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，火山为耕种提供了极其肥沃的土壤，从而导致了火山或附近的首选环境地面。此外，它们可能是最吸引人的自然眼镜之一，使其成为如今的游客。另一方面，他们夺取人类的生命，破坏基础设施，并影响当地和全球气候。因此，了解和减轻火山活动的危险是一项主要的社会任务。在此提案中，我们通过详细的建模研究讲述了火山活动的一个关键方面，即火山行为中岩浆在火山行为中的运输。我们特别关注史克洛尔（Strombolian）的爆发，因为它们经常频繁，从安全的距离上易于观察，并且可用于此类喷发可用于验证数值模型的各个方面。在火山导管中，史克洛利亚爆炸的模型，包括弹出火山细胞和火山气体的射出，要求大型气体sl（导管填充气泡，明显长于宽）的升高）载有一定的过度压力。在这些喷发之间，目前观察到的被动式脱气是通过导管中的两相连接来解释的。无论考虑哪种模型，岩浆作为熔体/晶体/气泡的混合物的复杂流变学都是其行为的最基本控制之一。在我们的模型中，岩浆的流变特性将在运行时直接源自热力学模型，考虑到通过管道运输过程中熔体的冷却/脱气/结晶。了解确切的组成以及气泡和晶体含量，我们的当前模型用于计算这种三相系统的粘度。然后，该流变模型将被实施到计算流体动力学模型中，以研究气体slug和两相连接方案。将选择模型输入参数以最佳匹配意大利Stromboli火山的岩浆的组成/温度。该项目将回答的关键问题包括：1）流变学如何影响气体的兴起？ 2）是否存在促进可以解释持续脉动的气体弹药列车发展的流变系统？ 3）如果导管未建模为刚性管道，而是火山建筑物中的热热异常，则火山导管中的运输过程如何变化？ 4）反应动力学（非平衡热力学）对火山导管中的传输过程有什么影响？将使用驱动速度，茎射击期间的射出速度，脉冲速度的数量，脱气速率和射流中的晶体分数的观察结果来测试模型结果的有效性。