BILLINGS, Mont. -- The major earthquake that hit Alaska in 2002 and set off a flurry of smaller quakes in far-off Yellowstone National Park also altered activity of hydrothermal features there, causing some geysers to go off more often, new research shows.

Scientists say the Denali fault earthquake, which registered 7.9 and hit in November 2002, is believed to be the first in modern times in North America triggering such 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 professor of geophysics at the University of Utah who was among those who worked on the study appearing in the June issue of the journal Geology.

The lead author was Stephan Husen, an adjunct assistant professor of geophysics at the university.

Changes in eruption intervals in several Yellowstone geysers began in the hours after the Denali earthquake, the study said.

"Intense swarms" of local earthquakes also occurred near hydrothermal systems that saw such changes, according to the study.

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.

A message left Friday for Yellowstone's geologist, who was also involved in the study, was not immediately returned.

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 geysers Castle, Plate and Plume were among those with short-term irregularities in behavior 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 said he expected. "The earth wants to go back to equilibrium," he said.