Method for Real-Time Evaluation of Discharge Rate of Volcanic Ash – Case Study on Intermittent Eruptions at the Sakurajima Volcano, Japan –

A method for evaluating the volcanic ash discharge rate by using seismic and ground deformation signals is proposed to obtain this rate in real time for southern Kyushu’s Sakurajima volcano. This volcano repeats vulcanian eruptions accompanying significant ground deformation showing deflation and nonvulcanian type eruptions that emit the minor emissions of volcanic ash associated with volcanic tremors but without significant ground deformation. We examined ground deformation and seismic amplitude as they relate to monthly sums of volcanic ash weight ejected from craters. We found that in monthly sums, both deflation ground deformation and the amplitude of volcanic tremors correlate positively with the weight of ejected volcanic ash. A linear combination of terms for ground deformation, seismic amplitude and a correction factor correlates better than single parameter of deflation or seismic amplitude with volcanic ash weight. The linear combination provides the volcanic ash discharge rate in quasi-real time and the total amount of volcanic ash distributed over a wide area immediately after a volcanic eruption ends.