Smith Lecture: Volatiles in Magmas - Learning from Laboratory Studies About Volcanic Eruption
Active volcanoes are part of our daily life. Seldom have more than a few weeks passed without news of a dramatic eruption somewhere on Earth, and highly populated areas like Naples on the foot of Vesuvius live permanently with the threat of an upcoming new catastrophe. Eruptions may not only affect the direct environment of a volcano, but ashes and gases ejected to the stratosphere may have large impact on climate as well. Hence, there is large interest to improve forecast of eruptions. Pre-requisite is an understanding of the fundamental processes in magmas, including the knowledge of chemical and physical properties of volatile-bearing magmas.
The style and evolution of volcanic eruptions are strongly controlled by volatile release during magma ascent. Major volatiles in magmas are commonly water, carbon dioxide and sulfur, but halogens may also be important. The behavior of the volatiles during degassing is strongly affected by their solubility and mobility in silicate melts. These are key properties determining at which pressure (or depth) magmas become volatile-oversaturated and how fast bubbles can nucleate and grow. Both properties are closely related to the way how volatiles are incorporated in the melt structure. Laboratory studies can give quantitative constraints of these properties, but are useful to simulate the evolution of volatiles during magma decompression as well.
In this presentation an overview is given on solubility, diffusivity and structural incorporation of water, carbon dioxide and sulfur species in silicate melts. Laboratory strategies and methods are shown to get such information. Implications for magma degassing are discussed.