A mudslide or mudflow occurs when rocks, sand and earth fall down from the side of hills due to rain or snow. In Japan mountains account for over two thirds of the land, and therefore there is a risk of mudslides.[1]
Facts
Mount Ontake
On September 14 1984 Otaki earthquake hit Nagano prefecture, Japan. The magnitude was 6.8 and it caused a major mudslide south side of Mt.Ontake. Its speed was 80~100 km/h.[2] Besides the earthquake, the heavy rain that had continued for several days before the earthquake was another factor of the mudslide. The slide is called “Ontake Kuzure.” It took the lives of 29 people. After the disaster, the barriers against mudslide were made in nine places at the hill foot of Mt. Ontake.[3]
Wakayama, Nara
In September 2011, typhoon No.12 hit Japan. Because of it, it rained very heavily in the Kii Peninsula. There are many mountains in the Kii Peninsula, and usually it rains heavily there. Typhoon 12 occurred on August 25. Typhoon 12 moved very slowly on the sea, at speeds of 15 km/h at most. So, the south wet air stayed in one area for a long time. Then it kept raining at the slope of mountains. Therefore, in Wakayama and Nara, the mudslide occurred. This mudslide is called “Sinsohokai”. If Sinsohokai occurs, very deep ground on mountains is carried away. It means that not only soil but also bedrock in the ground collapses. One of reasons why Sinsohokai occurred is that it rained for a long time, and the ground soaked up much water. In this case, houses were covered with earth and sand from the mudslide. So, the residents suffered heavy damage, and many people died [4]
Hiroshima
In June 2010, Hirosima had a lot of rain because of the warm atmosphere from the south. This heavy rain caused severe damage including mudslides and river floods. Many places had a lot of rain but especially Shōbara city had 64 mm rain in an hour. Hirosima had 30~50 mm at 12th, 20~40mm at 13th, 20~50mm at 14th, which was heavy rain. In this disaster, 5 people were killed and 6 people were injured, and 1,787 houses were broken.[5]
^Naganoken Seibu Jishin (The earthquake which hit Nagano prefecture). Matsuhiro Seismological Observatory. Retrieved:www.jma-net.go.jp/matsushiro/learning/seibu.html [July/20,2014]
