How 210Pb dating gives information about volcanic radionuclides

In lake sediments from the Taupo Volcanic Zone, the 1886 Tarawera tephra is often observed. The tephra contains unsupported 210Pb which corresponds to its stratigraphic age, and shows that the 210Pb has been adsorbed in its passage through the air, but not from the volatiles in the volcano itself which would be expected to contain the radionuclide. It is shown that only a small portion of the available 210Pb in normal air was scavenged by the tephra. Sedimentation rates derived using the tephra were similar to those from 210Pb dating. Some lakes showed excess 210Pb inventories, ascribed to lake-bed geothermal activity. Contrary to expectation of increased erosion following deposition of an ash layer, sedimentation rates were less. (author). 10 refs., 2 figs