RESEARCH ON PREDICTION OF DEBRIS FLOWS AND DEVELOPMENT OF THE DISASTER PREVENTION SYSTEM

点击翻译按钮获取中文摘要

Mt. Sakurajima is the most active volcano in Japan, it has been providing serious damages in these last ten years by ashfall and debris flows. The purposes of this study are to investigate a predicting method of debris flows caused by heavy ashfall and rainfall and to establish a fundamental theory to reduce these disasters in this area.1. A relation between depth of deposited ash and an intensity of MSS-image by LANDASAT-4 is obtained. Observed distributions of the grain size coincide with theoretically calculated ones. A new calculating method of an amount of erupted ash was deduced from data of the eruption height, the rate of deposited ash around the crater and frequency of a wind direction in an upper layer. Every time ash is erupted, the amount can be calculated at about forty thousand tons in these last ten years. And it has attained to seventy thousand tons, and an annual amount of erupted ash reached into thirty million tons in 1985.2. For an analysis of occurrence condition o … More f debris flow in the Hase River, if the cumulative rainfall exceeds 7 mm, occurrence of debris flow is possible and an excess of 13 mm would certainly cause an occurrence. This result was confirmed by experimental data of newly deposited ash in a laboratory. Meanwhile, a model of outflow of debris was also obtained by computational experiments, considering distributions of deposited ash and of slope length, and it can be generally applied to the disaster prevention in Mt. Sakurajima.3. Image data by a radar hyetometer at Kunimiyama, which belongs to the Ministry of Construction, is daily obtainable at public offices in Kagoshima Prefecture. In June 1986, a heavy rainfall attacked Kagoshima City, and a horizontal plane distribution of slope collapses coincided with the intensity of precipitation by the radar hyetometer. Furthermore, we checked for occurrence of debris flow in Mt. Sakurajima with the intensity of precipitation, the result for probability of occurrence is useful to forecast for debris flows. Less