Fragmentation and flow of gas-particle mixtures in volcanic systems

火山系统中气体颗粒混合物的破碎和流动

• 批准号: NE/W006286/1
• 负责人: Thomas Jones
• 金额: $ 55.84万
• 依托单位: Lancaster University
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2022
• 资助国家: 英国
• 起止时间: 2022 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FW006286%2F1
• 关键词: Fragmentation; flow; gas; particle; mixtures

The transport of gas and particle mixtures are a widespread phenomenon, both in industry and in the natural world. In the geosciences these gas-particle mixtures exist during sediment transport by the wind, meteorite impacts, rock and snow avalanches and explosive volcanic eruptions. In this research proposal we focus on gas-particle flows produced during volcanic eruptions, although we expect the physics uncovered will be portable to these other disciplines and plan to host a multidisciplinary workshop to facilitate knowledge transfer. Ten percent of the world's population (i.e. 100's of millions) live within 100 km of an active volcano. Furthermore, this number is set to rise with the increasing global population. During all explosive volcanic eruptions pyroclastic density currents (PDCs) can form - high temperature multiphase mixtures of rock and gas that rapidly flow away from the volcanic vent. These phenomena are the most lethal of all volcanic hazards and are responsible for more than a third of volcanic related fatalities. However, despite the lethal nature of pyroclastic density currents we currently lack accurate models to forecast the runout distance achieved by these flows and thus any hazard maps and mitigation strategies are inherently limited. To improve our numerical forecasting models, we need to understand the complex internal flow dynamics within these 'opaque' and hazardous flows. Direct internal observation is not possible, but controlled laboratory experiments offer a way to rigorously study these otherwise hidden phenomena. Specific and targeted experiments aimed at providing key input parameters for numerical flow simulations offer a clear way forward.During this research programme, we will use two types of scaled laboratory experiments to investigate these phenomena in a controlled and observable manner. Firstly, experiments using a rheometer will measure the flow behaviour (e.g. viscosity; mobility) of natural volcanic gas-particle mixtures. We will quantify how the particle size distribution and gas flow conditions effect the mobility of these flows. Secondly, natural volcanic particles (e.g. bubbly volcanic glass, crystals, rock fragments) will be suspended in air to form a gas-particle mixture at a range of conditions relevant to the volcanic system. The experimental products will be characterised for their size, shape, and abundance as a function of time (i.e., transport distance). This will allow us to quantify the rate at which volcanic particles break, round and change their relative abundance during flow. This will lead to a comprehensive understanding of how the particle textural properties (e.g. size, shape) change during flow and how, in turn, these changes alter the mobility of pyroclastic density currents. These experimental data, on flow conditions and particle breakage, derived from new state-of-the-art techniques will be incorporated into existing 3D numerical flow models. Numerical simulations will be performed on a case volcano (Tungurahua, Ecuador). This will allow us to illustrate, and quantitatively assess, the impact this 'new physics' has on existing pyroclastic density current models and importantly, their predicted run out distances. In collaboration with the Geophysical Institute of Ecuador these novel results will be used to critically evaluate current hazard maps and risk mitigation strategies. This research programme will therefore provide a platform upon which reliable PDC models and forecasts can be built for eruptions worldwide. Ultimately this will minimise the human and economic cost of these hazardous geophysical flows.

在工业和自然世界中，气体和颗粒混合物的运输都是一种广泛的现象。在地球科学中，这些气体粒子混合物在风，陨石冲击，岩石和雪地雪崩和爆炸性火山喷发过程中存在。在这项研究建议中，我们专注于火山喷发期间产生的气粒流，尽管我们希望发现的物理学将适合这些其他学科，并计划举办一个多学科的研讨会，以促进知识转移。世界人口中有百分之十（即100万百万）居住在一座活火山的100公里以内。此外，随着全球人口的增加，这个数字将增加。在所有爆炸性火山喷发中，火山碎屑密度电流（PDC）都可以形成 - 岩石和气体的高温多相混合物，从火山通风口迅速流出。这些现象是所有火山危害中最致命的现象，并造成了三分之一以上的火山相关死亡。但是，尽管火山碎屑密度电流的致命性质，但我们目前缺乏准确的模型来预测这些流量所达到的跳动距离，因此任何危险图和缓解策略固有地受到限制。为了改善我们的数值预测模型，我们需要了解这些“不透明”和危险流中的复杂内部流动动力学。无法直接观察，但是受控实验室实验提供了一种严格研究这些原本隐藏现象的方法。旨在为数值流量模拟提供关键输入参数的特定实验实验提供了一种明确的方向。在此研究计划中，我们将使用两种类型的规模实验室实验来以可控且可观察的方式研究这些现象。首先，使用流变仪的实验将测量天然火山气体混合物的流动行为（例如粘度；迁移率）。我们将量化粒度分布和气流条件如何影响这些流的迁移率。其次，天然火山颗粒（例如起泡的火山玻璃，晶体，岩石碎片）将被悬浮在空气中，以在与火山系统相关的一系列条件下形成燃气粒子混合物。实验产品的大小，形状和丰度是时间的函数（即传输距离）的特征。这将使我们能够量化火山颗粒在流动过程中破裂，圆形并改变其相对丰度的速率。这将导致对流动过程中粒子纹理特性（例如尺寸，形状）如何变化以及这些变化如何改变火山碎屑密度电流的迁移率的全面理解。这些实验数据（关于流量条件和粒子破裂，源自新的最先进技术的粒子破裂，将纳入现有的3D数值流量模型中。数值模拟将在案例火山（厄瓜多尔Tungurahua）上进行。这将使我们能够说明和定量评估这种“新物理学”对现有的火山碎屑密度电流模型的影响，并且重要的是，它们的预测距离距离。与厄瓜多尔地球物理研究所合作，这些新型结果将用于批判性地评估当前的危害图和风险缓解策略。因此，该研究计划将提供一个平台，可靠的PDC模型和预测可以在全球爆发中构建。最终，这将最大程度地减少这些危险地球物理流的人类和经济成本。