Research on eruption phenomena of dacite magma

点击翻译按钮获取中文摘要

Unzen Volcano started its eruption in November 1990, and dacite lava has erupted continuously sice May 1991. The head reseacher keeps monitoring of this activity. The eruption style of lava dome at Unzen is unique, and was not recorded at any other volcanoes in the world during historic time. In order to understand the magma supplying system under Unzen Volcano, petrological work was carried out.Lava remained constant in chemistry and mineral composition during three years, and microphenocrysts of lava were always same in dimension. The mineralogical texture showed several lines of evidence for magma mixing just before eruption for iace lava. The following mechanism was proposed for these facts ; 1) chamber was filled with dacite magma which resulted from mixing of andesite and dacite, 2) degassing of magma during ascent caused crystallization of microphenocrysts and microlites, resulting in the formation of texture showing reaction relation. However, the cause of eruption-rate change can not be explained only by this mechanism. The mechanism which explains the change in eruption rate should be establish by further investigations.