A synthetic study on the forecast of occurrence of large-scale sediment disasters and the counter plan on the suburbs of the Mt.Unzn.

本研究的目的是分析5 -山山火山的大规模崩塌，以及云禅-富根纳克火山喷发时的火山灰沉积和火山碎屑流的碎屑流。由于大规模崩塌被认为是热液和地下水异常变化的原因和地震的影响，我们分析和观察如下：通过形态分析、放射性测量和电测等方法，从地质剖面和断裂线上确定了大规模塌陷的危险区。利用延伸仪、应变计、倾角计和加速度计对马尤山进行了观测。我们还调查了坍塌迹象和孔隙水压力，包括室内调查。计算了临界最大加速度和孔隙水压力，并将结果用于危险崩塌区域的绘制。利用gps连续观测，研究了云仙山火山活动与云仙地堑带活动的关系。我们正在观测与地震和地下水质量异常变化有关的泉水温度、地下水位、地下水和地质电流，以调查大规模坍塌的迹象。对沟壑条件对火山灰和火山碎屑流沉积的影响进行了连续分析，揭示了沟壑与泥石流规模的关系。利用火山灰流变学模型，分析了泥流的增加和流能的变化，绘制了洪水灾害图。研究结果为预防火山次生灾害提供了重要数据。

The objective of this study is an analysis of the large-scale collapse at Mt.May-uyama and the debris flows from deposit of volcanic ash and pyroclastic flow on the erupting Mt.Unzen-Fugenndake. Since the large-scale collapses are consid-cred to be the causes of unusual variations of hydrothermal water and ground water and the influence of earthquakes, we analyzed and observed as follows ; hazard area of the large-scale collapses was zoned from the geological profile and fault lines estimated by morphological analysis, radioactivity survey and electric prosoecting. Observations have been made using extensometer, strain meter, inclinometerand accelerometer at Mt.Mayu-yama.We also surveyed the sign of collapse and the pore water pressure including indoor investigations. The results were used in mapping of hazard collapse areas with calculations of critical maximum acceleration and pore water pressure. Relation between volcanism of Mt.Unzen and activities of graben zone at Unzen were also investigated with continuous observations using G.P.S.. We are obser-ving spring water temperature, groudwater level, groudwater and geological electric current which were concerned with carthquakes and unusual variations of ground water quality in order to investigate the sign of large-scale collapse. Continous analysis of condition of gully on the deposit of volcanic ash and pyroclastic flow indicates the relation between gully and scale of the debris flows. The hazard map of flooding was made using analysis of increasing mudflow and energy of flow by rhecology models of volcanic ash.The results of this study provide important data for prevention of secondary disasters caused by volcanic activities.