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November 2008

Yellowstone rising

Digital elevation map of Yellowstone and Grand Teton national parks overlaid with elevation change data (colours) from Global Positioning System receivers and satellite measurements. The red arrows pointing up represent uplift of the caldera.

The supervolcano is inflating at record rate, reports Ted Nield

The Yellowstone “supervolcano” rose at a record rate since mid-2004, probably because a Los Angeles-sized, pancake-shaped blob of molten rock was injected 10km beneath the slumbering giant, University of Utah scientists report in the journal Science.

“There is no evidence of an imminent volcanic eruption or hydrothermal explosion. That’s the bottom line” says seismologist Robert B Smith, lead author of the study and professor of geophysics at the University of Utah. “A lot of calderas worldwide go up and down over decades without erupting.”

The upward movement of the Yellowstone caldera floor – almost 7 centimetres per year for the past three years – is more than three times greater than ever observed since such measurements began in 1923, says the study in the Nov. 9 issue of Science by Smith, geophysics postdoctoral associate Wu-Lung Chang and colleagues.

“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.

Yellowstone is North America’s largest volcanic field, produced by a “hotspot” – a gigantic plume of hot and molten rock – that begins at least 650km beneath Earth’s surface and rises to 50km underground, where it widens to about 480km 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.

Previous research indicates the magma chamber begins about 8km beneath Yellowstone and extends down to a depth of at least 16km. Its heat powers Yellowstone’s geysers and hot springs – the world’s largest hydrothermal field.


Trigger events

Ratnal Earthquake.

Big earthquakes spark off jolts worldwide, even on the opposite side of the Earth, reports Dwain Eldred

Until 1992, when California’s magnitude-7.3 Landers earthquake set off small jolts as far away as Yellowstone National Park, scientists did not believe large earthquakes sparked smaller tremors at distant locations. Now, a definitive study shows large earthquakes routinely trigger smaller jolts worldwide, including on the opposite side of the planet and in areas not prone to quakes.

“Previously it was thought seismically active regions or geothermal areas were most vulnerable to large earthquake triggers,” says Kris Pankow, a seismologist at the University of Utah Seismograph Stations and a co-author of the study.

But Pankow and colleagues analysed 15 major earthquakes stronger than magnitude 7.0 since 1992, and found that at least 12 of them triggered small quakes hundreds and even thousands of miles away, according to the findings published in the online version of Nature Geoscience.

“We conclude that dynamic triggering is a ubiquitous phenomenon,” they write.