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MEMORANDUM TO ALL VIETNAM VETERANS
THE YEAR 2007
 
 
Yellowstone is jostled by 250 small earthquakes in three days
By MEAD GRUVER, Associated Press Writer Mead Gruver, Associated Press WriterMon Dec 29, 2008
 

CHEYENNE, Wyo. – 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.

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.

 
 

Is  Yellowstone  About  to  Blow?

http://www.unknowncountry.com/news/?id=6558



Click to enlarge
Almost a year ago, we asked the question, when will Yellowstone blow? The Yellowstone "supervolcano" has risen at a record rate since mid-2004. A blob of molten rock that size of Los Angeles that has been discovered 6 miles beneath the slumbering volcano could be the problem.

Seismologist Robert B. Smith reassures us that "there is no evidence of an imminent volcanic eruption or hydrothermal explosion. That's the bottom line. 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, 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."

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. The upward movement of the Yellowstone caldera floor—almost 3 inches per year for the past three years—is more than three times greater than ever observed since such measurements began in 1923.

Smith’s associate, Wu-Lung Chang, says, "To say if there will be a magma [molten rock] eruption or hydrothermal [hot water] eruption, we need more independent data." So will Yellowstone blow? The truth is, we don't know.

ANOTHER thing we don't know is how long this website and our excellent radio shows can keep going without more help from YOU. If you value the truth— about all sorts of subjects—than you value US, so make sure we’ll be here tomorrow: subscribe today. And if you want to help us EVEN MORE, please click on the new "donate" tab on our homepage.

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28-Nov-2007

Related Stories:
15-Mar-2007:
When Will Yellowstone Blow?
23-May-2006: Yellowstone Still Threatens to Blow
10-Mar-2005: Is a Supervolcano on the Way?
05-Dec-2004: BBC Drama Says Yellowstone Could Kill a Billion
20-Sep-2004: Earthquakes Swarming on Cal-Nev Border
02-Jun-2004: Earthquake Changed Yellowstone
25-Mar-2004: Ominous Signs at Yellowstone
19-Jan-2004: Yellowstone Supervolcano will Devastate Wide Area
14-Jan-2004: Is Yellowstone Worse Than They Say?
01-Dec-2003: Scientist Says Yellowstone Bulge Could Mean Explosion
 
November 26, 1995

Earthquake After Earthquake Shaking Yellowstone Park

It has been a shaky few months here. More than 1,200 earthquakes have rumbled Yellowstone National Park this year, up from 800 last year and 179 the year before.

While this park is world famous for its skyrocketing geysers, simmering hot pools and bubbling mudpots, what is less well known, because it is invisible, is the underground volcano that created these geothermal attractions. Slumbering fitfully beneath sagebrush-studded meadows and lodgepole-pine forests, this volcano, known as a caldera, is believed to be causing the strings of earthquakes, known as swarms. It is by far the largest "hot spot" in North America and one of the largest in the world.

The surrounding region is one of the most seismically active in the country, and some of the quakes there have been quite large.

On Aug. 17, 1959, for example, a quake of magnitude 7.5 shook an area west of Yellowstone, jarring loose some 80 million tons of rock -- half a mountain -- and burying 25 sleeping campers at a national forest campground. It also dammed the Madison River and created Quake Lake.

In 1983, the 7.3 magnitude Borah Peak quake, centered about 100 miles west of the park, shook Idaho, killing two children, and lengthening the period between eruptions of Old Faithful, from an average of about 69 minutes to 77 minutes.

With the help of locational satellites and tomographic imaging, which uses sound waves to create a subterranean profile, scientists have determined that there is partly molten rock five to six miles below the surface, beneath a crust that has been repeatedly fractured by eruptions for two million years. The movement of that molten rock, called magma, or of hot water or gasses beneath the geologically unstable region, is probably causing the quake swarms, said Robert B. Smith, a seismologist at the University of Utah in Salt Lake City who, with Lawrence W. Braile, published a paper about the caldera last year in The Journal of Volcanology.

With five major geological fault lines buried in it, the caldera has a much more widespread effect in the Northern Rockies than was previously thought, they say. The movement of the molten and semi-molten rock could cause earthquakes as far south as the Wasatch fault in Utah, as far north as Bozeman, Mont., central Idaho to the west and Cody, Wyo., to the east, Dr. Smith said.

Earthquakes are most often thought of as a sharp jolt followed by a series of aftershocks, the largest of which is usually an order of magnitude smaller. The aftershocks then trail off over time. The swarms that occur in volcanic regions "start with one quake, build to a crescendo and then die off," Dr. Smith said.

"A swarm can last hours, days or a month," he said.

Dr. Smith said not enough was known about the subterranean structure of the caldera to say if the recent quake swarms suggest that more quakes, or larger quakes are to be expected. There is no reason to believe that a major earthquake is going to shake Yellowstone anytime soon, he said, or that the caldera is ready to explode, although both are always possible. The park has 24 seismic stations that are constantly monitored.

Late in June and in early July, a series of 550 small earthquakes, some with a magnitude as high as 3.1, rattled the Mount Haynes area a few miles east of the town of West Yellowstone. Then, starting on Oct. 6, more than 100 earthquakes up to magnitude 4.3 shook an area near Mount Sheridan and Lewis Lake, in the park's southern end.

"I doubt we could have volcanism here without plenty of advance warning," said John Varley, research coordinator for the park. "The earthquake guys can't say that."

The existence of the caldera was not known until the 1950's. And it was not until the mid-1980's, when a park geologist was comparing aerial photographs taken a decade apart of Yellowstone Lake, in the center of the park, that clues to the enormous movement of the caldera began to emerge.

The photos showed the water level at the south end of Yellowstone Lake was rising. Scientists discovered that the caldera, which sits under the northern portion of the lake, was pushing up the lake's northern tip, causing water to run to the southern end.

Measurements by Dr. Smith and others show that from 1923 until 1977, the ground above the caldera was pushed up two feet. From 1977 until 1985, the ground gained an additional foot, rising at what geologists consider a remarkable rate of more than an inch a year.

Then, during a one-month period in 1985, a large swarm of some 2,000 quakes as strong as magnitude 4.5 shook the park's northwest side. A short time later, the caldera stopped rising and started to drop, and it continues to do so at the rate of about half an inch a year.

Dr. Smith theorized that the dropping of the landscape might be one of the reasons for the earthquakes. As the caldera, and thus the park, sinks, it occupies volume, and might be causing magma and hot water to squirt out laterally into the highly fractured crust. "As this stuff intrudes through the broken-up piece of crust," Dr. Smith said, "it increases the pressure and causes a lot of little earthquakes."

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