Assessment of Potential Volcanic Hazards: Pasco Basin, Washington

摘要

A volcanic hazard assessment was performed for three time intervals by considering: (1) the potential for renewed volcanism from three source areas (the Cascade Range, the Columbia Plateau, and the Basin and Range Provinces); and (2) the potential effects of future volcanic events on a 2- x 3-km repository sited 2 km beneath the surface of the Pasco Basin. Important parameters used in the assessment include recurrence intervals, geologic conditional probabilities, and expected outcomes. These parameters were characterized for each of the three potential source areas. To enhance the determination of these parameters, basaltic volcanism on the Columbia Plateau is compared with two other flood basalt sequences (Karroo and Deccan) to gain insight on recurrence intervals and the character of eruptions which may occur in the future. The potential for renewed volcanism from each of the three source areas is determined using the estimated eruption rates. Event networks are used to show the logical sequence of events that would follow if volcanism were to recur in any of the source areas analyzed. The networks include all likely events that could credibly occur subsequent to renewed volcanism. Of all potential events analyzed, only a few are considered hazardous to a potential repository (e.g., volcanically induced flooding, ash or lava flows, thick air fall tephra); still fewer are of critical concern (e.g., breach of the repository by a dike). To assess relative likelihood and occurrence of the outcome events, their probabilities were calculated assuming the regional volcanism follows a Poisson distribution. The resulting occurrence probabilities for hazardous events owing to volcanism are calculated. (ERA citation 07:053004)