### Estimate of tephra accumulation probabilities for the U.S. Department of Energy's Hanford Site, Washington

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#### Abstract

^{3}(bulk volume) or more of tephra, (2) the probability that the wind will be blowing toward the Hanford Site, and (3) the probability that tephra accumulations will equal or exceed the given thickness at a given distance. Mount St. Helens, which lies about 200 km upwind from the Hanford Site, has been the most prolific source of tephra fallout among Cascade volcanoes in the recent geologic past and its annual eruption probability based on this record (0.008) dominates assessment of future tephra falls at the site. The probability that the prevailing wind blows toward Hanford from Mount St. Helens is 0.180. We estimate exceedance probabilities of various thicknesses of tephra fallout from an analysis of 14 eruptions of the size expectable from Mount St. Helens and for which we have measurements of tephra fallout at 200 km. The result is that the estimated thickness of tephra accumulation that has an annual probability of 1 in 10,000 of being equaled or exceeded is about 10 centimeters. It is likely that this thickness is a maximum estimate because we used conservative estimates of eruption and wind probabilities and because the 14 deposits we used probably provide an over-estimate. The use of deposits in this analysis that were mostly compacted by the time they were studied and measured implies that the bulk density of the tephra fallout we consider here is in the range of 1,000-1,250 kg/m

^{3}. The load of 10 cm of such tephra fallout on a flat surface would therefore be in the range of 100-125 kg/m

^{2}; addition of water from rainfall or snowmelt would provide additional load.

Publication type | Report |
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Publication Subtype | USGS Numbered Series |

Title | Estimate of tephra accumulation probabilities for the U.S. Department of Energy's Hanford Site, Washington |

Series title | Open-File Report |

Series number | 2011-1064 |

DOI | 10.3133/ofr20111064 |

Year Published | 2011 |

Language | English |

Publisher | U.S. Geological Survey |

Publisher location | Reston, VA |

Contributing office(s) | Volcano Science Center |

Description | iv, 13 p.; Appendices |

Online Only (Y/N) | Y |

Additional Online Files (Y/N) | N |

Google Analytic Metrics | Metrics page |