Abstract
After heavy rainfall, debris flow induced by flash water took 21 lives at the Harihara river district, Southern Kyushu of Japan, in the midnight of the 10th July 1997. Field investigation, in-situ survey, electrical prospecting, hydro-geological analysis were conducted to find out the essential reason and developped process. Fundamental source behind this disaster was deduced to the hidden fault weakening by confined water consequently. Moving soil mass on down-slope into the agricultural pond had caused flash water and the combined flash flood with soil mass flow acted like debris hydraulic jumps. Conclusions on the sequential processes were drawn as partial failure at the fault, failed material dam or small lake formation, increase in pressure behind, burst of the dammed lake, induced flow of debris and progressive slope failure. Flash water mixed debris hydraulic jumps on the area had devastated the invaluable human lives_ orange fields and farmer hniisines.
