The Central Asia region has been a scene of numerous large-scale bedrock landslides that have blocked river valleys producing landslide-dammed lakes, more than 100 of which still store water. The largest one is the Usoi dam 2.2 km3 in volume and more than 550 m high in Pamirs (Tajikistan) that originated in 1911 due to strong (M7.2) earthquake. It forms the 500 m deep Sarez Lake - the world deepest natural reservoir that poses a threat to Central Asian countries located downstream in the Pianj - Amu Daria River basin. Though many of landslide-dammed lakes should be considered as stable and safe features, catastrophic outburst floods that occurred in 20th Century, emphasize high potential hazard of such natural blockages. Several prehistoric landslide-dammed lakes in Pamirs and Tien Shan with intact dams were filled by lacustrine sediments, but most of natural dams were breached and deeply eroded providing excellent opportunity to study their internal structure and grain-size composition - parameters determining dams' short-term and long-term stability at a large extent. Additional factors, increasing or decreasing rockslide dams stability are exemplified by case studies from the Central Asia region.
Recently, large-sized landslides causing a river blockage due to high magnitude earthquake occur and form a number of landslide dams. The water blocked by the dam may provoke floods which spread out the down stream area, causing damages to human activities and communication lines. The establishment of prediction method of landslide dam formation is expected to prevent these disasters. To clarify the moving mass phenomena of landslide due to earthquake, the equation having high advection velocity is necessary to analyze. This paper discusses a numerical method preventing for numerical oscillation due to the discretization of convection term by using stabilized finite element method combined with slope limiter function method and shock-capturing method of second-order accuracy. The presented analysis method poses the preventive function of numerical oscillation, the accuracy and utility of analysis scheme are confirmed in comparison with model analysis and actual landslide dam phenomena
A landslide of 1000m in width and relative height and 1500m in slope length occurred on the right bank of the Hunza River, northern Pakistan in Jan., 2010. Detritus with a volume of ca 40 million cubic meters dammed up the Hunza River. They mainly consist of boulders in a maximum scale of 10m long with fine sand to silt as matrix. Such fine materials were squeezed up and flew on the mound as mudflow. The mudflow killed 19 peoples in the down stream. They were the only victims due to the landslide disaster. Possibility of sudden burst of the landslide dam is presumably low because of large size component. 3D interpretation of space images of ALOS/PRISM clarified development of scarplets deforming valley slope as pre-cautious signs of a landslide on a gigantic scale. Consequently, such technique should be applied to preparation of avoid mapping for gigantic landslides causing natural damming in the high relief region as Himalayas.