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U.S. Geological Survey Scientific Investigations Report 2012–5176–B

Eruption Probabilities for the Lassen Volcanic Center and Regional Volcanism, Northern California, and Probabilities for Large Explosive Eruptions in the Cascade Range

By Manuel Nathenson, Michael A. Clynne, and L.J. Patrick Muffler

Thumbnail of and link to report PDF (1.1 MB)Abstract

Chronologies for eruptive activity of the Lassen Volcanic Center and for eruptions from the regional mafic vents in the surrounding area of the Lassen segment of the Cascade Range are here used to estimate probabilities of future eruptions. For the regional mafic volcanism, the ages of many vents are known only within broad ranges, and two models are developed that should bracket the actual eruptive ages. These chronologies are used with exponential, Weibull, and mixed-exponential probability distributions to match the data for time intervals between eruptions. For the Lassen Volcanic Center, the probability of an eruption in the next year is 1.4x10-4 for the exponential distribution and 2.3x10-4 for the mixed exponential distribution. For the regional mafic vents, the exponential distribution gives a probability of an eruption in the next year of 6.5x10-4, but the mixed exponential distribution indicates that the current probability, 12,000 years after the last event, could be significantly lower. For the exponential distribution, the highest probability is for an eruption from a regional mafic vent. Data on areas and volumes of lava flows and domes of the Lassen Volcanic Center and of eruptions from the regional mafic vents provide constraints on the probable sizes of future eruptions. Probabilities of lava-flow coverage are similar for the Lassen Volcanic Center and for regional mafic vents, whereas the probable eruptive volumes for the mafic vents are generally smaller.

Data have been compiled for large explosive eruptions (>≈ 5 km3 in deposit volume) in the Cascade Range during the past 1.2 m.y. in order to estimate probabilities of eruption. For erupted volumes >≈5 km3, the rate of occurrence since 13.6 ka is much higher than for the entire period, and we use these data to calculate the annual probability of a large eruption at 4.6x10-4. For erupted volumes ≥10 km3, the rate of occurrence has been reasonably constant from 630 ka to the present, giving more confidence in the estimate, and we use those data to calculate the annual probability of a large eruption in the next year at 1.4x10-5.

         See also:
  • SIR 2012–5176–A, Volcano Hazards Assessment for the Lassen Region, Northern California
  • This report is available only on the Web.

For additional information:
Contact CalVO
Volcano Science Center, California Volcano Observatory
U.S. Geological Survey
345 Middlefield Road, MS 910
Menlo Park, CA 94025
http://volcanoes.usgs.gov/observatories/calvo/

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Suggested citation:

Nathenson, M., Clynne, M.A, and Muffler, L.J.P., 2012, Eruption probabilities for the Lassen Volcanic Center and regional volcanism, northern California, and probabilities for large explosive eruptions in the Cascade Range: U.S. Geological Survey Scientific Investigations Report 2012–5176–B, 23 p. (Available at http://pubs.usgs.gov/sir/2012/5176/b/.)



Contents

Abstract

Introduction

Chronologies

Probabilities

Probability of Large Explosive Eruptions in the Cascades

Conclusion

Acknowledgements

References Cited


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