| Budget Amount *help |
¥1,100,000 (Direct Cost: ¥1,100,000)
Fiscal Year 1988: ¥300,000 (Direct Cost: ¥300,000)
Fiscal Year 1987: ¥800,000 (Direct Cost: ¥800,000)
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| Research Abstract |
In order to summarize the characteristic features of tephra ejected during the evolution of a volcanic edifice, representative volcanoes in Japan were studied and many modes of eruptions were recognized. However mainly tephra ejected by vulcanian and plinian eruptions are considered in this study.
Isopach maps of tephra of vulcanian eruptions are nearly circular or somewhat elongated to the southeast owing to the intermittent eruptions over a long period and to the annual frequencies of wind direction above the volcanoes. On the other hand, those of plinian activity are not necessarily circular, probably due to the short period of volcanic activity.
The rate of evolution of a volcanic edifice in the vulcanian eruptions is closely related not only to the volume of the ejected magma but also to the height of the crater from the base of the volcano, whereas in plinian activity, it is also governed by the violence of eruption.
The morphology of volcanic ash varies greatly ranging from vesiculated to polygonal. A small amount of glass fiber, which is rare in Japan, was found in the volcanic sand deposit from Kuchinoreabujima Volcano.
No common feature was observed in the chemistry of tephra and lava from the volcanoes studied.
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