Eruption Probabilities for the Lassen Volcanic Center and Regional Volcanism, Northern California, and Probabilities for Large Explosive Eruptions in the Cascade Range Scientific Investigations Report 2012–5176–B U.S. Department of the Interior U.S. Geological Survey 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 Scientific Investigations Report 2012–5176-B U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior KEN SALAZAR, Secretary U.S. Geological Survey Marcia K. McNutt, Director U.S. Geological Survey, Reston, Virginia: 2012 For product and ordering information: World Wide Web: http://www.usgs.gov/pubprod Telephone: 1-888-ASK-USGS For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment: World Wide Web: http://www.usgs.gov Telephone: 1-888-ASK-USGS This report and any updates to it are available online at: http://pubs.usgs.gov/sir/2012/5176/b/ Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted material contained within this report. 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/) iii Contents Abstract ..........................................................................................................................................................1 Introduction ....................................................................................................................................................1 Chronologies ..................................................................................................................................................2 Probabilities ....................................................................................................................................................4 Lassen Volcanic Center .......................................................................................................................7 Regional Mafic Vents .........................................................................................................................12 Probability of Large Explosive Eruptions in the Cascades ....................................................................16 Conclusion.....................................................................................................................................................19 Acknowledgements .....................................................................................................................................21 References Cited..........................................................................................................................................21 Figures 1. Time history of eruptive events for the Lassen Volcanic Center ..................................................4 2. Time history of cumulative area and volume of erupted lava for the Lassen Volcanic Center. ......... 5 3. Time history of events for eruptive sequences of regional mafic vents for models I and II ..............8 4. Time history of all eruptive events for regional mafic vents for models I and II ........................8 5. Time history of cumulative area of erupted material for regional mafic vents for models I and II ...........................................................................................................................9 6. Time history of cumulative volume of erupted material for regional mafic vents for models I and II ...........................................................................................................................9 7. Probability that an eruption will occur in a time less than a given time interval between eruptions ........................................................................................................................10 8. Conditional probability that an eruption will occur at the Lassen Volcanic Center in the next year, given a time since the last eruption .................................................................10 9. Probability that an eruption in the Lassen Volcanic Center or from a regional mafic vent will have a volume or area greater than a given value ..........................11 10. Probability that an eruption will occur at a regional mafic vent in a time less than a given time interval after the previous eruption ........................................................12 11. One minus the probability that an eruption will occur at a regional mafic vent in a time less than a given time interval between eruptions .....................................................13 12. Transformed (Weibull) plot of the probability that an eruption will occur in a time less than a given time interval after the previous eruption .........................................14 13. Conditional probability that an eruption will occur from a regional mafic vent in the next year, given a time since the last eruption .................................................................15 14. Cumulative number of eruptions versus age for all the data in table 4 with volumes >≈5 km3 and also for only those eruptions with volumes ≥10 km3 .....................17 15. Cumulative number of eruptions versus age for volumes >≈5 km3 for the past 15 thousand years.....................................................................................................17 16. Probability that an eruption will occur in a time less than a given time interval since the previous eruption .................................................................................................................20 17. Probability of an eruption in the next year for various events in the Cascades. .....................20 iv Tables 1. Chronology of eruptions less than 100,000 years old in the Lassen Volcanic Center .........................3 2. Chronology of eruptions less than 100,000 years old for the mafic vents in the surrounding area of the Lassen segment of the Cascade Range ............................................6 3. Parameter values for the Weibull distribution for the straight-line solution and root solution for the eruption chronologies for models I and II for the regional mafic vents .......................15 4. Compilation of data on large explosive eruptions in the past 1.2 million years in the Cascade volcanic arc ........................................................................................................18 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 Abstract Introduction Chronologies for eruptive activity of the Lassen The Lassen Volcanic Center and its predecessors are Volcanic Center and for eruptions from the regional mafic distinguished from the surrounding regional mafic volcanism in vents in the surrounding area of the Lassen segment of the northern California by their greater longevity, larger volumes, Cascade Range are here used to estimate probabilities of and broader range of silica concentrations (Clynne and Muffler, future eruptions. For the regional mafic volcanism, the ages 2010). Clynne and others (2012) provide chronologies for eruptive of many vents are known only within broad ranges, and activity at the Lassen Volcanic Center and for eruptions from the two models are developed that should bracket the actual regional mafic vents in the surrounding area of the Lassen segment eruptive ages. These chronologies are used with exponential, of the Cascade Range for the past 100,000 years (for geographic Weibull, and mixed-exponential probability distributions extent covered, see Clynne and others, 2012, fig. 4). We use to match the data for time intervals between eruptions. For these chronologies to calculate probabilities of future eruptions. the Lassen Volcanic Center, the probability of an eruption Areas and volumes of lava flows and domes have been estimated in the next year is 1.4×10-4 for the exponential distribution on the basis of geologic mapping (Clynne and Muffler, 2010; and 2.3×10-4 for the mixed exponential distribution. For M.A. Clynne and L.J.P. Muffler, written commun., 2010), and the regional mafic vents, the exponential distribution gives these values are presented in time histories and used to calculate a probability of an eruption in the next year of 6.5×10-4, probabilities of sizes of eruptions. but the mixed exponential distribution indicates that the An underlying assumption of past U.S. Geological Survey current probability, 12,000 years after the last event, could (USGS) volcano hazards assessments for Cascade Range be significantly lower. For the exponential distribution, the volcanoes in Oregon and Washington has been that the probability highest probability is for an eruption from