Judith Lewis' story "Mountain of Doubt" in the Jan. 19, 2009, issue of HCN provides an admirably accurate and balanced description of the history of Department of Energy-led efforts to establish Yucca Mountain as a safe repository for the nation's high-level nuclear waste.

Beyond the politics, Lewis explains, "Doubts about Yucca Mountain's geologic suitability have piled up as well. A panel of scientists put the chances of igneous disruption in the ridgeline's ancient field of volcanoes at one in 6,250 over the next 10,000 years." She points out that even if one in 6,250 seems low, "in most of the United States the probability of a volcano erupting is zero."

I was a member of the panel mentioned by Lewis. A summary of our results was published in Science (Nov. 8, 1996, v. 274, p. 913-914). Our marching orders (10 of us selected as experts in volcanology) were to determine the probability that an igneous dike (a sheet of molten magma) would intersect the repository footprint in the coming 10,000 years. I voiced concern about what the consequences to the repository would be if a dike were to feed a violent volcanic eruption. A style of eruption called phreatomagmatic (during which 2,000 degree Fahrenheit magma encounters groundwater and thus triggers violent steam explosions) could be particularly damaging to the repository.

The Energy Department has recently sponsored studies to model the effects to the repository in the event of a volcanic eruption, excluding the phreatomagmatic style. To which I caution: Ignoring a potential problem does not make it disappear.

Of all possible repository locations within the Nevada Test Site, none is closer to the region's youngest volcanoes than Yucca Mountain. A half-dozen volcanoes are located in Crater Flat, just west of Yucca Mountain. These are less than 1,000,000 years old. The youngest is 80,000 years old, and its deposits include evidence of a possible phreatomagmatic phase of eruption.

To see what a phreatomagmatic eruption can do, drive 60 miles west of Yucca Mountain to Ubehebe Crater Volcano at the north end of Death Valley National Park. There, about 2,000 years ago, a phreatomagmatic eruption blasted a crater a half-mile wide and 1,000 feet deep.

I am on public record as favoring new electrical generating capacity at nuclear power plants. However, I submit that using Yucca Mountain for storage would bring exposure to an uncomfortable, and some would argue unacceptable, level of volcanic hazard.

Wendell A. Duffield
Adjunct Professor,
Geology Department,
Northern Arizona University
Flagstaff, Arizona