Journal of the Japan Society of Erosion Control Engineering,
Vol.56,No.5,2004
The characteristics of 1926 volcanic mudflow at Mount Tokachi, the evidences of eyewitnesses and examination of the deposited materials
Tomoyuki NANRI, Motohiro KUREBAYASHI, Takayuki YAMAHIRO, Tetsuya NATORI, Yukimasa KANEKO, Kouji HASEGAWA, Tohru ARAYA
Abstract
Large]scale mudflow occurred as an aftermath of the eruption of Mount Tokachi Volcano on May1926, and killed 137 residents in Kami]Furano town of central Hokkaido. The flowing conditions of the mudflow were investigated by interviewing survived eyewitnesses and examining remnant of the mudflow deposits, concentrating on flow velocity and depth, condition of scouring and deposition, houses destruction, and deposited materials variation according to the sites. Surveying the mudflow descent conditions, it was divided into three types as follow: Flow T ,with the velocity from 11 to 17m/s, the depth from 4 to 6m and about 1000KN/m fluid dynamic force, was capable of serious destruction of houses at the foundation, Flow U ,with the velocity from 5 to 9m/s, the depth from 2 to 4m and more than 100KN/m fluid dynamic force, was capable of causing a heavy collapse of houses, and Flow V ,whose velocity, depth and fluid dynamic force were smaller than U ,was capable of slightly destroying houses and burying them. Studying the mudflow characteristics, the flow condition was thought to be flood]like and easily flowing with huge amount of sediment, great flow velocity and density suggesting high intensity resulting to massive devastation.
Key words:volcanic mudflow, interviewing eyewitness, remnant of the mudflow, deposited grain size distribution, volcanic mudflow behavior
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