Tadanori ISHIZUKA, Akihito KAJI, Takahisa MIZUYAMA, Kosuke YOSHINO, Yosuke NISHIO, Koji MORITA and Takao YAMAKOSHI
Outburst floods caused by landslide dams have brought devastating damage to various parts of the world. In July 2012, a landslide dam subsequent to the large]scale collapse of a mountain edifice occurred on Ambon Island in the eastern part of Indonesia. A height of the dam was approximately 140m and a volume of dammed water was approximately 25million m3. The dam failed about a year after its formation in July 2013, and a large]scale flood swept away two third of houses and buildings in a downstream village with a population of more than five thousand. Authors have conducted field reconnaissance survey several times before and after the outbreak of the landslide dam and installed interval recording cameras. We fortunately recorded images of the process of the outburst flood by one of the installed cameras, and video images which had been taken by the Ministry of Public Works of Indonesia and villagers were obtained. In this study, we derived events leading the progress of the outburst flood from obtained images and clarified the process of landslide dam outburst flood through the analysis of chronology of those events. Some of characteristic events, such as abrupt expansion of the width of water channel formed on the slope of the landslide dam and large]scale collapse of side bank of water channel was observed by the monitored images. The process of destruction of partially]built structures on the landslide dam, changes of longitudinal profile through the outburst flood and some other processes of the flood are discussed, and results of this paper and previous studies based on numerical models and channel experiments are compared.
Key wordsFlandslide dam, outburst flood, overflow and erosion, monitored images, chronology of events