On September 14, 1984, the Otaki earthquake (magnitude 6.8) in Nagano Prefecture, Japan, caused a major mudslide on the south face of Mount Ontake, which reached speeds of 80~100 km/h. Heavy rain over several days prior to the quake contributed to causing the mudslide, known as Ontake Kuzure, which took the lives of 29 people. After the disaster, barriers against mudslide were erected in nine locations at the foot of Mt. Ontake.