Study on Environmental Pollution Mechanism of Mt.Sakurajima Volcano Ash

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Mt.Sakurajima volcano is the most active one in Japan.and has been erupting large amount of volcanic ash around the mountain.The deposited volcanic ash on the mounainside results in debris flow in the rivers caused by heavy rainfall.Assuming that a particle erupted from the crater into the air falls at its terminal velocity,a theoretical equation which gives the depositing rate of volcanic ash and the distribution of grain size on the ground was obtained.A parametric model to predict the hydrograph of debris flow was offered,in which the distribution of slope length and the depth of the deposited volcanic ash were introduced.The parameters of the model are the mean and standard deviation of the depth of deposits,the hydraulic conductivity,and the lag time in the stream,which are identified by use of the Simplex method.The applicability of this model was checked by the data from two rivers in Sakurajima Volcano.