[H-DS09] Landslides and related phenomena

[HDS09-10] A field example of flexural toppling at Song-Mao Village in central Taiwan

*Ching-Ying Tsou¹, Osamu Yokoyama², Fumitoshi Imaizumi³, Hsi-Hung Lin⁴, Yu-Chung Hsieh⁴, Mien-Ming Chen⁴, Masahiro Chigira⁵, Chun-Yi Wu⁶, Su-Chin Chen⁶ (1.Faculty of Agriculture and Life Science, Hirosaki University, 2.Japan Conservation Engineers Co., Ltd., 3.Faculty of Agriculture, Shizuoka University, 4.Central Geological Survey, Taiwan, 5.Disaster Prevention Research Institute, Kyoto University, 6.College of Agriculture and Natural Resources, National Chung Hsing University)

Keywords: flexural toppling, gravitational slope deformation, Taiwan

Landslides can pose a serious risk to the urban environment and to line infrastructures in many humid, tectonically active regions. In this study, geological and geomorphological surveys were conducted at Song-Mao Village in central Taiwan, whereas the area has been affected by deep-seated gravitational slope deformation in the long-term. Aligned at the similar elevations at 1600 m a.s.l. along both sides of the Dajia River, a series of the flat ledge is distributed and ledges on opposite sides of the river sometimes interlock, suggesting that they are the remnants of ridges above slip-off slopes of an old meandering river. The study area is located at one of the flat ledges with two free surfaces (NE-facing and W-facing) along the Dajia River. The bedrock on the upper slope consists of slate striking NE-SW with steeply dipping cleavage at 85° to SE and the lower slope consists of alternating beds of sandstone and slate striking NE-SW and dipping 70° to 85° to SE. The beds show flexural toppling at NE-facing and W-facing slopes, totally cover an area of 0.25 km². Flexural toppling has led to the formation of ridge-top depression and bulging slope at the middle slope. Active unit of the slope deformation appears at the lower slope of W-facing slopes indicated by a slope failure and its debris deposit that looked quite fresh, suggesting they probably formed recently.