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.

人类对火山爆发的兴趣可能和它的存在一样古老，因为一方面，火山为农业提供了极其肥沃的土壤，导致人们更喜欢在火山或火山附近定居。此外，它们可能是最有趣的自然景观之一，使它们成为当今游客极具吸引力的景点。另一方面，它们夺去人的生命，破坏基础设施，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重大的社会任务。在这个提议中，我们通过详细的建模研究，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运输。我们特别关注斯特龙博利火山喷发，因为它们非常频繁，易于从安全距离观察，并且有大量不同的数据可用于此类喷发，以验证数值模型的各个方面。斯特龙博利爆炸模型，包括火山碎屑和火山气体的喷射，要求在携带一定超压的火山管道中上升大的气栓（充满气泡的管道，明显长于宽）。在这些喷发之间，所观察到的被动脱气目前被解释为管道中的两相对流。无论考虑这些模型中的哪一个，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。在我们的模型中，岩浆的流变特性将直接从运行时的热力学模型，考虑到冷却/脱气/结晶的熔体在不平衡的运输过程中通过导管。知道确切的组成以及气泡和晶体含量，我们采用当前的模型来计算这种三相系统的粘度。然后将该流变模型应用到计算流体动力学模型中，以研究气弹和两相对流状态。将选择模型输入参数以最佳匹配意大利Stromboli火山岩浆的成分/温度。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)是否有流变机制促进了气栓序列的发展，从而解释了连续的喷发脉冲？3)如何运输过程中的火山管道的变化，如果管道不是模拟为刚性管，而是作为热异常的火山建筑物？4)反应动力学（非平衡热力学）对火山管道中的运输过程有什么影响？在斯特龙博利火山的活动，如喷射速度，脉冲数在斯特龙博利喷发，脱气率，和喷出物中的晶体分数的观测，将被用来测试模型结果的有效性。