Yellowstone is North America’s largest volcanic field, produced by a “hotspot” – a gigantic plume of hot and molten rock – that begins at least 400 miles beneath Earth’s surface and rises to 30 miles underground, where it widens to about 300 miles across. There, blobs of magma or molten rock occasionally break off from the top of the plume, and rise farther, resupplying the magma chamber beneath the Yellowstone caldera.
The Yellowstone “supervolcano” rose at a record rate since mid-2004, likely because a Los Angeles-sized, pancake-shaped blob of molten rock was injected 6 miles beneath the slumbering giant, University of Utah scientists report in the journal Science.
The upward movement of the Yellowstone caldera floor – almost 3 inches (7 centimeters) per year for the past three years – is more than three times greater than ever observed since such measurements began in 1923, writes lead author Robert B. Smith, professor of geophysics at the University of Utah, geophysics postdoctoral associate Wu-Lung Chang and colleagues.
“There is no evidence of an imminent volcanic eruption or hydrothermal explosion. That’s the bottom line,” says Smith. “A lot of calderas [giant volcanic craters] worldwide go up and down over decades without erupting.
“Our best evidence is that the crustal magma chamber is filling with molten rock,” Smith says. “But we have no idea how long this process goes on before there either is an eruption or the inflow of molten rock stops and the caldera deflates again,” he adds.
The magma chamber beneath Yellowstone National Park is a not a chamber of molten rock, but a sponge-like body with molten rock between areas of hot, solid rock.
Chang, the study’s first author, says: “To say if there will be a magma [molten rock] eruption or hydrothermal [hot water] eruption, we need more independent data.”
Calderas such as Yellowstone, California’s Long Valley (site of the Mammoth Lakes ski area) and Italy’s Campi Flegrei (near Naples) huff upward and puff downward repeatedly for decades to tens of thousands of years without catastrophic eruptions.
Smith and Chang conducted the study with University of Utah geophysics doctoral students Jamie M. Farrell and Christine Puskas, and with geophysicist Charles Wicks, of the U.S. Geological Survey in Menlo Park, Calif.
Previous research indicates the magma chamber begins about 5 miles beneath Yellowstone and extends down to a depth of at least 10 miles. Its heat powers Yellowstone’s geysers and hot springs – the world’s largest hydrothermal field.
As Earth’s crust moved southwest over the Yellowstone hotspot during the past 16.5 million years, it produced more than 140 cataclysmic explosions known as caldera eruptions, the largest but rarest volcanic eruptions known. Remnants of ancient calderas reveal the eruptions began at the Oregon-Idaho-Nevada border some 16.5 million years ago, then moved progressively northeast across what is now the Snake River Plain.
- University of Utah