2012 Volume 63 Issue 11-12 Pages 283-289
New accelerator mass spectrometry (AMS) 14C ages from some tephra units of the Younger Oshima Group of Izu-Oshima Volcano were obtained. Age of the caldera forming S2 period are 1780±50yBP and consistent with recent AMS data obtained by other research. The age of S2 period should be revised to be in around 3rd century, about 200 to 300 years older than the previously accepted age from early 1980's. N4 period also shows about 200 to 100 years older than the previous estimated age. The ages of the other periods, N1, Y6, Y5, Y4 and Y2, are consistent with the previously estimated ages by historical records. Since the age of S2 and N4 periods became older, magma discharge rate during S to N period obtained from the tephra volume was smaller than the old estimate, but still two times higher than the magma discharge rate of Y period.
