Research on eruption phenomena of dacite magma

温岑火山于1990年11月开始喷发，英安岩熔岩自1991年5月以来连续喷发。首席搜索者一直在监控这一活动。云顶熔岩穹顶的喷发风格是独一无二的，在历史时期世界上任何其他火山都没有记录过。为了了解温泉火山下的岩浆供应系统，进行了岩石学研究。三年来，熔岩的化学成分和矿物成分保持不变，熔岩的微斑晶在尺寸上也是相同的。矿物学结构表明，就在IACE熔岩喷发之前，有几条岩浆混合的证据。对此提出了如下机制：1)安山岩和英安岩混合形成的英安岩岩浆充填洞室；2)岩浆在上升过程中的脱气作用导致微斑晶和微晶的结晶，形成具有反应关系的结构。然而，喷发率变化的原因不能仅用这种机制来解释。解释喷发率变化的机制应通过进一步的研究来确定。

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.