A Hydrogeomorphological Study on A Deep-Seated Landslide in the Harihara River Basin, Izumi City, Kagoshima in 1997

Abstract

A deep-seated landslide occurred at Izumi City in northwestern Kagoshima Prefecture on July 10, 1997. Debris flows which followed the landslide killed 21 persons. The purpose of this study is to examine the hydrogeomorphological characteristics of the landslide in the Harihara River basin on the western flank of the old volcano of Mt. Yahazu-lake. We measured the base flow at the observational stations of 14 streams around Mt. Yahazu-lake. The considerable amount of base runoff of the Harihara River originates from the groundwater runoff at the foot of the hillslope where the landslide occurred. The amount of base runoff depends on the spatial distribution of gentle slope and deeply weathered rocks, and the degree of dissection. The stream discharge is an important factor in predicting the potential deep-seated landslide sites.