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TONOPAH, Nev. — At one time, they spewed ash and lava. Now, they slumber in the southern Nevada desert where President Bush wants to build the nation’s nuclear waste dump. 

Eight cinder cones have erupted within 30 miles of the proposed Yucca Mountain site over the past 1 million years, and the desert is dotted with more than a dozen older volcanoes. 

The last eruption was about 77,300 years ago at the Lathrop Wells cinder cone nine miles south of Yucca Mountain, itself a much older volcanic ridge. 

Although federal scientists downplay the volcanic threat to the site 90 miles northwest of Las Vegas, a new state-funded study questions the wisdom of entombing 77,000 tons of radioactive waste in what geologists consider a dormant volcanic field. 

“There’s a good likelihood there will be another eruption. It could be tomorrow or it could be sometime in the future,” said Eugene Smith, a University of Nevada-Las Vegas geology professor who headed the study under contract with the Nevada Nuclear Projects Agency. 

The repository is strongly opposed by top Nevada elected officials, who have accused the federal government of ignoring safety concerns. The agency is a branch of the Nevada governor’s office. 

Energy Department scientists insist there’s only a 1-in-70 million chance of volcanic activity at Yucca Mountain during the 10,000 years that the radioactive waste must be contained. 

But in an article in the current edition of the Geological Society of America’s journal GSA Today, Smith suggests the Energy Department might be underestimating the volcanic risk. 

Citing rock chemistry as well as recent geochemical and geophysical studies by other scientists, Smith contends the Yucca Mountain area is linked by a belt of abnormally hot mantle to the more active Lunar Crater volcanic field 60 miles to the northeast. 

At least 14 volcanic eruptions have occurred in the Lunar Crater area in the past 1 million years, with the last two forming lava fields about 38,100 years ago. 

Lunar Crater and Yucca Mountain have been Nevada’s most active volcanic fields over the past 6 million years, according to Smith’s studies. 

If the two fields share a common area of hot mantle, Smith argues, volcanic recurrence rates of 11 to 15 events per million years in the Lunar Crater field are possible at Yucca Mountain. The Energy Department now sets volcanism probability at 3.7 to 12 events per million years at Yucca. 

Smith acknowledges his findings about hot mantle will generate considerable controversy among volcanologists. 

“This is the first time someone has proposed linking the two volcanic fields and it will be debated for a while by scientists,” Smith said. If accepted, however, scientists would view a volcanic eruption at Yucca Mountain as more likely. 

Energy Department scientists dispute Smith’s findings, saying they interpret the information differently and view Yucca Mountain and Lunar Crater as two distinct fields. 

Even if Lunar Crater’s higher rate of volcanism is factored into probability models, the chance of volcanic activity at Yucca Mountain still would be unlikely, they said. 

“We believe the two volcanic fields come from different source zones and operate independently of each other,” said DOE geologist Eric Smistad, who heads a federal team studying volcanism at Yucca Mountain. 

“We think we’ve got to the point in our volcanism studies that we’re on solid ground. ... We’re confident that volcanism won’t jeopardize the long-term safety of the repository.” 

But Bruce Crowe, the Energy Department’s top volcanic investigator at Yucca Mountain from 1980 to 1995, said Smith is a credible researcher whose findings should not be ignored. Crowe’s own studies concluded Lunar Crater and Yucca Mountain are separate fields. 

“Obviously, some scientists will say Gene is bringing some bias into the study,” Crowe said. “But I respect Gene for maintaining neutrality and fairness, even though he was under contract with the state of Nevada. I think he falls under the realm of sound science.” 

Smith’s findings will stir controversy partly because volcanic data are notoriously difficult to interpret, Crowe said. But that difficulty also allows conclusions to vary widely while still being considered credible interpretations. 

“I consider Gene’s speculations to be credible,” Crowe said. “They should be looked at carefully.” 

Duane Champion, a U.S. Geological Survey volcanologist in Menlo Park, Calif., said a link between the Yucca Mountain and Lunar Crater fields is possible. 

Another researcher found that volcanic eruptions in the Great Basin have occurred at the same time in places separated by up to 100 miles, he said. The Great Basin is a vast expanse that covers nearly all of Nevada. 

Smith’s findings “lead me ... to be curious about the chemistry arguments he’s bringing to bear,” Champion said. “It’s just a theory now. But I’m quite intrigued he could have merit to the argument.” 

Smith’s study also found that volcanism in the Yucca Mountain-Lunar Crater zone has been episodic, with three peaks of volcanism over the past 9.5 million years and quiet periods in between lasting 1 million to 2 million years. 

Smith said it’s been nearly 1 million years since the last peak of activity, but it’s unclear whether the zone now is at the beginning, middle or end of the current period of low activity. There have been three eruptions in the past 77,300 years. 

“Speculatively, these observations may indicate the end of the current period of low activity and an increase in the rate of eruption in the near future,” he wrote. 

But Smistad said the Department of Energy already has factored the area’s history into its probability models and doesn’t view it as a threat. The department has conducted volcanism studies at Yucca Mountain for more than two decades. 

“Gene is trying to suggest that volcanism is waxing and becoming more active in the Great Basin,” Smistad said. “But our 10 experts took all that into consideration and concluded that volcanism in the Great Basin is waning and dissipating.” 

Both the Nuclear Regulatory Commission and a federal technical oversight panel will take a position on Smith’s findings after hearing from both sides. 

“It’s surely something we would expect DOE to address,” said Bill Reamer, deputy director of the NRC’s waste management division. “Volcanism and the probability of volcanism is a key issue.”