UNCOVERING BURIED VOLCANOES: NEW DATA FOR PROBABILISTIC VOLCANIC HAZARD ASSESSMENT AT YUCCA MOUNTAIN
Basaltic volcanism poses a potential hazard to the proposed Yucca Mountain nuclear waste repository because multiple episodes of basaltic volcanism have occurred in the Yucca Mountain region (YMR) in the past 11 Ma. Intervals between eruptive episodes average about 1 Ma. Three episodes have occurred in the Quaternary at approximately 1.1 Ma (5 volcanoes), 350 ka (2 volcanoes), and 80 ka (1 volcano). Because Yucca Mountain lies within the Basin and Range Province, a significant portion of the pre-Quaternary volcanic history of the YMR may be buried in alluvial-filled basins. An exceptionally high-resolution aeromagnetic survey and subsequent drilling program sponsored by the U.S. Department of Energy (DOE) began in 2004 and is gathering data that will enhance understanding of the temporal and spatial patterns of Pliocene and Miocene volcanism in the region (Figure 1). DOE has convened a ten-member expert panel of earth scientists that will use the information gathered to update probabilistic volcanic hazard estimates originally obtained by expert elicitation in 1996. Yucca Mountain is a series of north-trending ridges of eastward-tilted fault blocks that are bounded by north to northeast-trending normal faults. Topographic basins filled with up to 500 m of alluvium surround it to the east, south and west. In the past several decades, nearly 50 holes have been drilled in these basins, mainly for Yucca Mountain Project Site Characterization and the Nye County Early Warning Drilling Program. Several of these drill holes have penetrated relatively deeply buried (300-400 m) Miocene basalt; a Pliocene basalt dated at 3.8 Ma was encountered at a relatively shallow depth (100 m) in the northern Amargosa Desert (Anomaly B in Figure 1). The current drilling program is the first to specifically target and characterize buried basalt. Based on the new aeromagnetic survey and previous air and ground magnetic surveys (Connor et al. 2000; O'Leary et al. 2002), at least eight drill holes are planned with the goal of sampling each geographic subpopulation of magnetic anomalies in the region (Figure 1). This will result in a more complete characterization of the location, age, volume and composition of buried basaltic features for the purpose of updating the volcanic hazard assessment. Smith and Keenan (2005) suggested that volcanic hazard estimates might be 1-2 orders of magnitude higher than estimated by the DOE expert elicitation in 1996, based on (1) a proposed relationship between recurrence rates in the YMR and the Reveille-Lunar Crater volcanic field to the north, and (2) the implication that a number of so-far-undiscovered buried volcanoes would have a significant impact on hazard estimates. This article presents the new aeromagnetic data and an interpretation of the data that suggests magnetic anomalies nearest the proposed repository site represent buried Miocene basalt that will likely have only a minor impact on the volcanic hazard.
- Research Organization:
- Office of Scientific and Technical Information (OSTI), Oak Ridge, TN (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- NA
- OSTI ID:
- 861074
- Report Number(s):
- NA; MOL.20051118.0029 DC#46163; TRN: US0600597
- Country of Publication:
- United States
- Language:
- English
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