies, equipment and experiments, when they read that massive quantities of the gas have been found escaping from the well-trodden and turbulent ground of Yellowstone National Park in Wyoming.
And we do mean massive amounts. Perhaps one billion years’ worth of stored helium is fizzing up from Earth’s crust beneath Yellowstone, only to disappear into thin air.
Meanwhile, the US Geological Survey (USGS) reported last month that helium prices reached an 18-year high in the 12 months to September 2013 — around the same time that the US Congress voted to postpone closure of the nation’s strategic helium reserve. In doing so, Congress overruled an older law requiring that the United States sell off supplies of the gas that it has hoarded since the 1920s — an economic albatross around the neck of the laws of supply and demand that many blame for the current price volatility (see Naturehttp://doi.org/rkc;2013).
The United States is by some distance the world’s largest helium supplier. Yet there is unlikely to be a sensible and affordable way to tap the gas flooding into the atmosphere at Yellowstone. So, the waste is inevitable. Instead of bemoaning it, admire the science it brings. As useful as extracted, processed and packaged helium is to researchers in the lab, the true value of this noble gas for Earth scientists lies in the ground. Subterranean helium is a crucial geophysical tracer and one used, for example, to date groundwater and to track the rise of the continents.
Around the world, geysers and hot springs bubble this telltale helium to the surface. The ratios of helium isotopes in such escapes provide clues about the characteristics of volcanic activity in the crust and mantle. At Yellowstone, these isotopes help geologists to make sense of a particular super-volcano feature called the Yellowstone hotspot.
Much of the helium emitted at Yellowstone is helium-4, an isotope produced by radioactive decay of elements such as uranium and thorium in the crust. (The other common isotope, helium-3, is a primordial relic of the formation of the planet.)
On page 355 of this issue, Jacob Lowenstern and his colleagues at the USGS show that the helium-4 emission rates from Yellowstone exceed any conceivable rate of generation within the crust. Instead, it must have accumulated in the crust underneath Yellowstone for hundreds of millions of years, until the geological carnage of the Yellowstone hotspot allowed it to escape. Perhaps one billion years’ worth has been liberated over the past two million years. And still it comes. As Coleridge said, “The very deep did rot: O Christ!/That ever this should be!”
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Helium high. Nature 506, 266 (2014). https://doi.org/10.1038/506266a