Igneous events create physical conditions that commonly are beyond the design basis of most engineered systems, with little data available for direct analysis of potentially hazardous scenarios. In addition, interactions with engineered systems can change the character of an igneous event in ways that never occur in nature. These potential changes in process may directly affect the impact of the resulting hazard. In this study, we will examine the potential changes in magma-flow processes that might occur if rising, volatile-poor magma intersects open, subsurface structures such as tunnels or drifts. Examination of decompression processes provides one end-member to the range of models that may need to be considered for potential subsurface hazards associated with basaltic igneous events. Although volatilerich magma decompression may be viewed as a more likely scenario for some basaltic magma systems, examination of the volatile-poor scenario places important constraints on the extent and duration of potential magma flow into underground openings.

The United States has generated ~ 50 000 000 kg of high-level radioactive waste from commercial and defense reactors. The current proposal is to dispose this waste in 300 m-deep tunnels beneath Yucca Mountain, Nevada, USA. The regulatory framework in the United States establishes limits on potential doses to the public for a period of at least 10 ka (NRC, 2001).