CHRIS MERRILL Star-Tribune environment reporter | Posted: Wednesday, June 4, 2008 12:00 am
LANDER - Old Faithful, as it turns out, has been getting a bit sluggish during the dry times.
Geologists have known for years that earthquakes can affect geyser activity, but a new study suggests that climate, and even seasonal changes in precipitation, can also have an impact on these hot spring eruptions.
Shaul Hurwitz, a researcher with the U.S. Geological Survey, along with Stanford University statistician Ashish Kumar and two National Park Service scientists, have discovered that changes in the supply of water to a geyser's underground plumbing can influence the amount of time between eruptions.
Hurwitz's study, published in this month's issue of the academic science journal Geology, appears to confirm what might seem, in retrospect, an obvious supposition: When geysers such as Old Faithful are fed more water, they erupt more frequently. And when there is less water flowing underground, the wait between eruptions gets longer.
Even though people have been studying geysers, particularly Old Faithful, for more than a century, there is still quite a lot that isn't understood about these eruptions - especially when it comes to the effects of external forces on the rate and intensity of the explosions, Hurwitz said by phone this week from Menlo Park, Utah.
"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 geysers in Yellowstone National Park, including Old Faithful, now have sensors in their outflow channels that constantly record the temperature, and keep a continuous log of eruptions. These sensors, operated by the National Park Service and the Geyser Observation and Study Association, represent a huge leap forward in the amount and quality of information scientists have about these hydrothermal eruptions, Hurwitz said.
Before the sensors were available, all of the known and recorded information about the rate and intensity of the geyser explosions came from periodic, in-person observations, mostly by park personnel.
Hurwitz's study examined data collected from sensors in five reliable geysers, including Old Faithful, from 1997 to 2006.
The winter of 1997 in Yellowstone and the surrounding mountains was the wettest winter in at least the last 100 years, Hurwitz said, but precipitation rates decreased steadily after that, through 2006.
"Coupled with this decrease in precipitation, we see an increase in eruption intervals with all the geysers we analyzed," he said.
While experts are still debating how much influence such things as climate, barometric pressure and precipitation have on geysers, recently scientists have been able to show how three earthquakes since 1959 have each changed the geology enough to lengthen the period of time between Old Faithful's eruptions.
Hurwitz's study suggests that dry periods have themselves added a minute or two to the wait between Old Faithful's hot showers.
While the world's most famous geyser has been reliable for at least 135 years, for most of the second half of the 20th century it erupted every 50 to 70 minutes. Since 1983, following an Idaho earthquake, that interval lengthened, steadily, to 80, 85 and, most recently, every 91 minutes, on average.
A dryer climate regionally should only slow the eruptions further, Hurwitz said.
"Our grandchildren will have to wait longer for Old Faithful to erupt," he said.
Al Nash, chief of public affairs with Yellowstone National Park, said research like this, which adds to the knowledge base about the park, is "exciting." It should eventually find its way into the park's educational materials and will be included in presentations to visitors.
"As much as it may surprise some people, we're still at a point where there is much more for us to learn about the dynamics of the systems that visitors see when they travel to Yellowstone, and how (these systems) interact with each other," Nash said. "It's sort of like peeling an onion. The more we learn, the more avenues researchers find to explore further."
About Yellowstone's geysers
* Fewer than 1,000 geysers are known to exist worldwide, with more than half of them in Yellowstone National Park.
* Old Faithful Geyser was named in 1870 during the Washburn-Langford-Doane Yellowstone expedition, and was the first geyser in the park to be named.
* In 1959, Old Faithful was erupting, on average, every 61 minutes, until an earthquake on Aug. 17 changed the eruption intervals, increasing the wait between showers to more than 65 minutes by 1960.
* The 1975 Yellowstone Plateau Quake again changed the geology enough to lengthen the intervals between Old Faithful eruptions from about 66 minutes to almost 73 minutes by 1980.
* A third quake, this one near Idaho's Borah Peak in 1983, almost immediately caused the wait between Old Faithful eruptions to increase to over 76 minutes.
* The current interval between eruptions is about 91 minutes, with about a minute or two due to the long-term drought.
* Video of Old Faithful eruptions can be viewed online at www.nps.gov/archive/yell/oldfaithfulcam.htm
Source: U.S. Geological Survey and Shaul Hurwitz, USGS researcher
Environment reporter Chris Merrill can be reached at chris.merrill@trib.com or at (307) 267-6722.