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U. S. Geological Survey, Reston, Virginia, radiocarbon dates XV; Mauna Loa and Kilauea volcanoes, Hawaii.

M L Kelley, E C Spiker, P W Lipman, J P Lockwood, R T Holcomb, M Rubin

Abstract


Ninety-six new 14C dates are reported for carbonized roots and other plant material collected from beneath prehistoric lava flows and ash deposits from Mauna Loa (ML) and Kilauea volcanoes. Before 1976, only 10 flows from these volcanoes had been dated by radiocarbon methods. Collection of dateable material has been facilitated by an improved understanding of the conditions of charcoal formation and preservation beneath basaltic lavas (Lockwood & Lipman, 1979). The new dates indicate that the brief recorded history of ML eruptive activity, beginning about 1840, has documented an exceptionally active period. For example, 5 flows from the SW rift zone of ML reached the ocean between 1868 and 1950, but in the preceding 500 yr only 3 flows appear to have reached the sea. In contrast, Kilauea flank eruptions along the E rift zone appear to have been more extensive before approximately 200 yr ago than since that time. The available radiocarbon dates also show that the surface flows on ML tend to be older than those of Kilauea. Flows several thousand yr old are common on ML, but flows more than a few hundred yr old are rare on Kilauea. Samples are counted in the form of acetylene gas, as previously, and ages are expressed in radiocarbon yr based on the Libby half-life, 5568 + or - 30 yr, referenced to the yr AD 1950. The dates are not corrected for isotopic fractionation or natural 14C variations. Errors are stated in terms of one standard deviation based only on the counting statistics and not the analysis of replicate samples from the field. The counting error does not include variable factors such as contamination and isotopic fractionation, which if considered, may increase the confidence interval in some cases by a factor of 2 or 3. Unless otherwise noted, collectors of all samples are members of the US Geological Survey.

Keywords


basaltic composition;Hawaii County Hawaii;Hawaii Island;Kilauea;Mauna Loa;Hawaii;East Pacific Ocean Islands;Oceania;Polynesia;lava flows;Holocene;United States;Cenozoic;charcoal;Quaternary;geochronology;C 14;carbon;dates;isotopes;radioactive isotopes;absolute age;fractionation

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