Geomorphologic characteristics of catastrophic landslides during typhoon Morakot in the Kaoping Watershed, Taiwan

Abstract A high-resolution digital elevation model (DEM) and field investigations are used to analyze the distribution and characteristics of rainfall-induced landslides in the Kaoping watershed of southwest Taiwan during Typhoon Morakot. The heavy rainfall brought by Typhoon Morakot is characterized as high intensity and long duration, with a return period well over 200 years. The landslide distribution correlates well with the heavy rainfall distribution. Heavy rainfall and flood triggered 12,697 landslides, including four giant landslides. The cumulative area of the landslides was 183.1 km 2 . The landslide ratio in four sub-watersheds of the Kaoping watershed exceeded 6.5%. Analysis results indicate that the percentage of the downslope landslide areas is approximately 3.2–10.5 times higher than that of upslope landslide areas owing to serious scour of the riverside. The power–law exponent β for rainfall-induced landslide distribution during Typhoon Morakot is lower ( β  = 1.3–1.4) than that for earthquake-induced landslide distribution in the comparison of self-organized criticality, because the heavy rainfall induced many new landslides at different scales. The Hsiaolin landslide, one of four giant landslides, was a deep-seated, dip-slope landslide with an area of 2.5 km 2 and a volume of 2.7 × 10 7  m 3 . A portion of the sediment slid into the original valley and dammed the Chishan River, while another portion buried Hsiaolin village. Based on the results, the extremely high intensity and long duration of rainfall caused numerous landslides with different scales near the downslope region. We recommend using the detailed topographic changes that occurred during the Hsiaolin landslide to identify and prevent similar deep-seated landslide disasters.

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