Abstract
Soil samples were collected from the upper layers of two Unzen volcano Scientific Drilling Project boreholes and dated by radiocarbon using accelerator mass spectrometry (AMS). The humic soils underlying volcanic related lahar flow deposits at a depth of 56.42 m of the USDP-1 borehole gave a 14 C age of 18.8 ka BP, suggesting that the accumulation of the lahar flow deposits was caused by the Kureishibaru pyroclastic eruption (19 ka BP) dated at the surface. The humic soils underlying a pyroclastic flow deposit at depths of 71.60–71.90 m of the USDP-2 borehole gave 14 C ages of 27.5 and 29.3 ka BP at the top and bottom layers, respectively. This reveals that the initial activity of Fugendake volcano occurred around 27 ka BP and the collapse of Myokendake volcano around 29 ka BP.
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