Abstract
A local heavy rainfall struck central area of Niigata Prefecture on 13th July 2004. It is reported that more than two thousands of slope movements occurred on the hill slopes and in the mountainous areas where the heavy rainfall concentrated. The geological background of the area consists of Tertiary mudstone and sandstone. Most of slope movements are shallow slope failure type in small dimension. However, not a few landslides and debris flows which displaced soil mass of more than several ten thousands cubic meters have occurred. Two people were killed by slope failures. Although the number of the victims is not high, tremendous volume of debris and sediment moved down and caused destruction of houses and blockage of roads. It should be noticed that evacuation maneuvers have been appropriately managed and it caused minimum victims comparing with a dimension of total slope movements. A large amount of unstable debris and sediment are still remaining in most of landslide areas and debris flow deposition areas. It is necessary to evaluate the volume and danger degree of such unstable materials in order to mitigate successional disasters in the near future.
