Chih-Yu Kuo Chih-Yu Kuo Division of Mechanics,Research Center for Applied Sciences,Academia Sinica, Taiwan Rou-Fei Chen Institute of Earth Sciences, Academia Sinica Kuo-Jen Chang, Hou-Yen Li, Wei-Cheng Hung, Yih-Chin Tai NTUT, AS, NCNU

Chi-Chi epicenter Landslides ~ 350 x 10 6 ton 5 mm erosion

Morphologic mapGeologic map Physiographical and geological presentation

Tsaoling Before Chi-Chi earthquake After Chi-Chi earthquake Large landslide and torrential erosion of mountain belt : the case of Tsaoling triggered by the Chi-Chi earthquake

Historic landslide events in Tsaoling area Time Trigger Landslide process Slide volume (Km 3 ) Dam height (m) Effects 1862Earthquake (M L =6-7)Landslide formation of a dam 1898Rainfall (?)Landslide dam broke 1941Earthquake (M L =7.1) persons killed and formation of a dam 1942Rainfall (776cm) persons killed and increased landslide dam 1951Rainfall (770cm) persons killed and broke landslide dam 1979 Rainfall (327cm) Landslide formation of a dam Rainfall (624cm)0.040Landslide dam broke 1999Earthquake (M L =7.3) persons killed and formation of a dam 1941

Geological map of Tsaoling region after Chi-Chi earthquake, with 1m LiDAR images Large earthquake-triggered landslides and mountain belt erosion: the Tsaoling case, Taiwan Publishing in 2005, C. R.Géosciences 337, 1164–1172.

Co-seismic stage of 1999 Chichi earthquake Overview Tsaoling area with 1998 DEM and 1999 DEM Before 1999, 1998_5m DEMAfter 1999, 1999_5m DEM

Volumetric analysis of landslides: the case after the reactivation by Chi-chi V ac > V ar car 20% decompaction Co-seismic stage of 1999 Landslide area V 1 The cut volume : X 10 6 m 3 The fill volume : 1.2 X 10 6 m 3 Chihshui valley V 2 The cut volume : 14.8 X 10 6 m 3 The fill volume : 138 X 10 6 m 3 V2V2 V1V1

Continuum shallow water equations over general topography Basal topography: Basal normal vector: Velocity, pressure: Conti & momentum eqs: Boundary conditions: – Basal surface: With Coulomb friction – Free surface Small curvature Uniform velocity profile Shallowness

Godunov/MUSCL shock capturing Suliciu Approximate Riemann solver with vacuum handling Well-balanced for the resting condition 5m x 5m grid size, 1016 x 866 grids Best fit friction angle by minimizing standard deviation Tsaoling landslide simulation The governing equations, under Eulerian fluid with basal Coulomb friction: Simulation of Tsaoling Landslide, Taiwan, Based on Saint Venant Equations over General Topography Publishing in 2009, Eng. Geology Best fit Coulomb friction angle Volume dilation factor 1.36

Anisotropic constituent, e.g. Mohr-Coulomb material Binham/H-B fluid Eulerian w/ Coulomb friction Invscid Is basal friction-only model good enough? Hierarchy (complexity) of continuum shallow-water type Comparison to the apparent Friction angle from DEM simulation (Campbell, 1995) Tsaoling landslide Jiufenershan landslide

CHY080 Strong motion recordsWaterfall sequence on the main profile

-Fast Vegetation of the landslide; -Many alteration work of the landslide (drains at the top of the landslide region); -Reactivation and movements upstream of the landslide area Cover of air-photograph in 1999 and 2004 Topographical changes revealed by high-resolution airborne LiDAR images: The 1999 Tsaoling landslide induced by chichi earthquake, Taiwan Publishing in 2006, Eng. Geology, 88,

Time cut volumes (V 1 )fill volumes (V 2 )erosion volumes after 1999 event (V e )Corrected altitude km km km m km km km m km km km m Erosion volumetric analysis of post-landslide: the case after the reactivation by Typhoon Toraji 2001

Landslide area Deposit area Erosion volumetric analysis of post-landslide: the case after the reactivation by Typhoon Toraji 2001 Monitoring surface changes induced by landslide events base on sediment transport and DEM Analysis Sumitting in 2009, Geomorphology.

1 2 3 Volumetric analysis of landslide: the case after the reactivation by Typhoon Toraji 2001 (99’~03’)

1 2 Volumetric analysis of landslide: 2003~2007

m

240m

The calculated scar volume was about km 3 ; the deposit volume was about km 3, which suggests a volume increase of 19% during the landslide event, as a consequence of the decompaction during the landsliding. The high-resolution digital elevation model derived form the recent airbone LiDAR data enabled us to map and analyse in more detail. The LiDAR data allowed comprehensive investigation on spatial patterns and morphological features occurring along the sliding surface and fill areas. The calculated eroded volumes (about 0.01 km 3 /yr in the deposit area of the landslide, for a period of nearly 4 years) are very large with respect to the size of the affected area, giving very high local denudation rates. It would be quite logical to reconstruct rapid erosion just after dam emplacement and decreasing erosion later. A major typhoon (Toraji, July 2001) hit the are during the second period. Large values highlight the importance of landslide process of long-term denudation in the Taiwan. Conclusion and discussion