2018 Volume 70 Issue 6 Pages 54-57
A landslide occurred in the left-hand stream of the Umi River in Itoigawa, Niigata on October 23, 2017, blocking the main channel of the Umi River. We studied the landslide in order to determine the processes involved, from occurrence to deposition of the landslide. The results showed that the mass of soil that formed the landslide travelled about 400 m from the source area, with the shape of the soil mass remaining almost unchanged, and blocked the main channel of the Umi River. In addition, the landslide blocked the exit of the left-hand stream of the Umi River and muddy sediment was deposited behind the main soil mass of the landslide. Moreover, the sediment deposited behind the mass became muddier because of the continuing supply of stream water.
