Large-scale volcanic slope failures occurred at 1.1 ka in the east of Mt. Fuji, Japan

Abstract

The Omika Debris Avalanche Deposit is exposed along the construction site of the Shin-Tomei Highway east of Mt. Fuji. This deposit is 9.3×10⁶ m³ in volume, and consists of slumped S-5 to S-22 scoria fall deposits (Fuji volcanic products) on the steep slope of Mt. Obora. This avalanche occurred between AD 848 and the middle of the 10th century, as inferred from the stratigraphy of the underlying Kozu-Tenjosan tephra and a new ¹⁴C age for the overlying soil. The AD 887 Nin'na earthquake, which was a great subduction earthquake along the Nankai Trough, took place during this period and presumably triggered the Omika Debris Avalanche.