Landscape evolution analysis of large scale landslides at Don-Ao Peak, Taiwan

Typhoon Megi (2010) and the co-movement of the concurrent northeast monsoon brought massive rainfall to the Suao area of Yilan County, Taiwan, causing clusters of sediment-related landslide disasters on Provincial Highway No. 9. The most notable of these events was the large-scale landslide on the upper slope at 115.9 km near Don-Ao Peak, which dumped 2.1 million cubic meters of sediment into the streambed. Rainfall runoff turned this into a debris flow forming an alluvial fan at the river mouth. This study analyzed the evolution of landscapes in the area through a field investigation, disaster-causing mechanisms, image interpretation, and airborne LiDAR. Our results indicate that the landslide was associated with its location at a lithological junction as well as local geological structures. Interpretation of micro-photography revealed that the topographical changes in landslide areas in the Dakeng Stream catchment are controlled by the headward development of erosion gullies and the concave shape of the slopes. Previous earthquakes and rainfall exceeding that of a 200-year event were the external precipitating factors.