YELLOWSTONE NATIONAL PARK, Wyo. - New research suggests that several years of drought may have added a minute or two to the eruption cycle of Old Faithful geyser. The geyser used to erupt about every 61 minutes. That cycle lengthened to more than an hour and 15 minutes following earthquakes in 1959, 1975 and 1983.

Now, the eruption cycle for Old Faithful is just over an hour and a half.

Shaul Hurwitz with the U.S. Geological Survey spent nine years studying five geysers in Yellowstone including Old Faithful. The study period covered Yellowstone's wettest winter in a century as well as several years of drought.

Hurwitz speculates that the drought decreased Old Faithful's water supply and has lengthened the time between eruptions.

His study was published in this month's issue of the academic science journal Geology.

Hurwitz said people have been studying geysers for more than a century. But he said much remains to be learned about geyser eruptions, including what contributes to their intensity and frequency.

"Until recently we did not have good enough data to actually quantify the process," he said. "We now have instruments that actually measure when geysers erupt."

About 25 Yellowstone geysers including Old Faithful have sensors in them that constantly record their temperature and log eruptions.

Hurwitz's study examined data from five reliable geysers, including Old Faithful, from 1997 to 2006. The winter of 1997 in Yellowstone and surrounding mountains was the wettest in at least 100 years, but drought has prevailed in the area for much of this decade.

"Coupled with this decrease in precipitation, we see an increase in eruption intervals with all the geysers we analyzed," he said.

Hurwitz said a drier climate regionally should only slow the eruptions further.

"Our grandchildren will have to wait longer for Old Faithful to erupt," he said.