Abstract
Volcano areas account for one fourth of the area of Japan. In the volcano areas, many debris disasters occur due to earthquakes, heavy rains and volcanic eruptions.
The author explains six natural disasters in the volcano areas at the time of heavy rain which occurs often in recent years. The feature of slope failure at the heavy rain indicates mainly surface slope failure based on geographical and geological structure. For example, the volcanic ash layer is weak to erosion and collapse. The layer collapses easily at the heavy rain because the layer deposits in parallel with a slope.
Moreover, there is a cap rock type slope failure as a serious disaster in the volcano area.
Where surface slope failure occurs in the forest-rich volcano areas, driftwood increases in debris flow relatively. The numerousness of driftwood gives a lot of downstream site damage and the subject of disaster waste treatment.
Finally, the author discusses the land use and legal system to decrease natural disaster damage in the volcano areas.
