Analysis of Heavy Rainfalls Which Cause Debris Flows at Mt.Unzen and Construction of Advaced System for Disaster Prevention

长崎县云仙火山的喷发对岛原和前江地区造成了非常可怕的破坏。暴雨泥石流灾害一直是人们关注的焦点。本研究项目的主要成果如下。(1)暴雨过程中，在长崎半岛西南部附近出现了小规模的暴雨单体，在登陆岛原半岛（Mt. Unzen）。这些发育细胞的运动过程和速度显示出一些共同点。这一事实表明，有希望的强降雨和泥石流的即时预报。(2)针对泥石流灾害风险控制系统中存在的紧急信息传递和居民安全转移问题，对泥石流灾害风险控制系统进行了广泛的研究。迄今为止，人们在泥石流中的安全幸运地受到了火山碎屑流的限制。然而，最近由于火山碎屑活动减少，禁止进入的土地面积减少;因此，应立即提供气象条件和警报的信息，以便建议此后的疏散。(3)火山碎屑流和泥石流遗迹的地质调查明确表明，即使在云仙火山的北方斜坡，火山活动所产生的碎屑流和泥石流也是频繁发生的，其间隔时间为几千年至上万年。

The eruption of Unzen Volcano in Nagasaki Prefecture has caused very terrible damages at Shimabara and Fukae region. Our attention have been concentrated on the disasters derived from heavy rainfall and debris flow. The main results of this research project are as follows.(1) The behavior of heavy rainfall systems which caused violent debris flows showed that small-sizedconvetive rain cell appeared near the southwestern region of Nagasaki Peninsula move to ENE growing very rapidly before landing on Shimabara Peninsula (region of Mt. Unzen). These traveling course and velocity of developing cells showed something in common. This fact indicates the promising immediate prediction of strong rainfall and debris flow.(2) An extensive investigation on the risk control system agaist the debris flow disastars has been made in view of the problems on the transfer of urgent information and the induction of habitant to places of safety. The safety of people from debris flows have been fortunately kept up by the restriction of admittance for avoiding pyroclastic flows so far. However, the land area of no admittance is recently reduced because of decrease in pyroclastic activity ; so that the information on the meteorological coditions and warnings should be offered immediately in order to recommand the evacuation hereafter.(3) It has been definitely shown by the geological investigation on the traces of pyroclastic and debris flows that even at the northern slope of Unzen Volcano, those flows originated with the volcanic activities had taken place so frequently as an interval of several to ten thousand years.