Landslides and Multi-Hazards

Landslides occur frequently in connection with other types of hazardous phenomena such as earthquakes and volcanic activities. Strong earthquakes often cause a large number of landslides, including large-scale landslides, in mountainous areas. Volcanic activities could trigger giant landslides or debris avalanches on mountain slopes. It is not uncommon that such large-scale landslides cause river blockage and form natural dams, which are vulnerable to collapse by overtopping and breaching. The sudden collapse of a landslide dam can cause a catastrophic flood in the downstream area. Submarine landslides are also common phenomena. Large-scale submarine landslides cause catastrophic tsunamis. In assessing those catastrophic cases as a whole, it is necessary to pay special attention to extremely high threats to vulnerable settlements in hazardous areas. The risk assessment of such complicated combined landslide disasters around the world, particularly in developing countries, is a significant step for identifying the appropriate mitigation strategy against catastrophic damage. In recent decades we have experienced remarkable disasters induced by landslides. For example, a huge number of landslides were induced by the Chi-Chi earthquake in Taiwan (1999), by the Mid-Niigata Prefecture earthquake in Japan (2004) and the Northern Pakistan earthquake (2005). Most recently the Wenchuan earthquake occurred with magnitude 8.0 in central part of China on May 12, 2008. This gigantic earthquake caused a tremendous number of landslides, as seen in the satellite picture in Fig. 23.1. Large-scale landslides occurred in volcanic areas, such as at Stromboli Volcano in Italy (2002) (Fig. 23.2) and on Leyte Island in Philippines (2006) (Fig. 23.3). Whole such events manifest the significance of a thematic session within the First World Landslide Forum focussing on the issue of risk mitigation targeting “landslides and multi-hazards”.