-- Robert B. Smith, professor of geophysics - office (801) 581-7129,
-- Lee Siegel, science news specialist, University of Utah Public
Relations - office (801) 581-8993, cellular (801) 244-5399,

Some Erupted More Often, Others Less Often After Big Jolt 2,000 Miles

    May 27, 2004 - A powerful earthquake that rocked Alaska in 2002
not only triggered small earthquakes almost 2,000 miles away at
Wyoming's Yellowstone National Park - as was reported at the time - but
also changed the timing and behavior of some of Yellowstone's geysers
and hot springs, a new study says.

    "We did not expect to see these prolonged changes in the
hydrothermal system," says University of Utah seismologist Robert B.
Smith, a co-author of the study in the June issue of the journal

    While other large quakes have been known to alter the activity
of nearby geysers and hot springs, the Denali fault earthquake of Nov.
3, 2002, is the first known to have changed the behavior of such
hydrothermal features at great distances, according to Smith and his
colleagues. They say the magnitude-7.9 quake was one of the strongest of
its type in North America in the past 150 years.

    Smith conducted the study with Stephan Husen, a University of
Utah adjunct assistant professor of geophysics who works at the Swiss
Federal Institute of Technology; Ralph Taylor, an engineer who designs
geyser monitoring equipment at Yellowstone National Park; and Henry
Heasler, Yellowstone National Park's geologist.

    Less than 18 hours after the Denali earthquake in Alaska, Smith
and colleagues at the University of Utah Seismograph Stations reported
the major jolt had triggered more than 200 small earthquakes in
Yellowstone - something widely reported by news media in the days
following the quake.

    Smith now says the triggered quakes at Yellowstone numbered more
than 1,000 within a week of the Denali quake - if the count includes
tiny temblors that were not "located," meaning their epicenters and
depths were not determined. He says the quakes ranged in magnitude from
minus 0.5 to just under 3.0. (Tiny quakes have negative magnitudes
because modern seismic equipment can detect quakes smaller than was
possible when the logarithmic magnitude scales were devised.)

    Most of the triggered quakes were centered near geysers and hot

Strong Earthquakes as Seismic and Geothermal Triggers

    Scientists once believed that an earthquake at one location
could not trigger earthquakes at distant sites. That belief was
shattered in 1992 when the magnitude-7.3 Landers earthquake in
California's Mojave Desert triggered a swarm of quakes more than 800
miles away at Yellowstone, as well as other temblors near Mammoth Lakes,
Calif., and Yucca Mountain, Nev.

    The magnitude-7.5 Hebgen Lake, Mont., quake northwest of
Yellowstone - a 1959  disaster that killed 28 people - triggered changes
in Yellowstone's geysers and hot springs, something not unexpected for a
strong quake nearby.

    Smith believes the Denali fault ruptured in such a direction -
from northwest to southeast - that the brunt of its energy and its
powerful surface waves were aimed southeast toward Yellowstone. As a
result, the stresses rippling through the ground at Yellowstone were 200
to 300 times greater than if the Denali quake's waves were aimed
elsewhere, he says.

    As the Denali quake's surface waves arrived at Yellowstone,
changes in hydrothermal activity first were noted at the 100 Spring
Plain hot spring system in Norris Geyser Basin.

    "Several small hot springs, not known to have geysered before,
suddenly surged into a heavy boil with eruptions as high as 1 meter
[about 39 inches]," Smith and colleagues wrote in Geology. "The
temperature at one of these springs increased rapidly from about 42 to
93 degrees Celsius [about 108 to 199 degrees Fahrenheit]" and became
much less acidic than normal. "In the same area, another hot spring that
was usually clear showed muddy, turbid water."

    Meanwhile, some geysers erupted more frequently than normal,
while others erupted less frequently.

    Yellowstone has more than 10,000 geysers, hot springs and
fumaroles (steam vents), and scientists monitored how often 22 of the
geysers erupted during the winter of 2002-2003. Eight of the 22
"displayed notable changes in their eruption intervals" after the Denali
quake, 10 showed no significant changes and the other four were too
erratic in the timing of their eruptions to determine if the quake
changed them, the researchers wrote. Of the eight that changed:

    -- Geysers that erupted more frequently following the Denali
quake included Daisy, Depression, Plume and Riverside geysers in Upper
Geyser Basin, and Pink Geyser in Lower Geyser Basin.

    -- Geysers that erupted less frequently after the Denali quake
included Castle and Plate geysers in Upper Geyser Basin and Lone Pine
Geyser in West Thumb Geyser Basin.

    Most geysers returned to their normal timing days to months
after the Denali quake.

    Oddly, geysers affected by earlier nearby earthquakes - most
notably Old Faithful and Grand Geyser in Upper Geyser Basin - were not
affected by the Denali earthquake.

How the Denali Quake Sparked Yellowstone Activity

    Scientists do not know if the strong surface waves from the
Denali quake independently triggered Yellowstone's small quakes and
changes in geyser activity. Smith suspects not. He believes the Denali
quake's waves affected the geysers by changing water pressure in
underground conduits or "pipes" that feed the geysers. Such changes -
which in some cases would have made hot water "flash" explosively into
steam - would have altered the pressure on adjacent faults, triggering
small earthquakes nearby. That would explain why the quakes were
clustered around geyser basins.

    Why did some geysers erupt more often and others less often? The
researchers believe that when the Denali quake waves rippled through
Yellowstone, they jarred loose minerals that had sealed some underground
hot water conduits.
In some cases, that allowed superheated, pressurized water to flow more
freely to make geysers erupt more often. In other cases, the rupturing
of subterranean mineral seals enlarged the size of the conduits
supplying geysers, reducing water pressure so those geysers erupted less
often. Smith speculates that yet other geysers remained unchanged
because they did not have pent-up gas and water pressure and were not
affected by the Denali quake's surface waves.

    The Denali quake also generated noticeable water waves in
Seattle's Lake Union, Louisiana's Lake Pontchartrain and in swimming
pools on the East Coast. It also triggered small quakes in California's
Geysers geothermal area, which is north of San Francisco, and in eastern
California's Long Valley, which, like Yellowstone, is a caldera, or
giant volcanic crater created by cataclysmic prehistoric volcanic

    The Denali quake also triggered a few small quakes in Utah, and
Smith says it is possible some of those quakes occurred near
little-known hot springs along the Wasatch fault at the base of the
Wasatch Range.

    Smith says the fact that the Denali quake triggered geyser and
hot springs changes at Yellowstone raises an interesting question:
"Could large earthquakes closer to Yellowstone trigger hydrothermal

    Such steam-and-hot water explosions in prehistoric times blasted
out a hole that now is Mary's Bay on Yellowstone Lake. One such
explosion has occurred roughly every 1,000 years since the glaciers
receded from Yellowstone roughly 14,000 years ago.

    Smith says there is no evidence prehistoric quakes triggered
those blasts. And such explosions were not triggered by the
magnitude-7.5 Hebgen Lake, Mont., quake in 1959 or the magnitude-7.3
Borah Peak, Idaho, quake in 1983.

    Nevertheless, a big quake near Yellowstone with its surface
waves aimed the right way conceivably might "cause large hydrothermal
eruptions," says Smith. "I would hypothesize that is certainly

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