Recent rainfall-induced landslides and debris flow in northern Taiwan

This paper discusses the factors initiating landslides and a large-scale debris flow in the Chonho area of Taipei County, northern Taiwan, which resulted from heavy rainfall during Typhoon Xangsane in November 2000. The morphology and triggering mechanism of the landslides and the debris flow were investigated using aerial photographs taken over the past 20 years, field measurement of channel cross-sections, laboratory assessment of slope material properties, and slope stability analysis. A large landslide that occurred in the source area was the initial source of material for the debris flow. The majority of the landslide debris entered the main stream, where it mixed with water and became a debris flow. Eroding the sidewalls of the stream, the debris flow entrained additional material and traveled downstream into Chonho Village. Our findings indicate that the November 2000 landslides and the debris flow were strongly influenced by the physical properties of the underlying pyroclastic substrate and the pattern of bedrock discontinuities within the valleys.