Influence of Magma Properties on the Dynamics of Explosive Eruptions

对El Chichon（1982）和Vesuvius（公元79年）爆发喷发产物的物理火山学和实验岩石学研究已经阐明了喷发过程对岩浆性质的依赖性。公元79年维苏威火山喷发期间，两种截然不同的岩浆在喷发过程中混合在一起，导致喷发产物的成分梯度复杂。混合程度与整体喷发速率密切相关，这是基于成分分层储层的理论基础提出的，并表明火山矿床的地球化学梯度只能与喷发动力学信息相结合来解释。利用岩石学推断的密集参数对维苏威火山和埃尔奇川火山序列进行建模表明，喷发过程的演化与目前的喷发柱行为模型一致，两个中心事件之间的差异可归因于各自岩浆的挥发物含量、结晶度和粘度的差异。物理火山学的新技术现在提供了计算近代和古代爆炸性喷发强度（大规模喷发率）的方法。对现有的全球爆炸喷发强度和震级（喷发岩浆的总量）数据库的分析表明，它们之间存在密切的相关性，表明强度取决于震级，反过来又取决于储层的大小。强度超过2x10- 8kg /s的喷发总是与主要火山碎屑流的产生和火山口崩塌有关。火山碎屑流的跳动距离与前普林尼期的强度也存在相关性。这些观测结果的预测能力对火山灾害研究具有重要意义。本项目将继续开展物理火山学和实验岩石学方面的工作，并将以往的研究成果应用于美国喀斯喀特山脉古代爆炸性喷发的强度、震级和岩浆成分的调查。该研究将有助于了解该地区的喷发过程、岩浆演化和危害评估。

Collaborative studies in physical volcanology and experimental petrology on products of explosive eruptions of El Chichon (1982) and Vesuvius (79 AD) have elucidated the dependence of eruption processes on magma properties. Variation in mass eruption rate during the 79 A.D. Vesuvius eruption produced complex compositional gradients in the erupted products, as two contrasting magmas were mixed during withdrawal from the chamber. The extent of mixing is closely linked to mass eruption rate, as proposed on theoretical grounds for compositionally-stratified reservoirs, and demonstrates that geochemical gradients in volcanic deposits can only be interpreted in conjunction with information about eruption dynamics. Modelling of the Vesuvius and El Chichon sequences using petrologically-inferred intensive parameters has shown that the evolution of eruptive processes is consistent with current models of eruption column behavior and that differences between events at the two centers can be attributed to contrasting volatile contents, crystallinity and viscosity of their respective magmas. New techniques in physical volcanology have now provided the means to calculate the intensity (mass eruption rate) of recent and ancient explosive eruptions. Analysis of the available global data base on intensity and magnitude (total volume of erupted magma) of explosive eruptions reveals a close correlation, suggesting a dependence of intensity on magnitude and in turn, on reservoir size. Eruptions with intensities in excess of 2x10-8 kg/s are invariably associated with major pyroclastic flow generation and caldera collapse. A correlation also exists between the runout distance of pyroclastic flows and the intensity of the preceding plinian phase. The predictive power of these observations is of great significance to volcanic hazards studies. This project will continue work in physical volcanology and experimental petrology and apply the results of previous studies to an investigation of intensity, magnitude, and magmatic composition of ancient explosive eruptions from the Cascade Range of the U. S. The study should contribute to an understanding of eruptive processes, magma evolution and hazards assessment of this region.