Secondary Processes Associated with Landslides in Vietnam

Landslides are one of the most dangerous geohazards in tropical monsoon countries. Various impacts of landslides on lives and property not only result from the destruction of the down movement itself but is also due to secondary effects including the formation of landslide-dammed lakes and the generation of tsunami-like waves. This paper presents a study on secondary processes associated with landslides hazards in Vietnam through site surveys, air photos, and data collection and analysis. First, the paper reports a comprehensive investigation of the study on landslides and their consequential hazards in recent 30 year. Then, three typical cases of landslides in the Van Hoi reservoir, Khanh waterfall, and Song Bung hydropower reservoir are characterized in terms of geological features, causes, and sliding mechanisms. Besides, landslide hazard assessment for disaster risk reduction is briefly discussed. Study results significantly indicate that heavy rainfall is the main trigger for landslides and its cascading effects (i.e., river damming and dam breach, and landslide-generated waves). While the geological structures of high fractured, deformed, and weathered rocks are the main preparatory factor of the landslides. Landslides associated with secondary hazards has been rarely analyzed in Vietnam, this study will, therefore, bring a significant understanding for planning and management of multiple disaster risk in the river-hillslope system.