The Classification of Damming Landslides and Landslide Dams Induced by the Wenchuan Earthquake

The devastating 2008 Wenchuan earthquake with a magnitude of Mw 7.9 was the largest seismic event in China in more than 50 years. It triggered numerous landslides over a broad area, some of which dammed rivers, posing severe threats to downstream settlements. The coseismic landslides are classified into rock/debris avalanches, debris flows, rock/debris slides and rock falls. A number of representative examples of each type and the corresponding landslide dam features were studied. According to dam composition material and sedimentological features, landslide dams were categorized into three types: dams mainly composed of large boulders and blocks; dams composed of unconsolidated fine debris; and dams with partly intact rock strata at the base topped by large boulders and blocks or soil with rock fragments, showing two-layered or three-layered depositional structure. This classification is linked to the typology of damming landslides and considered to be a preliminary indicator of dam stability. In addition, dam stability also largely depends on valley morphometry as well as landslide runout distance and mechanism.