Crystallization and Degassing Processes during Strombolian Eruptions: A Numerical Approach

斯特龙博利火山喷发期间的结晶和脱气过程：数值方法

• 批准号: 419319298
• 负责人: Professor Dr. Matthias Hort
• 金额: --
• 依托单位: Department of the Geophysical Sciences
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2019
• 资助国家: 德国
• 起止时间: 2018-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/419319298?language=en
• 关键词: Crystallization; Degassing; Processes; during; Strombolian

Mankind’s interest in volcanic eruptions is probably as old as its existence because, on the one hand, volcanoes provide extremely fertile soil for farming leading to preferred settling grounds at or near volcanoes. Furthermore, they are probably one of the most intriguing natural spectacles making them highly attractive spots for tourists nowadays. On the other hand, they claim human lives, destroy infrastructure, and affect the local as well as the global climate. Understanding and mitigating the dangers of volcanic activity is therefore a major societal task. In this proposal, we address one key aspect of volcanic activity, the transport of magma in a volcanic conduit prior to an eruption, through a detailed modeling study. We specifically focus on strombolian eruptions as they are quite frequent, easy to observe from a safe distance, and a huge amount of different data is available for such eruptions to verify various aspects of numerical models. Models for strombolian explosions, including the ejection of pyroclasts and volcanic gases, call for the rise of large gas slugs (conduit filling gas bubbles, significantly longer than wide) in volcanic conduits that carry a certain overpressure. In between those eruptions, the observed passive degassing is currently explained by two-phase convection in the conduit. Regardless of which of these models is considered, the complex rheology of the magma as a mixture of melt/crystals/bubbles is one of the most fundamental controls on its behavior. In our model, rheological properties of the magma will be derived directly from a thermodynamic model during runtime taking into account cooling/degassing/crystallization of the melt in disequilibrium during transport through the conduit. Knowing the exact composition as well as bubble and crystal content, we employ current models for calculating the viscosity of such a three-phase system. This rheological model will then be implemented into a computational fluid dynamics model to study the gas slug and two-phase convection regimes. Model input parameters will be chosen to best match composition/temperature of magma of Stromboli volcano, Italy. Key questions which will be answered by this project include: 1) How does rheology impact the rise of gas slugs? 2) Are there rheological regimes that promote the development of trains of gas slugs that would explain consecutive eruption pulses? 3) How do transport processes in volcanic conduits change if conduits are not modeled as rigid pipes but rather as hot thermal anomalies in a volcanic edifice? 4) What is the effect of reaction kinetics (non-equilibrium thermodynamics) on transport processes in volcanic conduits? Observations of activity at Stromboli volcano, like ejection velocities, number of pulses during a strombolian eruption, degassing rates, and crystal fraction in ejecta, will be used to test the validity of the model results.

人类对火山喷发的兴趣可能与它的存在一样古老，因为一方面，火山为农业提供了极其肥沃的土壤，导致火山上或附近的首选定居地，此外，它们可能是最有趣的自然奇观之一。另一方面，它们夺走了人们的生命，破坏了基础设施，并影响了当地和全球的气候，因此了解和减轻火山活动的危险是一项重大的社会任务。在该提案中，我们通过详细的模型研究解决了火山活动的一个关键方面，即火山喷发前岩浆在火山管道中的输送，我们重点关注斯特龙博式喷发，因为它们非常频繁，易于从安全距离观察到。此类喷发需要大量不同的数据来验证斯特龙博式爆炸的各个方面的模型，包括火山碎屑和火山气体的喷射。具有一定超压的火山管道中的大气体段塞（管道内充满气泡，长度明显大于宽度）的上升，目前观察到的被动脱气现象可以通过管道中的两相对流来解释。考虑到这些模型，岩浆作为熔体/晶体/气泡的混合物的复杂流变性是对其行为的最基本控制之一。岩浆的流变特性将直接从运行时的热力学模型得出，考虑到熔体在通过管道传输过程中不平衡的冷却/脱气/结晶，我们采用当前的模型。然后，该流变模型将被应用到计算流体动力学模型中，以研究气段塞和两相对流模型的输入参数。将选择与意大利斯特龙博利火山的岩浆成分/温度最匹配的项目，该项目将回答的关键问题包括：1）流变学如何影响气段塞的上升？2）是否存在促进发展的流变机制？可以解释连续喷发脉冲的气体段流序列？ 3) 如果火山管道不是建模为刚性管道而是建模为，火山管道中的传输过程会如何变化？火山建筑物中的热热异常？ 4) 反应动力学（非平衡热力学）对火山管道传输过程的影响是什么？对斯特龙博利火山活动的观察，如喷射速度、斯特龙博利火山喷发期间的脉冲数、排气速率和喷射物中的晶体分数将用于测试模型结果的有效性。