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

樱岛火山是日本最活跃的火山，在过去的十年里，它一直受到火山灰和泥石流的严重破坏。本研究的目的是探讨强烟灰和强降雨引起的泥石流的预测方法，为减少该地区的泥石流灾害建立基础理论。得到了沉积火山灰深度与LANDASAT-4卫星mss图像强度之间的关系。观察到的晶粒尺寸分布与理论计算的一致。根据火山喷发高度、火山口周围的火山灰沉积速率和上层风向的频率等数据，推导出一种新的喷发火山灰量的计算方法。在过去的十年里，每次火山灰喷发的数量可以计算为大约四万吨。目前已达到7万吨，1985年每年喷发的火山灰量达到3000万吨。对哈斯河泥石流的发生条件进行了分析，如果累计降雨量超过7 mm，就有可能发生泥石流，超过13 mm就一定会发生泥石流。这一结果被实验室新沉积灰的实验数据所证实。同时，通过计算实验得到了考虑沉降灰分布和坡长的岩屑流出模型，该模型可普遍应用于樱岛山的灾害防治。国山的雷达湿度计的图像数据属于建设部，每天都可以在鹿儿岛县的公共办公室获得。1986年6月鹿儿岛市发生强降雨，坡体崩塌的水平面分布与雷达雨量计测得的降水强度一致。此外，我们还利用降水强度对樱岛山泥石流的发生概率进行了检验，其结果对泥石流的发生概率预报有一定的帮助。少

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