Geological factors for hazardous debris flows in Hoser, central Taiwan

By means of an onsite investigation, the largest debris flow in Taiwan's hi story is analyzed in this paper. A heavy rainfall of 1,748 mm/day occurred during typhoon Herb in the Hoser area at the end of July 1996. Aerial photo graphic assessment and observations of geological and geomorphological feat ures have contributed to our understanding of this massive destruction. Mec hanisms of the hazardous debris flow are explored and discussed. Data revea led that the rock discontinuities were a major factor in the voluminous loo se materials in the debris flows. The heavy and rapid rainfall instantly tr ansported massive amounts of debris flow materials into the center, and the n quickly funneled them to the lower parts of gullies. The heavy slurry bec ame an effective cutting device to erode the side walls and move large quan tities of the debris materials, to the end of the gullies.