四国山地から見出されたテフラに基づく山地斜面の長期安定性

Formative processes of mountain slope in Shikoku Mountains are discussed based on tephrochronology. We
carried out identification of tephra layers in colluvial deposits at mountain slope, Shikoku Mountains, Tokushima
Prefecture. These tephras named locally Ohyohchi, Nakaue-1 and -2 tephras. Ohyohchi tephra and Nakaue-1
tephra are correlative with AT tephra from South Kyushu, and Nakaue-2 tephra is correlative with K-Ah tephra
from South Kyushu, in terms of the similarities of petrography, refractive index of volcanic glass. The
occurrence of these tephra layers shows that K-Ah tephra overlies colluvial deposits including AT tephra. Thus,
recurrence interval of slope failure was estimated to be more than ten thousand years.