Eruption age of the Haruna Futatsudake Pumice (Hr-FP), central Japan, by radiocarbon wiggle matching with special reference to a 14C dataset developed from a Japanese tree

Abstract

Haruna volcano, located in central Japan, erupted the Hr-FA and Hr-FP tephras during a period of several decades around the 6th century. To estimate the precise age of the second eruption, we performed AMS radiocarbon dating on a charred wood trunk (29 rings) collected from a pyroclastic flow deposit of the Hr-FP, and obtained a year range of cal AD 424–444 (2σ) using 14C wiggle matching of seven dates with the IntCal13 dataset. However, this result is approximately 100 years older than the inferred calendar year from Sue pottery and Kofun (ancient tomb mound) chronologies and is also inconsistent with the stratigraphic relation of the Hr-FA and Hr-FP. For the 5−6th centuries when the Hr-FP might have erupted, 14C dating was performed on Japanese trees whose precise chronologies were established dendrochronologically. The 14C ages of the annual rings of these trees showed local offsets about 30 years older than those of IntCal13. This tendency has been observed in several studies on trees in Japan and is consistent with the results from the Japanese cedar tree. As a preliminary study, the Hr-FP data were wiggle matched with the existing local dataset for AD 340–545 obtained from one tree in central Japan. The year of the outermost annual ring of the sample tree collected in the Hr-FP tephra is estimated to be cal AD 538−559 (79.0% probability). This estimated age of the Hr-FP eruption is consistent with the archaeological chronology (Sue pottery and Kofun) and tephrochronology around Haruna volcano.