Journal of Natural Disaster Science
Journal of Natural Disaster Science Vol.20, No.2, 1998
A Study of the Change from a Landslide to Debris Flow at Harihara, Izumi City, Southern Kyushu
(Received 8 October, 1998 and in revised form 22 February, 1999)
Abstract
A debris flow disaster due to heavy rainfall during the latter half of the rainy season occurred on July 10, 1997, causing the death of 21 people at Harihara, Izumi City, Kagoshima Prefecture in southern Kyushu. The debris flow was induced by a large scale landslide on the middle reaches of a small catchment, the Harihara River. The process of change from landslide to debris flow seems to have been completed within a short period. The landslide was of the deep-seated rotational type with a deep slip surface of approximately 30 m maximum depth and a volume of about 130,000 cubic meters. The landslide may have been caused by a rise in the groundwater level in association with heavy rainfall. The lower part of the hillslope with a slope angle of 20 to 30 degrees, the deeply weathered volcanic rocks, lineament, stream discharge into the river basin, and spring water discharge from groundwater in the Mt. Yahazu volcano may be effective indicators for predicting potential sites of deep-seated landslides.
Key words
Debris flow disaster, deep-seated landslide, heavy rainfall, groundwater, Izumi City