The magma chamber under Yellowstone volcano in Northwest US is the source of the supervolcano’s potentially cataclysmic power. Yellowstone’s magma chamber last blew its lid some 640,000 years ago, covering swathes of the North American continent in ash. The scorching chamber only sits about 3.1 miles to 9.3 miles (5km to 15km) beneath the surface, but that is not its only surprise. According to the US Geological Survey (USGS), which monitors volcanic activity at Yellowstone, the magma chamber is full of radioactive elements.
Deep beneath Yellowstone National Park, geologists have discovered deposits of the radioactive mineral zircon.
Zircon is known for its radioactive properties due to being rich in uranium and thorium – two radioactive chemical elements.
Uranium, in particular, is commonly used in nuclear weapons and is the go-to-fuel for nuclear reactors.
Thorium is a similarly unstable element, which radiates alpha particles and is more abundant in the Earth’s crust than uranium.
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This does not, however, suggest Yellowstone is a ticking nuclear time bomb of sorts.
Instead, the relatively weak radioactivity of Yellowstone’s magma holds the key to unlocking the supervolcano’s secrets.
In Yellowstone, and in other volcanic magma reservoirs, the zircon minerals have shown incredible resilience to the heat and pressures of the supervolcano system.
The resilience paired with the radioactive properties gives geologists an opportunity to study zircon minerals to determine the age of the magma chamber.
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Mark Stelten, a research geologist with the USGS, explained the process in this week’s issue of the USGS Caldera Chronicles.
The geologist wrote: “To determine the age of Yellowstone’s magma reservoir, researchers turn to a field of geology called geochronology, which is the study of the age of earth materials, like volcanic rocks and the crystals they contain and is typically based on radioactive decay.
“Magma contains radioactive atoms that are incorporated into crystals that grow from the magma.
“Over time, these radioactive atoms – the parent – will transform into another atom – the daughter – at a known rate of radioactive decay.”
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Geologists can then use this fact to their advantage by using a mass spectrometer instrument to determine the age of the minerals in which the atoms are contained.
In Yellowstone volcano, Dr Stelten said scientists have been able to analyse zircon crystals from various Yellowstone eruptions dating as far back as 160,000 years.
He said: “Results from these studies show that zircon crystals in these lavas can record as much as 150,000 years of growth in a magma chamber before eruption.
“These data suggest that the modern crystal much that underlines Yellowstone caldera may have existed in a state similar to what is imaged today since about 300,000 years ago.”
What this means, is the current magma chamber under Yellowstone National Park is at least as old as 300,000 years.
