BILLINGS, Mont. - A major earthquake that hit Alaska in 2002 set off a flurry of smaller quakes in far-off Yellowstone National Park and changed eruption intervals in several geysers, according to a new study.
Scientists say the Denali fault earthquake, which registered a magnitude 7.9 and hit in November 2002, is believed to be the first in modern times in North America to trigger large-scale changes so far away.
"What's really kind of interesting ... is the recognition that large earthquakes at very large distances can have really profound effects on Yellowstone geysers, given the orientation of the waves and the amplitude of the particular earthquake," said Robert Smith, a geophysics professor at the University of Utah who worked on the study.
The lead author was Stephan Husen, an adjunct assistant geophysics professor at the university.
According to the study, which appears in the June issue of the journal Geology, changes in eruption intervals in several Yellowstone geysers began in the hours after the Denali earthquake.
"Intense swarms" of local earthquakes also occurred near hydrothermal systems that saw such changes, the study said. Within a week of the Denali quake, Smith said more than 1,000 earthquakes, many of them tiny and near hot springs or geysers, occurred at Yellowstone.
Researchers believe surface waves from the large earthquake affected geysers by altering water and steam pressure in underground systems feeding the features, he said.
Changes like that would have affected pressure on faults in proximity to the hydrothermal systems and set off small quakes - a possible explanation for the number of quakes that occurred near geyser basins, he said.
Earthquakes, Smith believes, keep geysers alive by periodically shaking loose minerals that can clog pathways for water.
In the study, researchers monitored eruption intervals of 22 geysers during the winter of 2002-03. Of those geysers, they found that eight showed notable changes. Four were deemed too erratic to show any effects, and 10 showed no significant changes, the study said.
Daisy Geyser was among those affected, showing a rapid decrease in the eruption interval after the earthquake and returning to near pre-quake intervals over weeks, the study said.
Researchers added that the geysers Castle, Plate and Plume were among those with short-term irregularities that lasted for a few days.
Lone Pine Geyser showed a gradual rise in eruption intervals that the study says peaked three weeks after the big earthquake.
Smith said most features returned to normal in the days and months after the large quake, something he expected.
"The earth wants to go back to equilibrium," he said.
The quake was centered in a remote and sparsely populated area southeast of Denali National Park, 90 miles south of Fairbanks, but was felt throughout much of Alaska.