Mudslides in Japan

Mudslide in Japan

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Introduction

Mudslides occur when sand and earth falls down from the side of hills. In Japan mountains account for over two thirds of the land. and many people have been living with them. They could spend time with rich natural beauty but at the same time, they have sufffered from mudslide many times. In this time, we’re going to see some of the famous mudslide in Japan.

Type of mudslide

Mudslide have three forms, landslide, rockfall, (Database of. 2010)

and debris flow. (saigai no. 2000)

Landslide happens in a place where mudstones, crystaline schists, and solfatalic clay. When it rains violently, or a lot of snow melt, amount of water under the land increase and the land slides slowly. People can see the sign before it happens so they can refuge in advance (Dosha saigai. 2000) .

Rockfall happens like this way. First, rocks on the side of mountain weather, plants grow and a form of the ground changes into crumb structure. Crumb structure can maintain a lot of water and friction between rocks decrease. So when it rains or the weight of the ground increase to some extent, it slide down involving the sand beneath it. Rockfall happens suddenly, so it is very difficult to refuge (Dosha saigai. 2000)

Rock fall on the top of mountains causes debris flow. Earth and sand pour in a river and unite with rocks beneath the river. They get bigger and bigger, and they are faster and faster as they go down and attack town under the mountain (Bousai taisaku. n.d). Most rivers in Japan is steeper than other those of other countries (Nihon to. 2003), debris flow tend to do widespread damage.

Facts

Izu Ōshima

In 2013 October 16th typhoon No.26(http://en.wikipedia.org/wiki/Typhoon_Wipha_(2013)) struck Izu island, and it caused massive mudslide in Ooshima town. It's lowest pressure is 930 hpa and max wind speed was 45m/s (Typhoon Wipha. 2013). 36 residents died, 22 were injured, and 3 are still missing (Heisei 25, 2013).

Mt.Ontake

In 1984 September 14th Otaki earthquake hit Nagano prefecture,Japan. The magnitude was 6.8.It caused a major mudslide south side of Mt.Ontake. Its speed was 80~100km/h(http://www.jma-net.go.jp/matsushiro/learning/seibu）. 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.（https://www.jstage.jst.go.jp/article/sabo1973/48/4/48_4_66/_article ）.

Wakayama Nara

In 2011 September, 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 25th. Typhoon 12 moved very slowly on the sea. The speed was 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(http://www.asahi.com/shimbun/nie/kiji/kiji/20110916.html). Incidentally, it is said that municipal governments in Nara and Wakayama didn’t have enough hazard maps. This is because they need much time to make hazard maps. However, it is difficult to predict where Sinsohokai will occur. Researches are being conducted to predict where Sinsohokai will occur.

Hirosima

In 2010,June,Hirosima had a lot of rain because of the warm atmospherefrom south.This heavy rain caused severe damage like mudslide and river flood.Many places had a lot of rain but especially Shogen(http://en.wikipedia.org/wiki/Sh%C5%8Dbara,_Hiroshima) city had 64 mm rain in a 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 1787 houses were broken. (http://www.bousai.pref.hiroshima.jp/www/contents/1318849847246/index.html)This is manly because the hoses were flooded under the floor. This disaster made us think how we should sheltr in future. According to the victims, it got sudden thunderstorm with strong windy, so some people werre not le to move.The administration have to improve the calculation of weather and make more refuges to prepare for heavy rain. Morever, we ourselves have to study mudslide to survive in disaster.

Measures

The government established a law to prevent sediment disaster in 2000 and partly revise it in 2011, and has been asking people to be careful to cheak the sign and constructing facilities to prevent it(Dosha saigai boushi. 2013). However, people in many places are still exposed to danger of sediment disaster. it is impotant to prepare the facilities ao soon as possible.

Basically, fire fighters help people suffered from sediment disaster, but when it is big, Defence Force of Japan go there to help the victims.

See also

1.Mudflow

2.Flash flood

3.Geography of Japan