Can you stop a PDC? Assessing the impact of natural and engineered barriers on deadly volcanic flows in the built environment


Pyroclastic density currents (PDCs) are a major hazard at explosive and dome-forming volcanoes, impacting communities around the world. These hot flows of ash, gas and rock are known to have high mobility, travelling at great speed in excess of 450 mph and overtopping topographic barriers, sometimes kilometres in height at great distances from source. Experiments and field analyses have suggested a variety of ways in which density-stratified pyroclastic density currents can interact with topography. They can overtop topographic barriers or partially overtop them by detaching a more dilute cloud from the dense undercurrent. The initial momentum of the current may carry the leading edge over topographic barriers on initial encroachment, or the mass flux may have to increase above a certain threshold before the current is able to overtop the obstacle. Alternatively, the topography may have to be modified by deposits accumulating against the topographic barrier before a sustained density current can surmount the barrier. Conversely, PDCs have been recorded to have been reflected or deflected by even small topographic barriers. However, these interactions have not been quantified, particularly for fluidised, granular currents, and remain poorly understood. Natural barriers and topographic obstacles have produced unpredicted and ultimately fatal misinterpretations of current direction in the past.

There is a growing need to mitigate against PDC hazard, and engineered topographic barriers are a potential solution that needs to be explored. Furthermore, investigation of PDC interactions with infrastructure will contribute to a better understanding of evolution of hazard where PDCs reach and inundate the built environment. For example, as a PDC interacts with obstacles, what changes in dynamic pressure and therefore destructive power, should we expect? How is the potential for diversion past, or burial of, infrastructure impacted by changes in current dynamics and ability to deposit?

This project will assess the response of fluidised and unfluidised PDC analogues to different obstacle geometries, assessing the stresses imparted, and the nature of the resulting currents and deposits to different engineering solutions and the built environment. 


  1. Develop an experimental flume set-up to model how PDCs encroach, overtop, or are deflected by a variety of natural and engineered topographic barriers
  2. Quantify changes in depositional behaviour, and the resultant deposit architecture, before and after a variety of natural and engineered topographic barriers
  3. Interrogate how different obstacle geometries influence current dynamics (including velocity, stratification, sediment concentration and dynamic pressure) and therefore may change the nature of the hazard through time and space.
  4. Understand how interaction with these geometries controls sedimentation and thus infrastructure burial


The goal is a quantitative assessment of risk modification through varying barrier design, enhanced understanding of the influence of natural topography, and a better understanding of the interaction of PDCs with the built environment. This opens new possibilities for understanding risk and resilience for communities living near active volcanoes. It will shed light on the fundamental behaviours of these catastrophic volcanic flows, and improve the framework in which we interpret their deposits. 


The project will provide training in: (i) geological fieldwork, (ii) the set-up of experimental flumes, (iii) the fluid dynamics of density currents, and (iv) modelling and analytical skills. You will be associated with the Catastrophic Flows Research Cluster and will work with Dr Rebecca Williams (School of Environmental Sciences, University of Hull), Dr Rob Thomas (Energy & Environment Institute, University of Hull),  Dr Pete Rowley (University of Bristol) and Dr Natasha Dowey (Sheffield Hallam University). The University of Hull has a thriving postgraduate community and the postgraduate training programme provides a full range of courses covering research techniques, scientific methods, information technology, scientific writing and statistical analyses, which are tailored to the needs of each student. Supervision will involve regular meetings between all supervisors. 

Student profile

You should have an interest in volcanology, and geohazards, and be enthusiastic about using a range of different techniques, to better understand density current dynamics. Students from geoscience, engineering, or numerical backgrounds are all encouraged. If you have any informal queries about this project please feel free to contact Rebecca Williams (

Find out more via our free webinar

The University of Hull is running a webinar at 6pm on 21 November to provide more information about this project and the eight other projects hosted by Hull. The webinar will close with a Q&A giving you the opportunity to delve deeper into research opportunities, training provision and potential career paths. Book your place.