1985 Volume 37 Issue 5 Pages 14-23
Topographical change in the Kamikamihori valley on the Yakedake volcano was quantitatively explained in terms of the processes of debris production, transportation and deposition. Rack fall from the flat sidewall was most active in early spring when the air temperature rises rapidly crossing 0°C, while from the convergent sidewall, rock fall was most active under the condition of water convergence by rapid snow melting or by heavy rainfall. But the rock-fall rate was not directly promoted through the wall-foot scouring by debris-flow passing. The retreat rate of sidewall took the large value amounting to the order of 101cm/year. Depositional structure of debris-flow lobe assumed the inverse grading, and the swollen lobes in the upper fan consisted of the sandy boulder deposits conserving the original composition of moving material in the flow, while the flat lobe in the lower fan consisted of the boulderly sand deposits almost losing the larger boulders. Topographical analysis of transversal cross profiles of the fan along the survey lines of concentric circles around the fan apex, was very useful for the prediction of the shifting of running direction and depositional pattern of debris flows, in addition to the explanation of the fan evolution itself.