Eruption mechanisms and mineral textures of the ejecta

(1)富士火山喷出物的岩石学比较研究：我们研究了3000yBP的Omuroyama侧翼喷发、公元864年的Jayan喷发和AD的岩石学特征。1707年，为了了解富士火山喷出物的晶体结构与喷发方式之间的关系，他进行了一次喷发。斜长石、斑晶和微斑晶的成分分带揭示了岩浆上升和喷发过程中含水成矿岩浆的脱气和补给过程。玉山火山喷发3000年，沉积有少量斜长石微斑晶的下伏火山碎屑沉积，表明喷发前水的排出作用使岩浆结晶时间有限。公元864年喷发产生20-30%的斜长石斑晶，通常在边缘附近具有反向分带，表明岩浆在喷流喷发之前被含水的玄武岩浆对脱气的浅层岩浆进行了补充。(2)MAG…效应的模拟实验有关岩浆混合的更多信息：本实验旨在研究两种岩浆在低雷诺数下的混合过程。以往的实验(如Blake和Campbell，1986)只考察了高雷诺数下的混合条件。岩浆袋的存在增加了层流环流的不稳定性，这是因为重力对粘性力的作用增加了。结果表明，当无量纲参数i(=粘性力/重力)小于0.1时，流动不稳定。对端员岩浆条件的分析表明，在温泉火山下的岩浆洞穴中存在流动不稳定。(3)火山喷发的水含量和水化作用：我们研究了公元1783年的安山岩-流纹岩玻璃。1108和13ka BP的Mama火山喷发产物。AD.1783和AD.1108喷出物的含水率为03-0.7wt%，而13ka喷出物的含水率为15-4wt%。在13ka火山玻璃的背散射电子图像中，我们在气泡泡壁玻璃的中心观察到了明显的水化前沿，表明旧矿床的高含水率是受玻璃的二次水化作用的影响。(4)次液线岩浆的粘度测定：a Kilauea拉斑玄武岩：晶相主要为辉石和斜长石，并有少量橄榄石。含晶体岩浆的相对粘度可用爱因斯坦-罗斯科-马什方程很好地解释，表明各向异性晶体形态的影响被晶体尺寸弥散的影响所抵消。B：MORB拉斑玄武岩：粘度测量使用的是ODP206MORB样品。晶相还包括辉石和斜长石，镜面含量的橄榄石。含晶体岩浆的相对粘度比爱因斯坦-罗斯科-马什方程的值大3-5倍，这可能是由于MORB电荷中斜长石的长径比较大所致。较少

(1) Comparative petrological study of volcanic ejecta of Fuji volcano: We examined petrographic features of the 3000ybp Omuroyama flank eruption, AD.864 Jyogan eruption, and AD. 1707 Hoei eruption to understand the relations between the mode of eruptions and crystal textures of the ejecta at Fuji volcano. Compositional zoning of plagioclase phenocryst and microphenocryst tells us the processes of degassing and recharge of hydrous aphyric magmas during the magma uprise and eruptions. The 3000 yr by Omuroyama eruption had subplinian pyroclastic fall deposit which contains limited amount of plagioclase microphenocryst, suggesting only limited time for crystallization of magmas due to degassing of water just before the eruption. The AD.864 eruption products 20-30% of plagioclase phenocryst often with reverse zoning near the rim, indicating magma replenishment of degassed shallow magma by hydrous aphyric magmas just before the effusive eruptions.(2) Analogue experiments of the effect of mag … More ma pocket on the mixing of magmas: This experiment intends to examine the mixing processes of two magmas at low Reynolds number. Previous experiments (e g. Blake and Campbell, 1986) only examined the mixing conditions at high Reynolds number. Presence of a magma pocket increases the instability of laminar annular flow because of the increase of gravitational force against viscous force. It is shown that flow instability occurs when the dimensionless parameter I (=viscous force/gravitational force) is less than 0.1. Analyses of the condition of end member magmas indicate that flow instability occurs in a magma pocket beneath Unzen volcano.(3) Water content and hydration of volcanic ejecta: We examined andesitic-rhyolitic glasses of the AD.1783, AD. 1108, and 13ka bp eruption products of Mama volcano. Water contents are 03-0.7 wt % for AD.1783 and AD.1108 ejecta, whereas they are 15-4 wt% for 13ka ejecta. In back-scattered electron images of 13ka volcanic glasses, we observed clear hydration front in the core of the vesiculated bubble wall glass, suggesting that high water content of the old deposits are affected by secondary hydration of the glass.(4) Viscosity measurement of subliquidus magmas:A Kilauea thoeiite: Crystal phases are mainly augite and plagioclase with minor amount of olivine. The relative viscosity of the crystal-bearing magma is almost well explained by the Einstein-Roscoe-Marsh equation indicating that the effect of anisotropic crystal morphology is counterbalanced by the effect of crystal size dispersion.B: MORB tholeiite: An ODP Leg 206 MORB sample is used for the viscosity measurement. Crystal phases also consist of augite and plagioclase with mirror amount of olivine. The relative viscosity of the crystal-bearing magma is larger than the values of Einstein-Roscoe-Marsh equation by a factor of 3-5, which may be due to the higher aspect ratio of the plagioclase in the MORB charge. Less