Landslide dams induce catastrophic outburst floods or debris flows mostly by overtopping. However, adequate information about sediment transport of landslide dam and changes of grain size distribution due to overtopping are still lucking. The2008Iwate and Miyagi inland earthquake triggered15landslide dams. Here we showed new data about the sediment transport of two landslide dams occurred by The2008Iwate and Miyagi inland earthquake due to overtopping erosion by the LiDAR data. We measured at3times, before overtopping erosion (just after the earthquake), after the overtopping erosion, around4mouths after the overtopping erosion).We found that about only1/2`2/3was eroded by the overtopping among the height of a landslide dam, and the water channel is formed in overtopping erosion; it had indicated that the water channel is wide in the downstream more than upstream. One side a part of the sediment from a landslide dam has deposited between landslide dam and small]scale landslide dam in the downstream, and the longitudinal riverbed gradient approaches to initial gradient. In addition, after overtopping erosion once, the substantial change was not seen in the shape of a landslide dam though there was a rainfall of the total about120mm.

Key wordsFIwate and Miyagi inland earthquake, landslide dam, overtopping erosion, sediment transport