Role of carbon dioxide in the dynamics of magma ascent in explosive eruptions
Role of carbon dioxide in the dynamics of magma ascent in explosive eruptions
复制标题
二氧化碳在爆炸性喷发中岩浆上升动力学中的作用
DOI：
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发表时间：
1999
期刊：
影响因子：
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通讯作者：
M. Polacci
中科院分区：
文献类型：
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作者：
P. Papale;M. Polacci
摘要 用数值模拟的方法研究了二氧化碳在喷发过程中岩浆上升动力学中的作用。该模型是稳定的、一维的、等温的；它计算气体以及液态岩浆和晶体的均匀混合物的分离流动。岩浆性质是根据岩浆成分和晶体含量计算的，并允许由于压力下降和气体逸出而沿管道变化。通过对CO2/(H2O+CO2)比值的参数研究，研究了双组分(水+二氧化碳)溶解气相的存在的影响，在总挥发分或恒定水分含量下，CO2/(H2O+CO2)比值允许从0到0.5变化。相对不溶的二氧化碳组分在火山导管内挥发饱和度和岩浆破碎程度的位置以及流动变量的分布中起着重要的作用。结果表明，随着二氧化碳比例的增加，质量流量、压力和出口混合气密度减小，出口气体体积分数和破碎深度增大。一个相关的结果是水和二氧化碳在喷发动力学中扮演的不同角色；水的增加产生质量流率的增加，二氧化碳的增加产生减少。即使是少量二氧化碳也会对喷发动力学产生重大影响，这意味着在预测喷发情景和预测火山灾害时，必须考虑到火山气体的多组分性质。
Abstract The role of carbon dioxide in the dynamics of magma ascent in explosive eruptions is investigated by means of numerical modeling. The model is steady, one-dimensional, and isothermal; it calculates the separated flow of gas and a homogeneous mixture of liquid magma and crystals. The magma properties are calculated on the basis of magma composition and crystal content and are allowed to change along the conduit due to pressure decrease and gas exsolution. The effect of the presence of a two-component (water + carbon dioxide) exsolving gas phase is investigated by performing a parametric study on the CO2/(H2O+CO2) ratio, which is allowed to vary from 0 to 0.5 at either constant total volatile or constant water content. The relatively insoluble carbon dioxide component plays an important role in the location of the volatile-saturation and magma-fragmentation levels and in the distribution of the flow variables in the volcanic conduit. In detail, the results show that an increase of the proportion of carbon dioxide produces a decrease of the mass flow rate, pressure, and exit mixture density, and an increase of the exit gas volume fraction and depth of the fragmentation level. A relevant result is the different role played by water and carbon dioxide in the eruption dynamics; an increasing amount of water produces an increase of the mass flow rate, and an increasing amount of carbon dioxide produces a decrease. Even small amounts of carbon dioxide have major consequences on the eruption dynamics, implying that the multicomponent nature of the volcanic gas must be taken into account in the prediction of the eruption scenario and the forecasting of volcanic hazard.