Friday, May 13, 2005
Not enough warnings about possible volcano eruptions
Monitoring is inadequate at those and 11 other volcanoes rated as "very high threats," scientists say in a new report from the U.S. Geological Survey. Gaps in monitoring exist at another 37 volcanoes - most of them in Alaska - classified as "high threats."
Threat levels are based on such factors as proximity to population centers and commercial airline routes, history of activity and explosive potential.
Mount Hood has the fourth-highest threat score in the nation. South Sister, 70 miles east of downtown Eugene, is ranked sixth. Although many think of it as long dormant, Crater Lake is 10th on the threat list of 169 U.S. volcanoes.
Some of the danger posed by Cascades volcanoes comes from the snow and ice that would melt in an eruption, causing massive debris flows called lahars. As the 1980 eruption of Mount St. Helens demonstrated, these deadly flows can wipe out bridges, roads, houses and miles of forests.
More seismometers and other equipment will help the USGS develop an early warning system for volcanoes, the agency says.
The emphasis on better monitoring comes partly in response to new awareness of how quickly volcanoes can rumble back to life, said John Ewert, a geologist at the Cascades Volcano Observatory in Vancouver, Wash., and one of the report's authors.
Mount St. Helens began erupting again last fall just a week after scientists detected a series of earthquakes beneath the mountain, and that's one of the most closely monitored volcanoes in the world.
"You don't want to be in a position of playing catch-up with a volcano," Ewert said. "Once it starts a period of activity, you never know how long you have."
And it can be difficult in winter to quickly deploy equipment at volcanoes in the Cascades range, he said.
The warning signs preceding an eruption also can be hard to catch. Alaska's Mount Redoubt blew in 1989, disabling all four engines of a Boeing 747 approaching Anchorage. Geologists had detected nothing larger than a magnitude 1 quake in the year preceding the eruption.
"Some of them can behave in quite subtle ways before they erupt," Ewert said.
South Sister's high threat level is due in part to a slight uprise in the landscape west of the 10,358-foot peak. The bulge has grown an estimated 8 to 10 inches in the past seven years in response to magma accumulating three to four miles underground, according to the USGS.
The deformation, as scientists call it, has developed largely without associated earthquakes. That and the '89 Redoubt eruption have shown one can't rely on a swarm of quakes to justify beefing up monitoring at volcanoes, Ewert said.
"The model we'd been operating under has been shown to have some flaws in it," he said. "What South Sister has shown us is volcanoes can enter into a state of unrest with no seismic activity."
More seismometers and other instruments placed in the right locations will help geologists detect slight ground movements they may be missing now, he said. Plus, if an eruption suddenly looks imminent, less gear will need to be rushed into the field.
The USGS has put in more seismometers near South Sister and plans to add more satellite-based systems to detect ground swelling in the area this summer. But even more is needed, Ewert said.
"It's still a fairly skeletal monitoring system," he said. "To characterize the unrest, we need a network of stations. The stations there now don't allow us to really get at the process which is making the changes happen."
Putting out a new seismometer can cost $10,000 to $15,000, and a GPS station can cost $20,000 to $25,000, said W.E. "Willie" Scott, also a geologist at the volcano observatory in Vancouver.
"We certainly wouldn't want the system to go to an eruption with what we have there now," Scott said.
The 10 most threatening volcanoes in the United States according to a new U.S. Geological Survey report:
1: Mount Kilauea, Hawaii (erupting)
2: Mount St. Helens, Wash. (erupting)
3: Mount Rainier, Wash.
4: Mount Hood
5: Mount Shasta, Calif.
6: South Sister
7: Lassen Volcanic Center, Calif.
8: Mount Mauna Loa, Hawaii (unrest)
9: Mount Redoubt, Alaska
10: Crater Lake