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

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.