Earth Planets Space, Vol. 54 (No. 3), pp. 295-301, 2002
Yoshihisa Kawanabe and Genji Saito
Geological Survey of Japan, AIST, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8567, Japan
(Received January 16, 2001; Revised January 25, 2002; Accepted February 3, 2002)
Abstract: Satsuma-Iwojima is a small volcano island located on the northern rim of Kikai caldera to the south of Kyushu, southwest Japan. Observations of new outcrops and 14C dating of the tephra layers have revealed post-caldera activity in the Satsuma-Iwojima area. After the large-scale ignimbrite eruption in 6500 y.B.P., volcanic activity was resumed with rhyolitic activity. At the foot of Iwodake, post-caldera tephra layers are divided into eight units by the development of humic soils. K-In-1 and -2 were formed by basaltic activity with phreatomagmatic eruption around 3900 y.B.P. and had ended by 2200 y.B.P. Other tephra layers (K-Sk-l and K-Sk-u) are rhyolitic ejecta with an increasing proportion of silicified fragments in the younger tephras. On the slope of Iwodake, there are also some pumice fall deposits and pyroclastic flow deposits (K-Iw). From the 14C data of K-Iw, the most recent magmatic activity of Iwodake was around 600-500 y.B.P.