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

气体驱动的火山喷发是一种主要的自然灾害。这些喷发是由H2O和其他挥发物从岩浆中的出溶提供动力的。这个过程很复杂，要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（一种含硅77%的岩浆）的大部分基本数据已经通过实验确定。然而，有一个关键的需要进行实验研究的英安岩岩浆，含有约65重量%的二氧化硅和常见的爆炸性喷发，如1980年爆发的圣海伦火山，1991年爆发的皮纳图博火山，和1991年喷发的云仙山。根据这项授权，水在英安质熔体和玻璃中的扩散将在很宽的温度，压力和H2O含量范围内使用脱水和扩散偶实验进行研究。实验将在一个大气压炉，快速淬火冷密封压力容器，内部加热的压力容器，和活塞缸装置。将通过傅里叶变换红外光谱法分析含水物质浓度，并使用非线性扩散方程对扩散曲线进行建模。研究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.