FIAMME: (An international collaboration for a) Framework for Ignimbrite Analysis Methodologies for Modelling and hazard Evaluation

火山碎屑密度流(PDC)是火山喷发期间形成的致命的火山灰、气体和岩石流。它们可以在内部温度高达1000摄氏度的情况下以每小时200公里的速度行驶。它们对活跃的火山中心附近不断增加的人口构成了最大的火山危害之一，自公元1600年以来造成了90,000多人死亡。了解这些洋流是如何形成的，以及是什么控制了它们在时间和空间上的动态流动行为，对于改进我们用于危险评估的预测模型是至关重要的。可悲的是，我们对私营部门议会的了解仍然有限，它们的发生继续导致悲剧。即使是相对较小的PDC也可以跨越山丘和障碍，甚至跨越水路，行驶数十公里。它们的破坏力也很大，因为它们能够携带巨大的火山巨石，非常耐磨，可以在大片地区沉积数十米厚的沉积物。它们的行为由它们的内部动力学控制，比如不同的火山灰和岩石颗粒如何相互作用，它们之间的气体压力，以及电流对其流经的地面的响应。至关重要的是，我们不仅要了解它们的内部动力学，而且要能够定义描述它们的基本方程，以便建立更好的危险模拟。但是，我们看不到火山喷发时火山喷发中心内部流动的情况，所以这些内部动力学对美国来说是未知的。当火山喷发中心流动时，它们会沉积火山灰和岩石，留下它们在岩石中经过的记录。这些沉积物的结构可能非常复杂，捕捉到了PDC在一段时间内的行为似乎发生了什么变化。我们对PDC的理解在很大程度上是基于我们对这些矿床的分析(实际上，在这些矿床中，它们不会沉积甚至被侵蚀)，但这些解释中的许多都是投机性的。尽管我们对私营部门委员会的了解取得了重大进展，但我们对其物理过程、这些过程如何随时间和空间变化、以及这如何导致其高度机动性和破坏性行为的理解仍然存在根本差距。数值模型和水槽试验旨在解决这些研究空白。我们可以在不同的尺度上模拟PDC的某些方面，以描述它们的基本物理。然后，我们希望建立计算机模型，模拟PDC，并预测它们在火山喷发期间可能流向哪里。这将改变对生活在火山灾害中的社区的风险评估。到目前为止，作为一个研究社区，我们还无法对我们从实地研究中了解的这些水流的复杂性进行建模。我们没有系统地收集正确的数据，也没有商定的衡量标准来输入我们的模型。测试矿床性质和形成它们的洋流之间关系的模型是至关重要的，但由于缺乏一致收集的、可比较的、可量化的野外矿床数据集来提供信息和进行验证，这些模型受到了阻碍。该项目旨在将实地研究、数值模型和水槽实验方面的全球专家聚集在一起，以应对这一挑战。我们将为所有已知的PDC矿床案例研究建立一个数据库，确定我们描述和分析矿床所需的最可靠的方法，并制定一个框架，以指导下一代火山学家。

Pyroclastic density currents (PDCs) are deadly flows of ash, gas and rocks that form during volcanic eruptions. They can travel up to 200 km/h with internal temperatures up to 1000 degC. They pose one of the greatest volcanic hazards to ever-increasing populations near active volcanic centres, and are responsible for over 90,000 deaths since 1600 AD. Understanding how these currents form and what controls their dynamic flow behaviour in time and space is fundamental to improving the predictive models that we use for hazard assessments. Sadly, our understanding of PDCs is still limited, and their occurrence continues to result in tragedies. Even relatively small PDCs can travel tens of kilometers, over hills and barriers, and even over water. They are also very destructive as they are capable of carrying large volcanic boulders, are highly abrasive, and can deposit tens of meters of sediment across wide areas. Their behaviour is controlled by their internal dynamics, such as how the different particles of ash and rock interact with each other and the gas pressure between them, as well as how the current responds to the ground surface over which it travels. It is critically important that we not only understand their internal dynamics, but are also able to define fundamental equations that describe them, in order to build better hazard simulations. But, we can't see inside a PDC as it flows during an eruption, so these internal dynamics are unknown to us.As PDCs flow, they deposit ash and rocks, leaving behind a record of their passing in the rocks. The structure of these deposits can be highly complicated, capturing what appear to be changes in how the PDC was behaving through time. Our understanding of PDCs has been largely driven by our analysis of these deposits (and indeed, where they do not deposit and even erode), but many of these interpretations are speculative. Despite significant advances in our understanding of PDCs, there are still fundamental gaps in our understanding of their physical processes, how these change with time and space, and how this results in their high mobility and destructive behaviour. Numerical models and flume experiments aim to address these research gaps. We can simulate certain aspects of PDCs, at various scales, to describe their fundamental physics. We hope to then build computer models that simulate PDCs and predict where they may flow during volcanic eruptions. This would transform hazard assessment for communities living with volcanic hazards. To date, as a community of researchers we haven't been able to model the complexity of these currents that we understand from our field studies. We have not systematically collected the right kind of data, and do not have agreed measurement standards to feed into our models. Models that test the relationships between deposit properties and the currents that formed them are critical, but are hindered by a lack of consistently collected, comparable, quantified datasets of field deposits to both inform and validate against. This project aims to bring together global experts in field studies, numerical models and flume experiments to address this challenge. We will develop a database of all known case studies of PDC deposits, identify the most robust methodologies we have to describe and analyse deposits and develop a framework that will guide a future generation of volcanologists.