焼岳上々堀沢の谷壁と渓床における地形変化過程

Abstract

Progress of rock fall from the sidewall was observed, and the surveys for the topographyof valley bottom were repeated, at the Kamikamihori valley on the eastern slope of theYakedake Volcano, in Japan Alps. The progress of rock fall from flat sidewall was mostactive in early spring when the air temperature rises crossing 0°C, while, from convergentsidewall, progress of rock fall was most active under the conditions of rapid snow melting orof heavy rainfall. The retreat rate of sidewall estimated from those rock-fall data amountedto the order of 10 1 cm in one year. The continuous talus belt was laterally formed along thefoot of flat sidewall, while a larger and solitary talus cone was composed on the foot of eachconvergent sidewall. The latter types of talus cones yield stepwise shape on the longitudinalprofile of valley talweg. This stepwise topography in talweg would diminish or retreat inparallel due to the running down of debris flow. The lateral inclination of flow surface ofdebris flow at the curved section of valley bottom, was observed to be several times as muchas that by water stream under the same hydrological conditions.