While the massive volcano that formed Yucca Mountain is long extinct, the state is concerned that younger volcanoes dotting the desert to the southwest could someday push molten lava through Yucca Mountain. The volcanoes are not as stable as earlier believed, state officials say. However, the DOE has concluded the seven nearby volcanoes are not likely to erupt in the next 10,000 years - and that it's even more unlikely lava would reach the repository. The state has more disturbing worries about earthquakes. The area is crossed with a series of parallel faults a few miles apart, an unusual configuration.
Geologists guess they eventually connect.
To avoid the faults, the waste repository would be built between two of them - the Solitario Fault and the Ghost Dance Fault. As recently as 1992, an earthquake below Little Skull Mountain 12 miles from Yucca Mountain registered 5.6 on the Richter Scale and shook the DOE project office. Even with this, Sullivan maintains there is little risk to the repository. Yucca Mountain project officials point out earthquakes are known to shake the surface of the earth more than the rock within it. Miners in China have emerged after a day's work deep below, unaware that severe quakes had rocked the area.