Eruption mechanisms and mineral textures of the ejecta

(1)富士火山喷出物的比较岩石学研究：我们研究了3000 ybp Omuroyama侧翼喷发，AD 864 Jyogan喷发和AD。1707年Hoei喷发，以了解富士火山喷发模式和喷出物晶体结构之间的关系。斜长石斑晶和微斑晶的成分分带反映了岩浆上升和喷发过程中含水无定形岩浆的脱气和补给过程。Omuroyama喷发的3000年有subplinian火山碎屑落存款，其中包含有限数量的斜长石微斑晶，这表明只有有限的时间结晶的岩浆，由于水的脱气就在喷发前。AD.864喷发产物中有20-30%的斜长石斑晶在边缘附近经常出现反向分带，这表明在喷发之前，含水无定形岩浆对脱气的浅岩浆进行了补充。(2)磁流变效应的模拟实验 关于我们 Ma口袋对岩浆混合的影响：本实验旨在研究低雷诺数下两种岩浆的混合过程。以前的实验（例如，Blake和坎贝尔，1986年）只研究了高雷诺数下的混合条件。岩浆袋的存在增加了层流环状流的不稳定性，因为重力对粘性力的增加。结果表明，当无量纲参数I（=粘性力/重力）小于0.1时，流动不稳定性发生。对端元岩浆状态的分析表明，云仙火山下的岩浆囊存在流动不稳定性。(3)水含量和水化的火山喷出物：我们研究了安山流纹岩玻璃的公元1783年，公元。1108年和13 ka bp的Mama火山喷发产物。AD. 1783和AD. 1108喷出物的含水量为03- 0.7wt%，而13 ka喷出物的含水量为15- 4wt%。在13 ka的火山玻璃的背散射电子图像中，我们观察到清晰的水化前沿的核心的泡状气泡壁玻璃，这表明，高含水量的老存款的影响，二次水化的玻璃。(4)亚液相线岩浆的粘度测量：A基拉韦厄硅铝榴石：晶相主要为普通辉石和斜长石，含少量橄榄石。Einstein-Roscoe-Marsh方程几乎很好地解释了含晶体岩浆的相对粘度，表明各向异性晶体形态的影响被晶体尺寸分散的影响所抵消。B：MOR B拉斑玄武岩：ODP Leg 206 MOR B样品用于粘度测量。晶相也由普通辉石和斜长石组成，并含有少量的橄榄石。含晶岩浆的相对粘度比Einstein-Roscoe-Marsh方程的值大3-5倍，这可能是由于MORB装药中斜长石的长径比较大所致。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