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.

气体和颗粒混合物的输送是一种普遍现象，在工业和自然界中都是如此。在地球科学中，这些气粒混合物存在于风、陨石撞击、岩雪雪崩和火山爆发的沉积物输送过程中。在这项研究提案中，我们重点关注火山喷发期间产生的气粒流动，尽管我们预计所发现的物理学将可移植到这些其他学科，并计划主办一次多学科研讨会，以促进知识转移。世界上百分之十的人口(即亿万S)生活在活火山周围100公里以内。此外，随着全球人口的增加，这一数字将会上升。在所有火山爆发期间，火山碎屑密度流(PDC)可以形成岩石和气体的高温多相混合物，并迅速从火山口流出。这些现象是所有火山灾害中最致命的，导致了三分之一以上的与火山有关的死亡。然而，尽管火山碎屑密度流具有致命性，但我们目前缺乏准确的模型来预测这些流所达到的超限距离，因此任何危险地图和缓解策略都固有地受到限制。为了改进我们的数值预报模型，我们需要了解这些“不透明”和危险流动中复杂的内部流动动态。直接的内部观察是不可能的，但受控的实验室实验提供了一种严格研究这些原本隐藏的现象的方法。旨在为数值模拟提供关键输入参数的具体和有针对性的实验提供了一条明确的前进道路。在本研究计划中，我们将使用两种规模的实验室实验来以受控和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气火山气体-颗粒混合物的流动特性(例如，粘度；流动性)。我们将量化颗粒大小分布和气流条件如何影响这些流动的流动性。其次，在一系列与火山系统有关的条件下，天然火山颗粒(如起泡的火山玻璃、晶体、岩石碎片)将悬浮在空气中，形成气体-颗粒混合物。实验产品将根据它们的大小、形状和丰度作为时间的函数(即运输距离)进行表征。这将使我们能够量化火山颗粒在流动过程中破裂、变圆和改变其相对丰度的速度。这将导致全面了解颗粒结构属性(如大小、形状)在流动过程中如何变化，以及这些变化反过来如何改变火山碎屑密度流的流动性。这些来自最新技术的关于流动条件和颗粒破碎的实验数据将被纳入现有的3D数值流动模型中。将对一座案例火山(厄瓜多尔通古拉瓦)进行数值模拟。这将使我们能够说明并定量评估这一‘新物理’对现有的火山碎屑密度流模型的影响，更重要的是，它们预测的耗尽距离。这些新的成果将与厄瓜多尔地球物理研究所合作，用来批判性地评估目前的危险地图和减少风险战略。因此，这一研究方案将提供一个平台，在此平台上可以建立可靠的火山喷发预测模型和预测世界各地的火山喷发。最终，这将使这些危险的地球物理流动的人力和经济成本降至最低。