Pyroclastic density currents (PDCs) are dangerous multiphase flows originating from volcanic eruptions. PDCs cause more than a third of volcanic fatalities globally and, therefore, development of robust PDC hazard models is a priority in volcanology and natural hazard science. However, the complexity of gas–particle interactions inside PDCs, as well as their hostile nature, makes quantitative measurements of internal flow properties, and the validation of hazard models, challenging. Within the last decade, major advances from large-scale experiments, field observations and computational and theoretical models have provided new insights into the enigmatic internal structure of PDCs and identified key processes behind their fluid-like motion. Recent developments have also revealed important links between newly recognized processes of mesoscale turbulence and PDC behaviour. In this Review, we consider how recent advances in PDC research close the gaps towards more robust hazard modelling, outline the need to measure the internal properties of natural flows using geophysical methods and identify critical future research challenges. Greater understanding of PDCs will also provide insights into the dynamics of other natural gravity currents and high-energy turbulent multiphase flows, such as debris avalanches and turbidity currents.

火山碎屑流（PDC）是危险的多相流，起源于火山喷发。PDC在全球造成超过三分之一的火山死亡，因此，开发可靠的PDC灾害模型是火山学和自然灾害科学的重点。但是，PDC内部气体-颗粒相互作用的复杂性以及其敌对性使得内部流动特性的定量测量以及危害模型的验证变得充满挑战。在过去的十年中，大规模实验，现场观察以及计算和理论模型的重大进步为PDC的神秘内部结构提供了新见解，并确定了其流体状运动背后的关键过程。最近的事态发展还揭示了新认识的中尺度湍流过程与PDC行为之间的重要联系。在这篇综述中，我们考虑了PDC研究的最新进展如何弥合向更可靠的危害建模的差距，概述了使用地球物理方法测量自然流的内部特性并确定未来关键研究挑战的需求。对PDC的更多了解还将提供对其他自然重力流和高能湍流多相流（例如碎屑雪崩和浊流）动力学的见解。概述了使用地球物理方法测量自然流的内部特性并确定未来关键研究挑战的需求。对PDC的更多了解还将提供对其他自然重力流和高能湍流多相流（例如碎屑雪崩和浊流）动力学的见解。概述了使用地球物理方法测量自然流的内部特性并确定未来关键研究挑战的需求。对PDC的更多了解还将提供对其他自然重力流和高能湍流多相流（例如碎屑雪崩和浊流）动力学的见解。