Abstract
Nineteen radiocarbon 14C age data of Shikotsu Pumice Fall (Spfa) and Shikotsu Pumice Flow (Spfl) deposits are newly obtained and ages of volcanic activity of Shikotsu Volcano are re-examined in this paper. Spfa consists of ten pumice and/or scoria fall deposits (Spfa1 to Spfa10) with intercalating loams. Their eruption and sedimentation ages range for about 10,000 years. Spfl is made up of pumice and ash flow deposits. According to field observations, there is no time interval between Spfl and Spfa1. Time intervals are found between Spfa2 and Spfa3-6 and also between Spfa3-6 and Spfa7-10. The eruption and sedimentation ages of Shikotsu Volcano are estimated as follows. Spfl and Spfa1 are 41,000y.B.P., Spfa2 is 42,000y.B.P. to 44,000y.B.P., Spfa3-6 is 43,000y.B.P. to 46,000y.B.P., including a datum of 45,500y.B.P. for Spfa3, and Spfa7-10 is 46,000y.B.P. to 50,000y.B.P. These ages indicate almost 10,000 years older than so far available data. It is necessary to reconsider the geological expressions of Shikotsu volcanic activity.
