Thickness distribution of pyroclastic fall layers on outer slopes of the caldera rim, Izu Oshima Volcano

Abstract

  Heavy rainfall associated with the typhoon T1326 (Wipha) of 2013 triggered large-scale shallow landslides and long-runout of the displaced mass at outer slopes of the caldera rim, resulting severe disaster at Motomachi district, Izu Oshima Island. To prevent such disasters in volcano regions, thickness distributions of pyroclastic fall layers should be known as potential source of landslide materials. Thickness distribution of alternated tephra and loess layers on slopes were estimated based on data from the study on eruptive history of the Izu Oshima Volcano (Koyama and Hayakawa, 1996) using a kriging method, and compared with actual values measured in field. Results showed that the measured tephra thickness and accumulated thickness varied from 0.2 to 2.2 times and from 0.8 to 1.9 times of the estimation, despite the similarity in fall out amount and stratigraphy of tephra (within the Okane-zawa Catchment : 1.2km²)