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Dec 30, 2008 12:45 pm US/Central
Yellowstone Earthquakes May Be 'Precursory' Events
Scientists Eye Unusual Swarm Of Growing Seismic Activity
CHEYENNE, Wyo. (CBS) ―
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Yellowstone remains very geologically active — and its famous geysers and hot springs are a reminder that a pool of magma still exists five to 10 miles underground. (File)
CBS
Yellowstone National Park was jostled by a host of small earthquakes for a third straight day Monday, and scientists watched closely to see whether the more than 250 tremors were a sign of something bigger to come.
Swarms of small earthquakes happen frequently in Yellowstone, but it's very unusual for so many earthquakes to happen over several days, said Robert Smith, a professor of geophysics at the University of Utah.
"They're certainly not normal," Smith said. "We haven't had earthquakes in this energy or extent in many years."
Smith directs the Yellowstone Seismic Network, which operates seismic stations around the park. He said the quakes have ranged in strength from barely detectable to one of magnitude 3.8 that happened Saturday. A magnitude 4 quake is capable of producing moderate damage.
"This is an active volcanic and tectonic area, and these are the kinds of things we have to pay attention to," Smith said. "We might be seeing something precursory.
"Could it develop into a bigger fault or something related to hydrothermal activity? We don't know. That's what we're there to do, to monitor it for public safety."
The strongest of dozens of tremors Monday was a magnitude 3.3 quake shortly after noon. All the quakes were centered beneath the northwest end of Yellowstone Lake.
A park ranger based at the north end of the lake reported feeling nine quakes over a 24-hour period over the weekend, according to park spokeswoman Stacy Vallie. No damage was reported.
"There doesn't seem to be anything to be alarmed about," Vallie said.
Smith said it's difficult to say what might be causing the tremors. He pointed out that Yellowstone is the caldera of a volcano that last erupted 70,000 years ago.
He said Yellowstone remains very geologically active — and its famous geysers and hot springs are a reminder that a pool of magma still exists five to 10 miles underground.
"That's just the surface manifestation of the enormous amount of heat that's being released through the system," he said.
"There is this huge volcano underneath Yellowstone National Park," said Greg Breining, a writer from St. Paul, Minn.
Author Greg Breining spent some time studying the geology and enjoying the natural wonders of Yellowstone before writing "Super Volcano: The Ticking Time Bomb Beneath Yellowstone National Park."
"There is this huge reservoir of magma just three or four miles beneath the surface of the park, and it is that magma -- this is still an active volcano -- that creates the geysers, the mudpots, the hot springs, all the other features for which Yellowstone is famous," said Breining.
Nearly 30 years ago, Mount St. Helens near the Washington/Oregon border erupted killing 57 people and blowing more than a 1000 feet off the top of the mountain.
"We think of mount St. Helens -- went off in 1980 -- as a big explosion, and indeed it was," said Breining. "The most recent Yellowstone explosion was a thousand times larger than Mount St. Helens."
Yellowstone has had significant earthquakes as well as minor ones in recent decades. In 1959, a magnitude 7.5 quake near Hebgen Lake just west of the park triggered a landslide that killed 28 people.
(© 2009 CBS Broadcasting Inc. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. The Associated Press contributed to this report.)
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