Paleointensity high at 9000 years ago from volcanic rocks in Japan

Abstract

Six paleointensities were determined from young lava flows of Fuji and Oshima Volcanoes whose ages are around 8000 to 15000 years B.P. Two lava flows which have well‐defined ages at 8970±390 years B.P. and 9260±430 years B.P. give large paleointensities of 67±12 and 65±6 μT, respectively. Another lava flow of less accurate age also gives large paleointensity of 63±6 μT. The new paleointensity data are consistent with the trend of averaged paleointensity variation in Japan for the last 9000 years. They form a peak of paleointensity high at around 9000 years B.P. comparable to the well‐documented one at 2000 years B.P. This suggests that there exists a dominant component with a characteristic period of about 7000 years in paleointensity variation. Large paleointensity at about 8000–10000 years ago is also reported in France and Iceland. Paleointensity variation averaged every 1000 years for the last 14000 years is quite similar in Europe and Japan. The sine‐curve‐like variation of paleointensity observed in both Europe and Japan probably reflects the nature of the dipole moment if we consider much difference of longitude between the two regions.