Ōsawa Failure

Ōsawa Failure is an erosional valley carved into Mount Fuji's western slope, forming a deep gorge through the mountain's volcanic terrain. The formation displays alternating layers of ancient lava flows and lightweight stone that shape its distinctive structure.

The valley began forming approximately one thousand years ago through repeated volcanic activity and the interaction of erosion with layered lava deposits. Over centuries, water pathways carved deeper into this volcanic material, expanding the gorge.

The Mount Fuji Sabo Office, established in 1969, represents Japan's commitment to managing natural disasters through engineering and environmental protection methods.

The valley is most active during rainy periods, when heavy water flow moves through the gorge and carries loose material downslope. Visitors should check conditions before exploring the surrounding area to ensure safe passage.

Engineers have built sediment-control barriers using heavy concrete blocks throughout the gorge to slow debris flows and protect downstream communities. These structures reveal how human engineering works alongside natural processes to manage hazards.