Yellowstone Is Rising on Swollen "Supervolcano"

Richard A. Lovett
for National Geographic News
November 8, 2007
Yellowstone National Park is rising. Its central region, called the Yellowstone caldera, has been moving upward since mid-2004 at a rate of up to three inches (seven centimeters) a year—more than three times faster than has ever been measured.

The surface is inflating like a bellows due to an infusion of magma about 6 miles (10 kilometers) underground, according to a new study published in tomorrow's issue of the journal Science.

But that doesn't mean Yellowstone is about to go the way of Mount St. Helens.

"There's no evidence of an imminent eruption or hydrothermal explosion," said Robert Smith, a geophysics professor at the University of Utah who co-authored the study.

"Supervolcano" Under Yellowstone

Yellowstone is situated on a giant, geologically active feature known as a supervolcano.

"It's hundreds of times bigger than Mount St. Helens," Smith said, referring to the active volcano in Washington State.

(Read related story: "Supervolcano Raises Yellowstone, Fuels Geysers, Study Says" [March 1, 2006].)

Much of the park sits in a caldera, or crater, some 40 miles (70 kilometers) across, which formed when the cone of the massive volcano collapsed in a titanic eruption 640,000 years ago.

The supervolcano has produced three similarly large blasts in the past two million years, with 30 smaller eruptions since the caldera formed.

The volcano's most recent flare-up was 70,000 years ago, and volcanic heat continues to fuel the park's famous geysers and hot springs.

(See photos of Yellowstone National Park.)

The land is rising because magma and hydrothermal fluids are migrating into the volcano's underground chambers, Smith explained.

"It's really kind of a sponge, where you have interlaced open spaces with magma and solid rock between. Only 10 percent [of the chambers are] actually made up of molten rock."

The current uplift was detected by global positioning system stations and radar instruments on an orbiting satellite.

Kenneth Pierce of the U.S. Geological Survey in Bozeman, Montana, has studied ancient water levels in Lake Yellowstone to track elevation changes in the underlying portions of the caldera (see a map of Yellowstone National Park).

He said the newly detected upswell is part of a natural cycle that is common to calderas.

"Since … about 14,000 years ago, the Yellowstone caldera has inflated and deflated about six to eight times without a volcanic eruption," he said.

Smith agreed. "Calderas go up and down," he said. "We use the term 'restless' to describe these systems."

But, he added, "occasionally they burp."

When the volcano might "burp" next isn't clear, because highly accurate, modern instruments have only been around for a few years, Smith explained.

"It's hard to predict what's going to happen in the future when you have such a short record," Smith said.

Hot Spot

One thing that is certain is that the Yellowstone volcano isn't dead.

Many scientists believe the volcano is produced by a "hot spot" in the Earth's mantle, a plume of hot rock rising from hundreds of miles below.

Since the hot spot first rose 16 million years ago, it has produced at least 140 eruptions throughout the northwestern United States, Smith said.

To gauge any future volcanic activity, the park is continuously monitored by instruments associated with the Yellowstone Volcano Observatory, which is jointly administered by the University of Utah, the U.S. Geological Survey, and Yellowstone National Park, he added.

"These provide information of public safety, daily [and] in real time."

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