抄録
It is well known that debris flow can be triggered by low rainfall after volcanic eruptions have altered the characteristics of mountain slopes. We suggest that the reason for this is explained by the reduction of infiltration rates after soil surfaces are covered with pyroclastic materials, volcanic ash, etc. Specific data, however, have not been comprehensively reported. This paper reports on the results of laboratory experiments carried out on infiltration rates of the soils sampled in the Mount Unzen area. The results of the experiments were as follows. The infiltration rate of pyroclastic deposit is 14 mm/hr and those of the soils unaffected by the influence of pyroclastic flows are 105mm/hr minimum.
