Debris flow. Mechanics, prediction and countermeasures / Селевые потоки. Механика, предсказание и противодействие

A typical debris flow is a torrential flow of a mixture of water, mud and debris that suddenly pushes ahead with a vanguard of huge, jostling and roaring boulders. It is certainly a very fearful phenomenon that causes disasters, but it is also truly a wonder of nature exciting the curiosity of researchers as to how such a phenomenon can arise. The phenomena themselves had been recognized since ancient times in Japan and given various mnemonic names to make people aware of the dangers. Although there were several detailed witness records around in 1965 when I began working for the Disaster Prevention Research Institute of Kyoto University (hereafter called DPRI), the characteristics and mechanisms of debris flows were still vague, and it was called a ‘phantasmal disaster’.

My first field investigation of such disasters was the ‘Okuetsu torrential rain disaster’ in 1965, which was brought about by a locally concentrated rainfall at the boundary between Fukui and Gifu Prefectures in central Japan. I found many wooden houses were buried up to the second floor by debris that consisted of particles a few tens of centimeters in diameter that had run down the mountain at the back of the town. Yet the frames of those houses were not completely destroyed. This fact told us that the thick deposit of big stones was laid gently. I wondered how such a phenomenon could occur. <...>