1977 年有珠山噴火で生じた噴煙柱の解析

概要

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The 1977 eruption of Mt.Usu generated four high-altitude eruption columns whichproduce BIGⅠ,BIGⅡ,BIGⅢ and BIGⅣ tephra-fall deposits respectively. Expressing theinitial eruption velocity in terms of the solid mass eruption rate, the initial temperature, theinitial radius and the initial gas fraction from the conservation of solid particles, we apply asteady plume model to the four eruption columns. The initial velocity increases with initialgas mass fraction and initial temperature for the solid mass eruption rate estimated from thevolume of deposits, the apparent density of tephra and the eruption duration. For threeeruption columns depositing BIGⅠ,BIGⅡ and BIGⅢ, the initial temperature and initial gasmass fraction are estimated at 600K and >0.11. The eruption column depositing BIGⅣ isformed at 800K and >0.15. The estimated initial temperature are low and initial gas massfraction are high in comparison with general physical properties of dacitic magma. Theseinadequate values suggest that the growth of eruption columns take the influence ofpyroclasts fallout from the column and thermal disequilibrium between pyroclasts and gases.
北海道大学大学院理学研究院自然史科学部門（地球物理学）の論文
2007-03-15