和歌山県那智川流域における土石流の発生頻度

抄録

Debris flow deposits consist of poorly sorted gravel beds composed of granite porphyry are distributed along the Nachi River, Wakayama Prefecture. In order to determine the age of sediment deposition, we carried out of calendar calibrated ¹⁴C dating using 22 wooden fragments collected from debris flow deposits. ¹⁴C dates indicate that 10 depositional events of debris flow during the past 14,000 years. These debris flow deposits derive from heavy rainfall events because ¹⁴C dates are inconsistent with the age of large historical earthquake along the Nankai-trough. Frequency of large-scale debris flow caused by heavy rainfall in the Nachi River is estimated 10³ years during the past 14,000 years.