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  • Three radiometric methods have been used to date Quaternary tephra: fission-track (F-T), K-Ar, and radiocarbon (C-14). The fission-track and K-Ar methods provide direct ages for the tephra because they date phenocrysts from the source magma
  • that were deposited by the eruption cloud. Radiocarbon dating provides only indirect ages because the carbon used in this method comes from material, such as pre-existing wood, included in the tephra during deposition or collected from underlying
  • 1981