Yucca Mountain is located in southwestern Nevada, about 160 km northwest of Las Vegas, and has been the controversial site of a proposed high-level nuclear waste storage repository. Although the remote location of Yucca Mountain is an ideal site for storing nuclear waste, the active geologic setting causes concern among many in the scientific community and raises doubts on whether or not this location is safe. Understanding the geologic history and current seismic environment of this region is critical in making policy decisions regarding nuclear waste storage under Yucca Mountain.
Geologic History - Volcanism and Tectonics
Volcanic activity and tectonic stresses dominate the geologic history of the Yucca Mountain region. Yucca Mountain itself is made up of volcanic material called tuff. Tuff is consolidated and welded volcanic ash. Commonly associated with very large volcanic eruptions, tuff forms when massive amounts of volcanic ash are deposited and fuse together under the heat and pressure of overlying ash. Wherever tuff is present in the geologic record, geologists can conclude that a massive volcanic eruption took place somewhere nearby.
In the case of Yucca Mountain, the source of the tuff is rhyolitic volcanism that occurred in the region 11.4-15.2 million years ago. However, more recent volcanism has also occurred near Yucca Mountain, including an eruption at Lathrop Wells (about 10 km south-southwest of Yucca Mountain) 80,000 years ago.
Regional tectonics have also played a very important role in the historical and ongoing formation of Yucca Mountain and surrounding landforms. The entire Yucca Mountain region lies on top of three complex tectonic domains. One of these is the Basin and Range Domain, which is characterized by extension that is pulling the crust apart from east to west. This extensional activity began during the Tertiary (65 to 2.6 million years ago) and is still active today.
Potential for Future Seismic and Volcanic Activity
Within Yucca Mountain itself, studies show that regional faulting has been active from the Miocene (23 to 5 million years ago) to the present. The complex network of faults below Yucca Mountain are a result of fracturing as the hot ash flows that make up Yucca Mountain cooled. The mountain is cut many times over by these fractures, adding uncertainty to the stability of the mountain.
Likewise, even though volcanic eruptions have not occurred in the area for 80,000 years, the potential for future volcanic eruptions in the region still exist today, since volcanism in the region is cyclical on the order of every 1 to 4 million years or so. In 2004, the U.S. Court of Appeals ordered the Environmental Protection Agency to establish a new health standard that reflects the time of maximum radioactive contamination. This time may be as much as 1 million years, making a disruptive event that could compromise the safety of a Yucca Mountain nuclear waste storage repository a more likely scenario.
Sources:
- J. S. Stuckless and D. W. O'Leary, "Geology of the Yucca Mountain region," Geological Society of America, Memoir 199, 2007.
- E.I. Smith and D.L. Keenan, "Yucca Mountain Could Face Greater Volcanic Threat," Eos, Transactions, American Geophysical Union, Vol. 86, No. 35, 30 August 2005.
Alexandra Matiella Novak - With a PhD in Geology and expertise in science education, Alexandra is passionate about increasing the public's Earth science literacy.
