How would the eruption of a volcano affect a nearby nuclear power plant (NPP)? Specifically, would the products of a volcanic eruption impact the operation of an NPP located near an erupting volcano? The answer to this question begins with an assessment of the geological phenomena that result from volcanic eruptions. These phenomena are diverse, and include tephra fallout, pyroclastic flows and lahars, among others (Connor et al., Chapter 3, this volume). The effects of these phenomena depend on a host of factors, such as the proximity of the volcano to the NPP, the size and character of the eruption, wind direction and topography around the volcano.

The complexity and uncertainty associated with these phenomena suggest that their potential impacts be assessed probabilistically. One important aspect of probabilistic assessment involves forecasting the timing of eruptions. When will the next eruption occur? Or, phrased another way, how much time must elapse before a volcano no longer has a credible potential for future eruptions? This question is not easily resolved, as volcanoes may go thousands of years, or even tens of thousands of years without erupting. A second aspect of volcanic hazard assessment is estimation of the effects of volcanic eruptions, once they occur. Which areas might be inundated by lahars, or experience tephra fallout? As eruption magnitudes and their effects vary widely, this question must also be answered probabilistically. Admittedly, assessment of the timing and consequences of potential eruptions is a daunting task, requiring site-specific data, a refined understanding of volcanic processes and computational tools to actually estimate probabilities.