Journal of Natural Disaster Science

SLOPE FAILURE IN A HYDROTHERMAL ALTERATION AREA: A CASE STUDY ON THE IZU PENINSULA, CENTRAL JAPAN

Minoru UTADA
Associate Professor, The University Museum, The University of Tokyo

(Received 1 May, 1989 and in revised form 9 August, 1989)

Abstract

Two heavy rainfalls in August of 1982 caused about two thousand failed slopes that seriously damaged to transportation networks on the Izu Peninsula in central Japan. About half of the failed slopes took place in hydrothermal alteration areas. Details of the mode, volume, and frequency of slope failure differed among the alteration zones. In general, slope failure was more frequent in low grade zones such as those made up of smectite and halloysite, probably because of the extreme decrease of the strength of the parent rock in the course of alteration. The change in rock strength seems to be related to the amount, mode of occurrence and mineralogical properties of the authigenic minerals.

Key words

slope failure, rock alteration, rock strength, hydrothermal alteration, rainfall