Yellowstone eruption unlikely

YELLOWSTONE NATIONAL PARK, Wyo. — Geothermal activity is increasing in a Yellowstone National Park geyser basin and the bottom of Yellowstone Lake is bulging, but scientists say there is no impending major eruption.

Searing ground temperatures, bursts of steam and flows of hot water prompted park officials to close about half the trails in Norris Geyser Basin this summer, and the increased thermal activity has led to concern among some visitors about the potential for an eruption.

"This is just part of the change that goes on in Yellowstone," park geologist Hank Heasler said. "I won't say it's normal, because we don't know what 'normal' is."

But scientists say there is no evidence that Yellowstone is poised for a powerful eruption, such as the one that rocked the region 600,000 years ago.

If the park were ready to blow its top, there would be several signs that magma was moving toward the surface, and earthquakes would be more frequent and stronger. The ground, while often rising and falling in Yellowstone, would most likely gradually rise and the chemistry of many geysers would change.

All of that activity is constantly monitored by scientists with the Yellowstone Volcanic Observatory, a long-running study of the park's underground systems.

If the park were poised for a major eruption, the signs wouldn't be subtle, Heasler said.

"I doubt you'd need seismographs to know that changes were happening in Yellowstone," he said.

Early signs of an impending outburst would be similar to the 1980 eruption of Mount St. Helens in Washington state. Scientists knew something big was brewing months ahead of time although they couldn't predict exactly how big or when the eruption was coming.

The current geologic activity in Yellowstone appears to be much closer to the surface than would be exhibited by magma flows. At such shallow depths, water heated by the earth is driving the changes.

"We're not searching for magmatic fluids," said Bob Smith, a geologist at the University of Utah who has studied the park for three decades. "We think this is a very shallow system."

Norris is the most dynamic of the park's geyser basins and Jacob Lowenstern, a researcher at the U.S. Geological Survey in Menlo Park, Calif., said it always experiences increased activity in summer.

But this year is exceptional, with a new mud pot welling up, 200-degree temperatures on the ground and geysers that haven't erupted in years spouting off.

And unlike years past, dramatic improvements in equipment are allowing scientists to peek deeper and more precisely record changes in the upper plumbing. They are using precision seismometers and satellite-mapping systems to record the changes.

"Let's say we're doctors and Norris Geyser Basin is our patient," Heaslier said. "Before, we had the ability to take its pulse and temperature. Now we have a stethoscope and an X-ray machine, and we can look inside."