mm mm , ,000 Fig. 1 Locality map of the investigation area NE SW Fi

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1 5 Report on the Landslide Disaster in the Upper Part of the Abukuma River, Fukushima Prefecture, Due to Heavy Rainfall in August 1998 By Takashi INOKUCHI National Research Institute for Earth Science and Disaster Prevention Abstract A large number of landslides occurred in Nishigo and Taishin villages in Fukushima Prefecture on August 27, 1998 as a result of heavy rainfall. Nine persons were killed by the debris from the landslides, and many houses were destroyed. This report describes landslide disasters and the distribution of landslides based on field surveys and aerial photograph interpretation. The geology of this area mainly consists of Shirakawa welded tuff and volcanic sediments. More than one thousand landslides have occurred in this region. These landslides have been classified into 4 types; landslides in the volcanic ash layer on gentle slopes, surface landslides on steep hillside slopes, collapse in weathered welded tuff, and collapse of artificial slopes. Each type of landslide has been described, and the occurrence conditions examined. The problems connected with landslide disaster prevention are also discussed. Key Words : Rainfall disaster, Surfacial landslide, Pyroclastic-flow deposit, Fukushima Prefecture 107

2 mm mm , ,000 Fig. 1 Locality map of the investigation area NE SW Fig. 2 Topographical relief map of the investigation area

Fig.3 Cross section of the investigation area 3.

2 26 90 mm 27 40 mm/h 27 500 mm 1,200 mm 500 mm 4.

3 Fig.3 Cross section of the investigation area mm mm mm/h mm 1,200 mm 500 mm m Fig Schematic geological column. 150 m K m

4 Fig. 5 Precipitation at Mabune and Kumado from August 26th to 31st. m Fig. 7 Landslide distribution around Taiyo-no-Kuni. Fig. 6 Total Precipitation in Fukushima Prefecture from August 26th to September 1st m

5 Photo 1 () An overview of the Karamatsu-sou landslide. Photo 4 Damaged section of Karamatsu-sou. Photo 2 Karamatsu-sou directly hit by landslide debris. Photo 5 An overview of the Keyaki-sou landslide. Photo 3 Destroyed ceiling in Room 5 of Karamatsu-sou m

6 Photo 6 Main source of the Karamatsu-sou landslide m m Fig. 8 Plan view of landslides at Karamatsu-sou. 11 A B 11 D m 25 m m 600 m 3 12 Photo 7 Right side source of the Karamatsu-sou landslide. Fig. 9 Outline sketch of Yoshinome

7 10 Photo 10 Source of the Yoshinome landslide. Photo 8 Flow route of the Karamatsu-sou landslide. 11 Photo 11 Aerial photos of Yoshinome before the disaster. Photo 9 Damaged area of the Yoshinome landslide. 12 Photo 12 Stereo pair photos on landslide at Akanita m

8 10 Fig.10 External view of the landslide at Taishin Junior high school Photo 13 Damaged building of Taishin junior high school km Photo 14 Damaged houses at Kashiwano

9 11 Fig.11 - ( 1/25,000 ) K Y Landslide distribution in the Odakura-Mabune district

10 /25,000 Fig.12 Landslide distribution in the Habuto district. Fig.13 Landslide distribution in the Kumado district

11 , m m m 50 m m cm m m 1.5 m

12 Table 1 Classification of the landslides and their features. 15 Photo 15 Flow type landslide. 14 Fig.14 Schematic sections of the landslide

13 17 Photo 17 Surface failure in weathered tuff. 16 Photo 16 Surface landslide on Shirakawa welded tuff Photo 18 Weathered Shira-kawa welded tuff Photo 19 Landslide on artificial slope of roadside

14 Fig.15 Distribution of gradients on landslide slopes. 16 Fig Extent of damage to human life due to landslide disasters (Revision to Mizutani,1978) , ,

15 No No p p 12) ,000 9,000 8, WEB

16 WEB 136

研究報告B

研究報告B * ** Casualties by the 3 June 1991 pyroclastic flow at Unzen volcano Shinichi SUGIMOTO * and Daisuke NAGAI ** Abstract The 1990-1995 eruption of Unzen volcano, Japan, was characterized by lava dome growth