| 英文摘要: | One of the large-impact natural hazards to affect humans on a decadal time scale are highly explosive Plinian volcanic eruptions, whose dynamics are thought to be intimately linked to the manner by which magmatic gases, such as water and carbon dioxide, escape from the erupting magma. Magma degassing begins with the nucleation of bubbles, which are preserved as vesicles in the erupted volcanic rock fragments. It is thought that the number and size of bubbles in a given volume of volcanic rock provide records of the forces that drive bubble nucleation and, by inference, the dynamics of the eruption. Specifically, the speed at which magma rises to the surface, thereby undergoing decompression, and the rate at which bubbles nucleate are thought to be correlated and affect the explosive intensity of an eruption. About one million bubbles may nucleate within a cubic millimeter of magma over fractions of a second to a few seconds. This transformation from dissolved gases to gaseous bubbles under high pressure is a key mechanism for explosive eruptions. Current models for the rate of bubble nucleation during explosive eruptions are based on Classical Nucleation Theory. A preliminary analysis of laboratory experiments of bubble nucleation in magmas, where conditions (pressure, rate of decompression, composition, content of dissolved gases, temperature) are well known and controlled, has shown that this classical theory fails to predict the rate at which bubbles nucleate across a wide range of conditions. A fundamental issue in this regard is the requirement for decompression rates that may be higher than physically attainable during an eruption, thus over-predicting rates of magma ascent.
The objective of this project is to obtain a new formulation for the rate bubble nucleation, which will be applicable across a wide range of conditions of relevance to explosive volcanic eruptions. This will be accomplished through an integrated study that is comprised of laboratory experiments of bubble nucleation in silicate melts and detailed numerical modeling of these experiments. The result of this study, that is a new formulation for bubble nucleation in silicate melts, will be incorporated into numerical models of explosive volcanic eruptions, thereby enhancing their predictive capabilities. These models, in turn, will be used to resolve the question of what the precise relationship between magma decompression rate and the number of bubbles that nucleate within a given volume of magma is, thereby allowing a more robust integration of observationally based studies with quantitative predictions through numerical modeling and hazard assessment. Moreover, nucleation theory is of importance in a wide range of disciplines, such as for example chemical engineering and material science. Because this project will integrate recent advances in other fields where Classical Nucleation Theory has been found inadequate, it will advance the state-of-the-art and also have the potential to impact other disciplines. |