Radiocarbon dating of the last volcanic eruption of the Ciomadul volcano, Southest Carpathians

Complete text of publication follows. The last volcanic eruption in the Carpathian-Pannonian Region occurred within the Ciomadul volcano, Southeast Carpathians. It is a lava dome complex active for about 900 ka. Following the effusive activity, at least two major explosive volcanic eruptions occurred forming two craters (Mohos and St. Anna). These eruptions resulted in pumiceous pyroclastic fall and flow deposits. In order to understand the behavior of this volcano and evaluate the possible renewal of the volcanic eruption, it is crucial to constrain the length of the active and repose periods and know the date of the last eruption. The former K/Ar and radiocarbon data are controversial and give only a rough estimate for the active phases. The age data for the last eruption is in the range from 10000 and 40000. In this study, we focus on the time of the last volcanic eruptions. We analyzed charcoal fragments found in pumiceous pyroclastic flow deposits from two localities. C-14 dating from the first locality (Bx) was executed by GPC technique in the ATOMKI, and the following five dating (one repeated dating of the ATOMKI sample, with excellent match; one resampled charcoal from the first locality, and one sample from a second locality (Tf), and dating of NaOH-soluble fractions coming from sample prep for all the three charcoal samples) in NSF Lab in Tucson, AZ by AMS technique. The new radiocarbon data provided valuable information on the behaviour of the Ciomadul volcano and help to constrain the time of the last eruption of the volcano. The main conclusions are the following: 1. The last volcanic eruption occurred at about 27000 BP. 2. The product of the youngest eruption is exposed at the southern margin of the volcano (Bx locality) and not at west (Tf locality) as was previously thought. 3. A striking new result is that there were at least two major explosive eruptions, not a single one, related to the formation of the St. Anna crater. The youngest one followed another subplinian eruption after about 10 ka quiescence period. 4. Further dating for the time of the older eruptions is crucial to understand the nature of the volcano and to evaluate the characteristic repose time of Ciomadul. These data are consistent with the different composition of the volcanic products from the two localities. Acknowledgements This study is part of the research project supported by the OTKA grant K68587.