'Young' volcano near nuclear waste site.

'Young' volcano near nuclear waste site

New research indicates the Department of Energy significantly overestimated the age of a volcano near Yucca Mountain, Nev., the proposed site for the nation's first high-level nuclear waste dump. The age revision fuels an already heated controversy over the site's suitability as a safe storage place for nuclear power plant wastes, which remain dangerous for 10,000 years.

The volcano, called the Lathrop Wells cone, lies about 20 kilometers from the proposed location for the underground waste repository. Energy Department studies in the mid-1980s indicated the volcano last erupted around 270,000 years ago. But a comparison of Lathrop Wells with another volcano now suggests a much younger age of less than 30,000 years, and probably even less than 20,000, report Stephen G. Wells of the University of New Mexico in Albuquerque and his colleagues.

"What surprised us was the relatively youthful appearance of the volcano," says Wells.

By studying the extent of erosion and soil development on Lathrop Wells, the researchers compared this volcanic cinder cone with a similar cone in southeastern California, indirectly dated at about 15,000 to 20,000 years old. The comparison suggests the volcanoes are of equal age, they assert in the June GEOLOGY. Wells says some experimental dating techniques indicate that Lathrop Wells formed as recently as 20,000 years ago.

Other scientists dispute the notion that Lathrop Wells erupted that recently. Brent Turrin of the U.S. Geological Survey in Menlo Park, Calif., has used the radioactive decay of potassium-40 into argon-40 to date lava flows from Lathrop Wells and the California cone. His findings suggest both volcanoes last erupted lava more than 90,000 years ago. While Turrin acknowledges that the volcanoes look young, he says his work raises a question: "What is young when you look at a cinder cone?"

Wells says the age discrepancy may signal a problem with the standard theory that cinder cone eruptions happen all in one shot during a short period of time. Instead, the volcanoes might erupt lava and then, tens of thousands of years later, create a cinder cone.

Carl A. Johnson, a geologist with the State of Nevada's Agency for Nuclear Projects in Carson City, contends that the new information about Lathrop Wells could constitute a cause for concern. "It is certainly suggesting to us that there's some major questions as to whether the site is a suitable one or not."

Johnson says a volcanic eruption near the repository could trigger changes in the groundwater system, perhaps raising the water table underneath the buried repository. That could enable radioactive elements to escape into the environment faster than the regulations allow.

But Bruce M. Crowe, a coauthor of the GEOLOGY report, maintains that the young age of Lathrop Wells -- and the chance of a future eruption -- would not significantly threaten the repository. Crowe, a volcanologist with Los Alamos (N.M.) National Laboratories, heads the Energy Department team assessing volcanic hazards at Yucca Mountain. According to his calculations, the age revision for Lathrop Wells does not justify disqualifying the site.