Case Study on the Kokkawa Landslide Caused by Snowmelt
This paper presents comprehensive study of the process and mechanism of the 7th March 2012 Kokkawa landslide in Japan. The landslide has the following dimensions; average width of 150 m, maximum length of about 500 m. The depth of the sliding surfce is about 20 m. The volume of the sliding soil mass is estimated to be 750,000 m3. Although no one was killed or injured, several house were completely destroyed by the sliding soil mass. In addition, a lot of inhabitants of neighbouring houses had to be evacuated. The Kokkawa landslide occurred in Joetsu City, which is located in the southwestern part of Niigata Prefecture. Many deep-seated landslide events have been recorded in the past in Joetsu City area. The area is also characterized by long and heavy bouts of hazardous snow falls. A lot of snow accumulation was observed in the vicinity of the landslide area during winter season. Clearly the landslide was triggered by snowmelt. The soil layer above the geological formation border probably contained high amount of water due to antecedent snowmelt before the occurrence of the landslide. It was remarkably observed that the sliding soil mass has long travel distance and high velocity at the early stage of the movement.
KeywordsSnowmelt Travel distance Drainage Topography Landslide hazard assessment
The authors are thankful to the Department of Torrent and Erosion Control of Niigata Prefectural Government for practical arrangement for field visit and also for provision of technical materials like aerial photographs and topographical maps.