火山喷发形式与挥发分含量

Style of volcanic eruption and volatile content

火山喷发是由地球深部物质发生部分熔融产生的岩浆上涌至地表所形成的一种地质现象,是地球内部能量释放的主要途径之一。有些火山喷发极为猛烈,产生的大量火山灰能够在长达几个月的时间内影响当地气候环境,甚至可以在一瞬间掩埋整座城市;而有些火山喷发时只有大量的熔岩从火山口中静静地溢出,人们甚至可以在不远处进行观赏。火山喷发具有何种程度的破坏力取决于其喷发形式,而挥发分含量是影响喷发形式的重要因素之一。本文简述了几种常见的喷发形式及其相互之间可能存在的转化关系,着重论述了挥发分含量在其中所起到的作用,同时介绍了几种可能的去气模型及常见的测量岩浆挥发分含量的方法。其中使用单斜辉石斑晶来反演大陆玄武岩原始岩浆水含量的方法预计会在未来的研究中得到普及。

Magma formed by partial melting of the deep-earth materials, upwelling to the surface, causes a volcanic eruption, which is one of the major ways for the earth to release its energy. Explosive eruptions can affect the local climate and environment for several months by its tephra covering the entire atmosphere, even burying a city at one moment; on the contrary, effusive eruptions may only contain lava outtlowing from its vent, during which people can observe it not far away. The energy released during one eruption depends on its eruption style, which is controlled largely by the volatile content. Volcanic eruptions may contain various eruption styles. This paper introduces the most common ones and discusses the possibility how they can transform to each other, revealing that the volatile content has played an important role on controlling the eruption styles and then offer some ways of degassing. In addition, several commonly applied methods to calculate the volatile content have been described. Among them the method which uses the clinopyroxene phenocryst to calculate the water content of the primitive magma may get generally accepted in the future.