How can ASU scientists Randy Cerveny and John Shaffer tell how much rain fell at Devil's Hole a half-million years ago? The clues are in the calcite.
Calcite is a chemical that's found in the dirt that lines the sides of Devil's Hole. When it rains, calcite mixes with water. By carefully measuring each year's layer of calcite, Cerveny and Shaffer can tell how much rain there was that year.
Devil's Hole is exactly that—a big hole that's approximately 500 feet deep. It's so deep that nearly 500,000 years' worth of calcite deposits rest inside.
Analyzing the depth of each calcite layer is much like analyzing a tree's growth by studying its ring pattern. Scientists use both methods to determine how much rain fell each year. When a tree's rings are wider, it means there was more rainfall that year. That's because the tree had more water to help it grow. Calcite layers provide similar records. Those layers are deeper for years when more rain fell.
Cerveny and Shaffer used calcite, rather than tree ring data, because the calcite patterns at Devil's Hole date back more than 500,000 years. Tree rings usually only provide data for a few hundred years.
Once they took all of the calcite measurements, the ASU weather detectives were ready to put their computers to work. Their biggest problem was turning a bunch of ordinary numbers into a rainfall prediction for Yucca Mountain. Shaffer created detailed mathematical equations, called algorithms, to help him pinpoint rainfall patterns.
The model he built on the computer showed that the Earth would get colder. But, how would cooling change the amount of rainfall in Nevada? Looking for clues, Shaffer and Cerveny pored over records of weather patterns for the world and for Northeast Canada.
Northeast Canada is where the last great ice sheet formed during the last Ice Age. It is an important spot to study. Scientists already know that Canada became dryer during the last Ice Age.
But the Devil's Hole data suggested that Nevada had gotten wetter. It was up to the ASU weather detectives to explain that difference.
Their answer came directly from the weather patterns at both sites. Shaffer realized that they were opposites. When it was hot at one site, it was cold at the other, and vice versa. Shaffer used that knowledge to change his computer model.
Bingo! The new findings closely matched the actual calcite patterns he and Cerveny found at Devil's Hole. That meant it was now possible to scientifically explain many of the troubling differences between Devil's Hole and other studies that had used the Canadian data.
It also meant that Cerveny and Shaffer could reliably predict rainfall patterns at the Yucca Mountain nuclear waste storage site during the government's 10,000-year time frame.
—Lindsey Michaels