Debris Flows and Landslides - River Dynamics and Integrated River Management - page 189

along one or several sliding beds under the action of gravity. In many publications these mass movements
are all called landslides.
Figure 4.1 shows the four types of mass movement in mountain areas with high bank slope: (a) Topple—
detachment of columns of rock along the Juma River near Beijing; (b) Rockfall—a huge stone fell from a
steep slope along the Juma River; (c) Avalanche—mass movement of broken rocks down the bank slope
of the Minjiang River triggered by the Wenchuan Earthquake in 2008; (d) Landslide—movement of
slope debris and rocks induced by the Wenchuan Earthquake along the Qingzhu River in Sichuan, China.
Avalanche and landslide are the most important mass movements and the general term of landslides means
these two mass movements in the literature and this topic.
(a) (b)
(c) (d)
Fig. 4.1 Different types of mass movements: (a) topple; (b) rockfall; (c) avalanche; (d) landslide (See color figure
at the end of this topic)
Earthquake is often the direct cause of landslides. There have been many examples of earthquake-
induced avalanches and landslides. The 1999 Chi-Chi earthquake in Taiwan, China, induced landslides in
the Tachia catchment. The subsequent rainfall events associated with the passage of typhoons have led to
a significant increase in the area affected by landslides. As a result, the sediment production rate was still
increasing four years after the earthquake event (Lin et al., 2005). The relation between the magnitude of
an earthquake and the intensity of landslides has been studied. It was found that the minimum earthquake
magnitude needed generate a landslide is M = 4.3 ± 0.4 on the moment magnitude scale (Malamud et al.,
2004).