Sept. 12, 2006 — It may be quiet now, but about 80,000 years ago the land just 10 miles from the proposed U.S. High-Level Nuclear Waste Depository at Yucca Mountain, was rocking and rolling with earthquakes and volcanic eruptions, says a government geologist.
By digging trenches through three Yucca Mountain faults in Nevada and studying the rocks within, paleoseismologists found evidence that earthquakes and eruptions tend to conspire in the Yucca Mountain area, making for a geologically rowdy scene.
Tom Parsons, a geologist with the U.S. Geological Survey and his colleagues gathered this data and studied the upheavals of the past with a computer model.
“What we kind of stumbled over is some volcanic ash at the bottom of earthquake fissures,” says Parsons, describing the initial key discovery by paleoseismologists.
The fissures are shallow cracks in the ground that can form during strong quakes, and then fill up with sediments in pretty short order. “Days or weeks, we can’t tell for sure,” he said of the refilling.
That these fissures had ash in them is startling because it means either the nearby 80,000-year-old Lathrop Wells volcanic cinder cone was spewing ash into the air at the same time as the earthquake, or that the eruption had occurred just days or weeks before the quake. Before this discovery, geologists had tended to think of the quakes and eruptions in the Yucca Mountain area as separate and largely unrelated events.
With this new tantalizing clue to the clustering of at least the Lathrop Wells eruption and earthquakes, Parsons and his colleagues set about making a model to simulate how the gradually spreading crust of the Earth in the Yucca Mountain region might create the troublesome coincidence.
“The whole area is being stretched,” said Parsons.
Faults that cut through the region allow blocks of crust to slide alongside each other in all sorts of directions and help the crust to stretch — the same way books on a shelf can cover more of the shelf when they are tilted and sliding along each others’ covers.
