Water Diffusion in Dacitic Melt and Glass, and Explosive Volcanic Eruptions

气体驱动的火山喷发是一种重大的自然灾害。这些喷发的动力来自于岩浆中水和其他挥发物的析出。这个过程是复杂的，理解它需要对许多变量和过程进行量化和建模，特别是水的扩散。经过多年的工作，高硅流纹岩（一种含有77%二氧化硅的岩浆）的大部分基本数据已经通过实验确定。然而，目前迫切需要对英安岩岩浆进行实验研究，这种岩浆含有约65%的二氧化硅，是1980年圣海伦火山喷发、1991年皮纳图博火山喷发和1991年云岑火山喷发等爆炸性喷发的常见岩浆。在这项资助下，将使用脱水和扩散偶联实验，在广泛的温度、压力和H2O含量下，研究水在英灰岩熔体和玻璃中的扩散。实验将在一气氛炉、快淬冷封压力容器、内加热压力容器和活塞缸装置中进行。含水物质浓度将通过傅里叶变换红外光谱进行分析，并使用非线性扩散方程模拟扩散曲线。这些结果将用于模拟英安岩中的气泡生长和岩浆破碎。

ZhangEAR-0228752Gas-driven volcanic eruptions are a major natural hazard. These eruptions are powered by the exsolution of H2O and other volatiles from magma. The process is complex, and understanding it requires quantification and modeling of a number of variables and processes, especially the diffusion of water. After many years of work, most of the fundamental data for high-silica rhyolite--a magma with 77 wt% silica--has been experimentally determined. However, there is a critical need for experimental studies of dacitic magmas, containing around 65 wt% silica and common to explosive eruptions such as the 1980 eruption of Mount St. Helens, the 1991 eruption of Mount Pinatubo, and the 1991 eruption of Mount Unzen. Under this grant, water diffusion in dacitic melt and glass will be investigated using dehydration and diffusion couple experiments over a wide range of temperature, pressure, and H2O contents. Experiments will be performed in one-atmosphere furnaces, rapid-quench cold-seal pressure vessels, internally-heated pressure vessels, and a piston-cylinder apparatus. Hydrous species concentrations will be analyzed by Fourier Transform Infrared Spectroscopy, and diffusion profiles modeled using a nonlinear diffusion equation. The results will be used to model bubble growth and magma fragmentation in dacite.